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X-band radar wave Observation system

1. WINS Proxy Enabled E DNS Suffix Search List campus vims edu vims edu Ethernet adapter Local Area Connection Connection specific DNS Suffix vims edu aie vay dae fa Sareea va tie gt fae se 70 10 103 Subnet Mask gt o e s e e mo f 255 255 6 Default Gateway 70 10 206 DHE Servers seses fate ae E 70 2 126 70 2 1299 Primary WINS Server I 70 2 50 Secondary WINS Server E 70 30 64 C Documents and Settings hokyung gt Fig 7 2 An example of the window of command prompt showing the MAC address which is the same as the 12 digit physical address An individual NIC has its own MAC different with other NICs A potential problem of using LAN is that the firewall for security reasons may prevent computers to communicate across the firewall If the host to be connected is outside of the firewall of a LAN a user may have problem When this happens the LAN system administrator must be consulted for solving this problem 94 7 3 Remote Access by Modem Considering the limited network resource at radar sites WOM by an analog telephone line or a wireless telephone connection might be a choice for remote operation In this report the wireless part has not been tested yet but most of the technique details on WOM have been addressed by a regular modem A dedicated phone number and a modem are required at both the remote host PC and the user computer in orde
2. ky plane and form infinite number of circles with different radius but the same center at kx ky 0 An example of selected number of those collapsed shells are given in Fig 6 12 If one plots the dispersion shell in 3 D format then the amount of energy would be in the 4 dimension This makes the plot of 3 D energy display impossible If cutting the dispersion shell for each frequency band then a finite number of 2 D plots Fig 6 13 can be resulted to represent the energy for each particular frequency band Or the energy for all frequency bands can be plotted together as that displayed in Fig 6 12 rA 7 N ol Z i one N f ye A a AN Pii k 1 m 9 o ot Te J aN aN 0 3 0 2 0 1 0 0 1 0 2 0 3 Fig 6 12 Example to show a collapsed dispersion shell in 2 D plot Each dashed circle represents the dispersion relationship between wave frequency and wave number The energy distribution given here is for 10 00 Feb 19 2004 88 Using the definition given by Young et al 1985 the SNR can be calculated relatively easy This is because the energy at the spectral peak can be found by one single Matlab command emax max max max e where e is a 3 D wave spectrum energy distribution matrix However there is no specific rule on where is the so called well away from the dispersion shell In this study the average energy on a circular belt similar to the circle displayed in Fig 6 13b with a belt width of abo
3. Coastal Engineering 37 3 4 513 527 Borge N J C K Reichert J Dittmer and W Rosenthal 1998 WaMoS II a wave and current monitoring system Presented at the COST 714 conference Paris Borge N J C K Reichert and J Dittmer 1999 Use of nautical radar as a wave monitoring instrument Coastal Engineering 37 331 342 Borge N J C and C G Soares 2000 Analysis of directional wave fields using X band navigation radar Coastal Engineering 40 375 391 Dean R G and R A Dalrymple 1992 Water Wave Mechanics for Engineers and Scientists World Scientific Singapore 353pp Doong D J L C Wu L Z H Chuang and C C Kao 2001 Directional Wave Spectra Derived by DWT of Marine Radar Images Proceedings of the International Conference on Port and Maritime R amp D and Technology ICPMRDT 2001 Oct 29 31 Singapore 609 615 Doong D J L C Wu C C Kao L Z H Chuang 2003 Wavelet Spectrum Extracted from Coastal Marine Radar Images Proceedings of the 13th International Offshore and Polar Engineering Conference ISOPE 2003 Honolulu Hawaii USA May 25 30 258 264 Gangeskar R 2002 Ocean current estimated from x band radar sea surface images IEEE Transactions on Geoscience and Remote Sensing 40 4 783 792 Gurgel K W G Antonischki H H Essen and T Schlick 1999 Wellen Radar WERA A new ground wave HF radar for ocean remote sensing Coastal Engineering 37 219 234 Hashimoto N T Nagai a
4. D 9t J006 p D 0 04 Cc 2 D g 120 0 02 180 i ig Fs ST 9b Line spectrum with H 1 35 N f If Q w L 0 1 0 0 1 0 2 0 3 0 4 0 5 Frequency Hz Fig 6 7 Wave condition on 16 00 March 23 2005 a Directional spectrum b line spectrum 82 a m s deg T 0 018 x a S 0 014 g 270 90 Joo E wW a b a c i 0 006 z TO 0 002 180 Line spectrum with Hs 1 43 Energy NPIHz 0 0 1 0 2 0 3 04 0 5 Frequency Hz Fig 6 8 Wave condition on 10 00 March 28 2005 a Directional spectrum b line spectrum The last directional wave spectrum diagram 16 00 April 2 2005 Fig 6 9 may represent a nearly developed sea condition The wave energy was relatively concentrated at the frequency between 0 09 0 14 Hz with a small tail on 0 2 Hz 83 m s deg N 0 04 o ae oe feb Z 0 03 B 270 i Wd 9 5 0 02 5 2 S 240 es a 120 jg 5 _ a 180 T T T T Line spectrum with Hs 1 44 0 0 1 0 2 0 3 04 05 Frequency Hz Fig 6 9 Wave condition on 16 00 April 2 2005 a Directional spectrum b line spectrum 6 4 Wave Data from CHLV2 and VAO001 Besides the wave measurement conducted for this project other wave data are also used There are two wave stations at the vicinity of Virginia Beach The 1 one is a NOAA station CHLV2 see Fig 6 1 The o
5. cessssssssssererrrreesssrrrrrreereen 21 3 3 Signal Wires for Trigger and Radar Images ceeeee ence ence es 22 3 4 C program for Radar Image Data Acquisition eeceeeee eee e ees 25 Chapter 4 Software for Data Analysis ssssssssecsssesssessrerrresererrseerrrrrerees 31 4 1 Principle of Data Analysis sus io cerseevesiseeas texaeesbostsaeueysisbeai senses 31 4 1 1 1 D wave spectrum analysis ccccccceeessecccerrereerrrrrrerreren 31 4 1 2 2 D wave spectrum analysis cece cece eee eee e eee eeneeeeaeaes 33 4 1 3 3 D WAVE spectrum analysis 225550 casven ning sie eeaenti es eeeyeneeny see 36 4 2 Given Regular Wave Fields is soce tie ceiceasdse ses sien dda daeeaaeees See sis 40 4 3 A Given Random Wave Field csc0scc secessdenceeaeeasaieeseradespawens 48 Chapter 5 Data Process for Radar Images scceceeee eee e eee eee ne ene eeaeeneees 52 5 1 Minimize Signal Distortion ssssssssesessesssssrerrrrrrrrrrrrsesrrrreeeere 52 5 2 Average Radar Signal Strength Sa cc ccvscscscseags codigos cad vaeseeetvcaeenaes 57 5 3 Interpreting Radar Image for a Small Rectangular Domain 57 5 4 FFT Analysis on Radar Images ecceeeee eee eeneeeeeeeeaeeeaeees 60 5 5 The Average Radar lmawe lt 125274 sce sc ave opacities ede nen nnde hedaowantonee 71 Chapter 6 Calibration of X band Radar Wave Measurements 0 000 74 Gils Siar NVaVe CAUSE Gs eve
6. digitize every burst line images and 2 digitize one line in every 4 lines The results show little difference and thus the second option was used for the rest of data acquisition Resolution in Radial Direction The burst duration also called pulse width 80 ns in this case also controls the image quality in the radial direction For example there are about 800 80 x 10 s 10 x 10 hz waves emitted from the antenna during this 80 ns duration When the first wave of this wave train hit a target and reflected the rest waves are still coming and the reflection will be continued until the end of the 80 ns Thus a radar see the target for the entire 80 ns and changes the subject length from 1 meter long in the radial direction to an image length of 24 m 800 0 03 m where 0 03 m is the wave length of 10 Ghz EM wave For this reason the minimum length observed from radar observation would be 24 m While scanning at 100 Ms s for 32 us to cover a range of 5 km the number of data collected represents a distance of 5000 m Thus a resolution of 5000m 3200 point 1 57 m can be found This resolution is significantly higher than the radar image resolution 24 m and thus not necessary required If scanning with a rate of 25 MS s 17 the radial resolution would be about 6 25 m which is still much finer than that of the image resolution For this reason a scanning rate of 25 to 30 MS s would be sufficient Datafile Size F
7. 00 March 23 D and Dg information indicate that waves were mainly coming from ENE direction and varied frequently between 70 and 90 Figs 6 4c 6 4d and 6 5 78 Peak Period sec Significant wave height m Dominant dir deg Peak Period Dir deg 03 24 03 29 04 03 04 08 Time day 0 i 03 14 03 19 Fig 6 4 Time series records from the wave gauge a significant wave height Hs the arrows indicate when a detailed spectrum analysis was given in Fig 5 6 b peak wave period c Dominant wave direction d direction of the peak period 79 pat Direction bearing Count Fig 6 5 Wave roses for the period from 11 00 March 16 22 00 April 6 2005 a Direction of wave period at the peak energy and b dominant wave direction Table 6 1 Maximum significant wave height and wave peak period estimated from the wave gauge tripod Date Time H m Tp sec 03 18 05 01 00 1 32 8 33 03 23 05 16 00 1 35 9 09 03 28 05 10 00 1 43 7 14 04 02 05 16 00 1 44 8 33 Directional wave spectra were provided at four selected times H gt 1 m see Table 6 1 and Figs 6 6 to 6 9 Upper panel in Figs 6 6 to 6 9 represent the directional distribution of wave energy The lower panels in these figures show the distribution of spectral densities for each frequency Notice that the direction in these figures means the wave propagation direction DIWASP ver 1 1 which is exactly 180 degree
8. 1 66667 s Each image has 128 x 128 points in the x and y direction respectively with a grid resolution of 8 m in both the x and y directions At a frequency that is close to the wave peak energy frequency the program calculated directional spreading is probably more than 10 degrees Fig 4 13 This may be because of the selected noise level of 25 Nevertheless the direction is correctly calculated as 90 degrees in the kx ky plane After transferred it to the f O plane it can 48 be seen more clearly that the peak energy frequency is around 0 1 Hz with a main direction of 90 degrees Fig 4 14a This time the energy was spread over a much large domain caused by the nature of random sea The given directional wave spectrum that was used to generate the wave images was also displayed Fig 4 14b A much smooth contour plot for the given directional spectrum is evident The line spectrum Fig 4 15 also shows the results correctly and the significant wave height calculated from the program H 2 81 m has a negligible error of 0 7 Hw 1000 a00 B00 400 DISTANCE Y m 200 200 400 600 800 1000 DISTANCE X m Fig 4 12 First image of a series of random wave fields generated by using DIWASP package with peak wave frequency fp 0 1 Hz H 2 83 m travel toward the positive y axis direction 49 Freq 0 10312 Hz k 1 m 0 2 0 1 0 0 1 0 2 k 1 m Fig 4 13 Results from 3 D FFT in kx k
9. 11 First three rectangular radar images on 10 00 Feb 19 2004 for wave analysis With x y 5 m t 1 66667s domain size 640 x 640 m 65 Freq hz Direction deg b 021904 h10 60 4 40 E m hz 20F L L L 4 4 4 4 0 1 0 2 0 3 04 FREQ hz Fig 5 12 Results from radar images analysis on 10 00 Feb 19 2004 with x y 5 m t 1 66667s domain size 640 x640 m a Directional spectrum b line spectrum swells and some wind waves frequency 0 19 Hz that all coming from E if an 8 off from E is neglected For the calm sea radar images obtained on 21 00 March 2 2004 H 0 5 m at Station CHLV2 see Chapter 6 the first three interpreted rectangular images Fig 5 13 cannot show a clear wave field and the analysis results Fig 5 14 using the middle resolution grid i e 5 x 5 m also cannot show a clear dominant wave The energy is practically spreading in all frequencies and all directions Although the line spectrum still shows a peak wave period of 4 8 s this information may be meaning because of the wide spreading of energy in all directions 66 1240 Signal 1 level 5 4 600 1240 3 2 oe 2 p 0 600 1240 1 2 3 3 600 320 0 320 X m Fig 5 13 First three rectangular radar images on 21 00 Mar 2 2004 for wave analysis With x y 5 m t 1 66667s domain size 640 x 640 m 67 Freq hz 150 100 50 0 50 100 150 Direction de
10. EM waves mean longer burst duration Because there are many EM waves in a burst line the radar measured subject length is not the true subject length neither For example for an 80 ns burst duration 8300 EM waves 80 x 10 s 10 x 10 Hz were sent out Because all the waves will cause 11 reflection on a subject an one meter long subject along the track of radar wave beam will be seen as a 24 m long subject 0 03 m 800 waves with the highest signal strength at the center For this reason the burst duration should be kept as short as possible In other words the operation range should be set at the shortest detect range for radar operation when it is used for wave measurements This is a rather important information that needs to be documented in this report The characteristics of radar images discussed in the above paragraphs assume that the resolution for data digitization is infinitely high and the reflection of radar waves is perfect In reality however these will not be the cases and thus the radar images collected are somewhat smeared 2 3 Personal Computer When a X band radar was first used for wave measurements the data analysis and radar control were performed by using a Unix mini computer With the advance of Personal Computer PC the control of radar data acquired and data analysis were transferred to PC a few years ago This study demonstrated that a PC with a Pentium 4 processor of 2 8 Ghz and Windows
11. In attached CD only There are two C programs killtime c and radar c and one control input file radar_single con in this appendix Appendix III Matlab codes for analyzing the radar images for waves In attached CD only There are two Matlab main programs and six functions in this appendix The first main program is imgplt m which is only used to read and plot the raw radar images This program calls two functions read_radar_header m and read_radar_image_chk m to carry out the job The other main program is fft3d_radar m which is the wave analysis program It calls the following functions read_radar_header m read_radar_image m kd fft3dSNR m Jacobian m and circle m to accomplish the job iii Table of Figures Fig 2 1 Setup of a X band radar at a building roof 0 e eee e eee e ee 7 Fig 2 2 The better working area Lp of a radar wave observation system 8 Fig 2 3 Relationship between radar antenna height and the better working area Ly is for an impinge angle of 1 and L is for a possible extension of the better working area by increasing the impinge angle to 0 5 2 0 cceeeeeeeeeeee sence ee ee seen eneenenenes 9 Fig 2 4 For a FURUNO FR8251 radar the radar scanning domain can be specified a Within this domain pulses are generated from the radar control unit at a rate of 2100 pulses s to trigger the burst of radar wave
12. Inlet 49 50 4 49 00 f 50 00 50 00 7 50 7 00 76 W 59 50 59 00 58 50 58 00 57 50 57 00 Fig 6 1 Location map for the X band radar the star wave gauge tripod and the NOAA Station CHLV2 Distance between the radar and the tripod is approximately 570 m A micro controller Onset Computer model TFX 11 in the data logger house controlled the power supply to the transducers and a datalogger carried out the Analog to Digital Conversions ADC of all pressure signals and other auxiliary signals and sent the digitized data to the datalogger manufactured by Persistor model CommLogger BBR for storage All the above functions were executed by running a BASIC programming in the micro controller The analogy pressure signals were digitized at a rate of 2 Hz for 2048 points This means a measurement duration about 17 minutes every hour 75 360 W P3 o 269 b 2 34 1 35 P1 120 Fig 6 2 The star wave gauge a On the moment of deployment b coordinates for wave spectral analysis P1 P2 and P3 represent the location of pressure sensors The center of tripod was selected as the origin Each sensor was located 0 66 m above the seabed Hourly water wave conditions were collected from March 16 to April 12 2005 Unfortunately only data for the first 20 days were good and thus analyzed Data for the last seven days were corrupted for an unclear reason probably caused by a
13. PCI bus caused by the PCI graphic interface card and the Gage ADC card For this reason data measured from the star wave gauge are not used More of this phenomenon will be presented in the discussion section Nevertheless the completed process of using a marine X band radar for wave measurements is completed 90 0 400 800 1200 SN Ry Fig 6 14 Example to show that there is no correlation between the significant wave height and the SNR defined by Young et al 1985 Data for Feb Mar m 142 H 0 551 SNR 0 252 Apr 0 Nov v 2004 SNR Fig 6 15 The relationship between significant wave height H and the second definition of SNR Wave height data are from Sta CHLV2 91 Chapter 7 Remote operation of the radar system It would be better and convenient to have remote access and control of the radar wave observation system presented in previous chapters This is because the radar site is usually far away from the data center and access to the observation results in a timely manner is important Possible options are 1 by Local Area Network LAN and 2 by modem Details on how they can be done are presented in this chapter 7 1 General Requirements For a personal computer PC to have remote access capability a PC with either a WakeOnLan WOL or a WakeOnModem WOM are necessary This means an ATX power supply with standby power for the motherboard is necessary In ge
14. dig out a trench that is parallel to the jetty Because of the relatively deeper water in the trench waves will not be broken there and thus can be clearly seen by the average radar image Fig 5 17a When the sea severity is low Fig 5 17b the alongshore current is also weak and thus the trench is not clear For another relatively severe sea on 21 00 March 19 2004 the trench is again clearly seen Fig 5 18 This time there is another large size signal x from 1000 to 1000 and y from1000 m to 1200 m However more studies are necessary to understand the message of this large size signal 71 rd021704 h18 2000 m 1000 RDO20204 H21 2000 y m 1000 2000 1000 0 1000 2000 Fig 5 17 Averaged radar images at the Virginia Beach a For a relatively severe sea on 18 00 Feb 17 2004 to show two wave breaking lines on the left hand side and b a relatively calm sea on 21 00 March 2 2004 Two offshore buoy sets from the Rudee Inlet are much clear for the calm sea 72 RDO3 1904421 2000 1000 a 1000 2000 x m Fig 5 18 Average radar images at the Virginia Beach on 21 00 March 19 2004 to show the signals that are not understood at this time Two wave breaking lines on the left hand side and a trench are also clearly seen 73 Chapter 6 Calibration of X band Radar Wave Measurements A star wave gauge for directional wave spectrum measurements was launched to measure the water wav
15. frequency domain should be started from minus infinite 2 and ended at positive infinite 00 for an infinite time series For a finite length of time series the frequency domain should be from 0 5 n At to 0 5 n At with zero frequency in the center A function FFTSHIFT for this purpose is also implemented in Matlab For this 1 D case it simply swaps the left and right halves of the computing results indicated by the dashed array between Fig 4 1b and 4 1c FFTSHIFT is useful for visualizing the Fourier Transform with the DC component frequency 0 in the middle of the spectrum The traditional way to present the spectrum is just taking the positive half of the plot either the left half in Fig 4 1b or the right half of Fig 4 1c and double the energy values because of the omission of energy in the negative half frequency domain 32 0 500 1000 1500 2000 Time t s Energy m hz 0 2 0 1 0 0 1 0 2 f hz Fig 4 1 Example of a selected time series and the results of calling FFT a n t with 12 componential waves b energy spectrum by a direct dot product of F f and the conjugate of F f and c energy spectrum after taking FFTSHIFT 4 1 2 2 D wave spectrum analysis A time series record of water surface elevations at specified observation sites along an 1 D spatial domain here denote x n t x can be transferred into frequency and wave number domains by using the 2 D Fourier Transform defined as
16. given in the previous figure Direction ambiguity is associated with this 2 D FFT Energy peaks inside the small circles are the false signals 4 1 3 3 D wave spectrum analysis Similar to 2 D wave spectrum analysis a time series record of water surface elevations at specified observation sites on a horizontal 2 D domain here denotes as x y n4t x y can be transferred into frequency and two wave number kx and ky domains by using the 3 D Fourier Transform defined as follows F f k k nex y e Me e dt dx dy 4 4 36 A function for n dimensional FFT with a finite length of data record FFTN M is also available in Matlab An example of using this function with an artificial signal is given next Now the wave data are n snap shots of the wave field n x y t which was generated according to Eq 4 5 This equation has only one extra term i e 6 t added to produce n snap shots Fig 4 4 with a total of 64 snap shots with At 2 s All other parameters are the same as those given in the previous section except that Ax Ay 7 7985 m and the five wave directions are 160 20 60 65 and 20 degrees respectively n x y t aj cos k cos 8 x k sin O y oj t oj 4 5 The result of calling FFTN F f kx ky is also a 3 D complex matrix with exactly the same dimension as that for the input n x y t 64 frequency band 128 k band and 64 k band There are two ways to present the results in gra
17. it was finally clear that something else was wrong and then lead to the identification of interference on PCI bus Nevertheless this experience prompts the following suggestions In a PC s BIOS setup there are options to turn off devices It is recommended that all the unnecessary devices e g video audio USB parallel serial ports and keyboard should be off and unnecessary hardware should be removed 1100 1000 900 800 700 300 200 100 0 100 200 300 Distance X m Distance Y rn Fig 8 2 The incorrect setting on radar measurement range changes the image size from that in the thin white dotted box to that in a much thicker black dashed box The occasional missing of line images the blue lines produces a strong signal after FFT and the result is that waves are always traveling in a direction parallel to the x axis 100 Select the Minimum Radar Operation Range As mentioned in Chapter 2 6 the burst duration should be short to reduce echo image distortion in the radial direction When operating radar manually however it is quite often to select a large operation domain to see a more complete picture One has to remember to set this option back to minimum domain e g 500 m If not then the radar image will be smeared as shown in Fig 8 2 In the center of this figure if using the short range then the wave face image shall be thin as that marked by the white dashed box Because of using a large operation rang
18. m s the total time for getting the echo waves at 5 km away would be 32 us 2 x 5000 m 3x10 m s During this 32 us for an antenna rotating speed of 36 rpm i e 0 6 rps the antenna will rotate about 0 6 21 32x10 s 0 0001206 rad 0 0069 degrees which is rather a small angle The swept footprint is about 0 6 m 0 000120685 x 5000 m that is much smaller than the lateral EM wave spreading 0 9 in the horizontal and 25 in the vertical direction for a Furuno s 8 ft long open array antenna and thus can be considered as stationary The 0 9 degree horizontal spreading of the EM waves means a 78 m 0 017453 0 9 5000 m footprint at 5 km away This is to say that at a distance of 5 km away a subject with only 1 meter wide will be seen by the radar as a subject with a width of around 70 m although the target will still give the strongest image when it is directly on the center of aradar beam This is because the spread radar beam will see the same target but with a weaker echo signal So instead of seeing a dot subject the radar see an arc subject with fading image on both ends that is much wider in the angular direction than it would be For a Furuno 8251 marine x band radar it sends out 2100 pulses per second to trigger the burst of radio wave beams for detecting subjects For an antenna rotating speed of 36 rpm it means a total of 3500 bursts will be triggered for one radar image The generation of these pulses howeve
19. malfunctioned battery 76 6 2 Data Analysis For the wave spectrum analysis a MATLAB program package for DIrectional WaAve SPectra DIWASP developed by the Center for Water Research University of Western Australia Johnson 2005 was employed In this software package five different estimation methods can be selected depending on the quality or speed of estimations required for details see DIWASP ver 1 1 At this study the Extended Maximum Entropy Method EMEP Hashimoto et al 1993 was selected because it is a good all round method that accounts for errors in the data with a tolerable computation time compared with other methods In the post processing the center of tripod was arbitrary assigned as the origin with the x axis represents the cross shore direction and positive toward the offshore direction The y axis represents the along shore and positive to north Fig 6 2 Wave spectral densities in unit of m Hz for the frequency band 0 01 0 5 Hz with a band resolution of 0 01 Hz were estimated Directional resolution of 2 was selected as an optimized value considering the tradeoff between the resolution and calculation time Through the wave spectral analysis with the layout described above the significant wave height peak period direction of peak period and dominant wave direction can be derived 6 3 Measurement Results Figure 6 3 displays the change of mean water elevation time averaged of each bur
20. possible range of wave period from 5 to 14 seconds the range of deepwater wavelength would be from 37 5 and 306 m In coastal areas say with a water depth of 8 m the wavelength would be from 35 m to 102 m For this reason a grid resolution of 3 5 or 8 m are all fine because at least there are 4 points to represent a wave The possible sizes of the three sub domains are all having at least 3 7 waves in the sub domain and thus also reasonable 59 Image of a rectangular sub domain would be obtained from interpreting the raw radar image Locations of these unevenly spaced raw data are displayed on the left half of Fig 5 6 and the grid locations of an evenly spaced rectangular sub domain are on the right half of Fig 5 6 An example of the first three interpreted rectangular wave images are given in Fig 5 7 for the smallest sub domain The coordinates of these three sub domains are also marked Grid Locations Data Locations 1000 300 800 Y m 700 600 200 100 100 200 X m Fig 5 6 Location map to show the measured image location and the interpreted location for wave analysis 5 4 FFT Analysis on Radar Images Using the techniques given in the previous chapter the analyzed directional wave spectrum is given in Fig 5 8a This dominant wave propagation direction 80 degrees 4 quadrant can be translated as waves comi
21. radar For a different radar model even from the same manufacturer the switches may be different 19 For example another Furuno radar model 1510 uses a heavy duty switch for turning on and off of the power supply and thus require a heavy duty relay to replace the Telcom relay This replacement will affect the location of the relay and the power required for operating that relay Thus an experienced technician is needed for changing this part Radar Antenna 10GhzAc Transmitted Waves 25 K 10 Ghz AC Radar image processing unit l Trigger source ores Display Fig 3 1 System diagram for the radar wave observation system The dotted boxes mark the hardware added for the system and the dashed lines mark the flow of control signals and radar image of the system All solid boxes are from a radar manufacturer 20 Add on Device in PC for Automatic Radar control 1 rT H E Sani Nais TF2 12v NEC P5852506 i x on Telcom relay optoisolator i Aft prey ff i i aa 774 Nais TF2 12v g NEC PS2506 i x rc Telcom relay optoisolator To switchs on i 1 HP i radar control ra f i 4 H I NA ctor Si oan cr een et panel rd J Power r T ff switch pin 7 Digital high low i 7 signal from TFX 11 v o e2e eee 66 d eee DETO P 26 pin connector inside the radar Toward monitor Umt Top view radar screen Standby switch pin Com
22. shell in 2 D plot Each dashed circle represents the dispersion relationship between wave frequency and wave number The energy distribution given here is for 10 00 Feb 19 2004 88 Fig 6 13 Examples to show a fraction of the dispersion shell with energy within that frequency band for radar wave image measured on 10 00 Feb 19 2004 90 Fig 6 14 Example to show that there is no correlation between the significant wave height and the SNR defined by Young et al 1985 cc ecee cece ence eee e ees 91 Fig 6 15 The relationship between significant wave height H and the second definition of SNR Wave height data are from Sta CHLV2 cece 91 Fig 7 1 The window generated when running the program WaveOnLanGui for Fig 7 2 An example of the window of command prompt showing the MAC address which is the same as the 12 digit physical address An individual NIC has its own MAC different with other NICs 1 0 0 0 ccc cece eee c cece eee ee eens ene ea eee ens 94 Fig 7 3 The device connection diagram for WOM using external or internal Fig 8 1 A raw radar image to show the incorrect setting of radar measurement range and the occasional missing of line image ce eee ence cence ence teen eens 99 viii Fig 8 2 The incorrect setting on radar measurement range changes the image size from that in the thin white dotted box to that in a much thicker black dashed box The occas
23. t 1 66667s domain size 640x640 m a Directional spectrum b line spectrum directional spectrum and the line spectrum Fig 5 10 are all almost the same as those obtained from the middle grid size 640 x 640 m Considering the radar image resolution at 600 m away from the radar center a raw image resolution is less than 5 m and thus the middle grid size is selected for later analysis 63 a 021704 h18 DONT ance cae dian TOS ee ns g e Meas ries Freq hz 150 100 50 0 50 100 150 Direction deg b 021704 h18 E m hz 0 0 1 0 2 0 3 Freq hz Fig 5 10 Results from radar images analysis on 18 00 Feb 17 2004 with x y 8 m t 1 66667s domain size 1024 x1204 m a Directional spectrum b line spectrum For the moderate sea the significant wave height H 2 m at an offshore National Buoy Data Center station CHLV2 see Chapter 6 the radar images obtained on 10 00 Feb 19 2004 still show a clear large wavelength Fig 5 11 and the analysis results Fig 5 12 using the middle resolution grid i e 5 x 5 m also show a clear dominant wave at 0 1 Hz that is moving toward 95 This direction is corresponding to the shore normal direction off only by 5 which is 8 counter clockwise from E Actually this wave field represents a combination of 10 s 64 1240 Signal level 5 ta 600 cS 600 1240 Y m 5 600 320 320 0 X m Fig 5
24. time in this study f represents frequency The above definition is for an infinite time series For practical applications with a finite length of discrete data a Fast Fourier Transform FFT algorithm was invented a long time for a reasonable number of data point n varies from 256 to 4096 i e n 2 andk 8 to 12 This algorithm was implemented in Matlab as a function called FFT M Notice that the variable t in Eq 4 1 can represent any physical 31 parameter for example spatial distance x or y Because the exponential component ift should be a non dimensional parameter and thus it is obvious that f is frequency if t is time The output of calling FFT is an 1 D complex array i e F f R f iG f where R and G are the real and imaginary part of F with the same length as that of the input time series The dot product of this complex array with its conjugate i e R G is defined as the energy spectrum with a unit of m hz The frequency resolution is given as 1 nAt where At is the time interval of water surface elevation samples An example of an artificially generated time series of 1024 points for water surface elevations with 12 wave components and At 2 s is given in Fig 4 la The result of calculated energy spectrum is given in Fig 4 1b Notice that the x axis of Fig 4 1b is from 0 to a maximum of 1 At 0 5 Hz in this example This is just for the convenience to plot the FFT results quickly Actually the
25. turn itself off using a free software Quick Shutdown Onset Micro Controller e p Model TFX11 D1 D2 D3 T l 1 1 2 Nais TF2_12V l l l i Once 1 gt DPDT Telcom Same as Same as 5V to 12V Relay g LleTtbox i TED lt converter l idl 100 mA 5V Standby power PC power Radar power Radar standby From PC switch switch switch Fig 2 5 Scheme diagram of the PC and radar auto control 14 2 5 Available High speed ADC Interface Devices At the time of this report writing Fall 2005 there are four available high speed ADC devices available on the PC market CompuScope 12100 from Gage Applied Technologies Inc PCI 9820 from ADLINK Technology Inc UF2 3020 Strategic Test Corp and Handyscope 3 from TiePie Engineering These four devices all have a 12 bits maximum ADC rate meets or exceeds 100 Million Samples second MS s The reason of having a minimum requirement on the ADC rate of 100 MS s is not the ADC rate itself but to have a high enough bandwidth for not distorting the radar signals The radar signals that transferred from a radar antenna to the radar control and monitoring unit is an Intermediate Frequency IF signal with a frequency on the order of 10 Mhz In order to maintain a high fidelity after feeding the IF signals into the ADC device a high enough ba
26. 04 b01 are the header file and the image file created on January 12 2004 01 00 The contents in the header file i e the setup of A D interface card date and time radar operation conditions efc are in ASCII format and can be seen by using any text editor The image file however is a binary file and can only be read by using a computer program Anyway these two data files will be moved to another hard disk for storage The last command is an auto shutdown command It will turn off the PC and wait for the next turn on given by the micro controller Notice that the radar data analysis program is not included in the batch file at this time But it can be added later easily once an operational decision has been made 3 3 Signal wires for trigger and radar images In general a marine x band radar usually uses the same antenna for transmitting and receiving signals These two kinds of signals are quite different in terms of power level The transmitted signals usually have a power on the order of 6 to 75 Kilowatt 22 KW for the x band marine radar On the other hand the received signals can be as low as milliwatt Thus a signal amplifier is needed to boost the received signal In order to prevent the strong transmission signals to destroy the receiving amplifier two devices called duplexer and limiter were installed between the antenna and the radar manufacturer s receiving amplifier Fig 3 1 The duplexer chan
27. 1 2004 for wave analysis fics 2 ode ness NEn i a O AEEA EE EEE 69 Fig 5 16 Radar measurement results on 00 00 Feb 21 2004 a directional wave spectrum and b line spectrum ccssssssssssesreeessssssssrrererrrereeseseen 70 Fig 5 17 Averaged radar images at the Virginia Beach a For a relatively severe sea on 18 00 Feb 17 2004 to show two wave breaking lines on the left hand side and b a relatively calm sea on 21 00 March 2 2004 Two offshore buoy sets from the Rudee Inlet are much clear for the calm Sea ccc ccc cece cence ec enee enna aeons T2 Fig 5 18 Averaged radar images at the Virginia Beach on 21 00 March 19 2004 to show signals that are not understood at this time Two wave breaking lines on the left hand side and a trench are also clearly SeeN 0 cece cece ence eee e teen eeeaeeees 73 Fig 6 1 Location map for the X band radar the star wave gauge tripod and the NOAA Station CHLV2 Distance between the radar and the tripod is approximately De Wil 2nd Ga ete ee wach eee eae ees ee ae one ee teeta oe eax 75 Fig 6 2 The star wave gauge a On the moment of deployment b coordinates for wave spectral analysis P1 P2 and P3 represent the location of pressure sensors The center of tripod was selected as the origin Each sensor was located 0 66 m above thescabed crctucn cyranetarcarharauteuy EN e a E e eaS 76 Fig 6 3 Time averaged water surface elevation during the period of m
28. 2 83 m direction 100 deg and a finer spatial resolution x y 5m a Directional ambiguity problem remains for short period waves with a large 47 At 1 6667 s b When reducing At 1 25 s the direction ambiguity problem disappeared 4 3 A Given Random Wave Field It would be nice to check the program developed in the previous section with images of clearly known random sea This is not a simple task however and a month long attempt to generate this kind of images was not successful and thus gave up at the early stage Fortunately a software package DIrectional WAves SPectrum DIWASP developed at the Center for Water Research University of Western Australia Johnson 2005 was available later and used successfully to generate this kind of signals An example of the DIWASP generated images for random sea is available on the VIMS web site http www vims edu physical projects diwasp for showing the nature of random sea The 64 consecutive random sea images used for checking the 3 D FFT program given in the previous section specified a significant wave height of 2 83 m frequency at the peak energy 0 1 hz moved toward the positive y direction Fig 4 12 In other words the major wave direction was 90 degrees from the x axis Other parameters were specified as directional spreading 10 degrees noise level 25 with a range from 0 to 100 water depth at the image site 26 m time interval between two consecutive images
29. 2000 operation system is considered as a sufficient PC for the task An IDE hard disk with a capacity of 100 to 150 GB is required for handle the huge data size Memory with a size of 512 MB would be appropriate One critical requirement for the PC is that it should only has one PCI device usually it is the high speed ADC interface card installed in the PC An AGP graphic interface card should be used instead of a PCI graphic card This is to avoid the possible delay interference of data transfer between the high speed ADC card and the memory or 12 the hard disk Although the delay interference of data transfer is not always happened radar image will be corrupted once it was triggered This phenomenon did not happen when our system was first installed but it happened during the field experiment and took about 6 months to identify this problem Since the data transfer speed for an electronic device e g computer memory is much faster than that for a mechanic device e g hard disk a hard disk with a large buffer memory is necessary Currently a hard disk with 8 MB buffer memory is not uncommon and thus suggested for the wave observation system If this condition can be met then other disk specifications would be immaterial It is worth to note that the temperature range during our experimental period may be severe enough to cause the selected hardware not functioning properly For this reason one should be aware that when the ambie
30. 400 0 2000 100 0 1000 2000 i rdo21704 418 8 2000 ame a gt 1000 i 0 200 100 0 1000 2000 i x m Fig 5 1 A radar image with relatively severe sea Sa 410 obtained at the Virginia Beach on 18 00 Feb 17 2004 a Image from raw data b image after a process to reduce distance effect 53 1200 800 400 2000 o 2000 1000 0 1000 10 2000 6 m 6 1000 4 0 2 2000 1000 0 1000 2000 x m Fig 5 2 A radar image with relatively severe sea S 404 obtained at the Virginia Beach on 08 00 Feb 18 2004 a Image from raw data b image after a process to reduce distance effect This process is particularly helpful when the sea severity is low For example on Feb 19 2004 10 00 the raw radar image Fig 5 3a just barely shows the swells After taking the one 54 third power on the raw signals the swells are clearly shown Fig 5 3b Notice however if the sea is calm then this approach cannot help too much For example the radar raw image on a calm sea on March 2 2004 21 00 Fig 5 4a hardly shows any wave clearly and the processed image Fig 5 4b also cannot show a clear wave pattern fia 1200 2000 1000 0 1000 2000 021904 H10 10 2000 b 6 E gt 1000 7 4 0 pA S 2000 1000 o 1000 2000 z x m Fig 5 3 A radar image with relatively calm sea S 120 obtained at the Virginia Beach on 10 00 Feb 19 2004 a Image from raw data b ima
31. 50 0 05 0 1 0 15 0 2 0 25 0 3 0 35 Frequency hz Fig 4 10 Linear wave spectrum obtained by integrating the f O spectrum for the regular wave images with T 10 s and H 2 m Table 4 1 Test results for monochromatic wave trains with a given H 2 83 m Period s Angle deg H m Error 5 100 1 12 60 6 7 8 9 10 12 14 45 130 60 45 90 130 135 3 02 2 42 294 2 35 2 84 2 71 3 02 6 7 14 5 3 9 17 0 4 4 2 6 7 46 For 5 s waves at the deepwater condition the wavelength is 39 m Thus the 9 9 m ie eT spatial resolution and 1 66667 s temporal resolution may not be good enough By reducing the spatial resolution i e changing Ax and Ay to 5 m but maintaining At 1 66667 s the calculated Hs improved to 1 94 m but directional ambiguity problem remained because of the large At Fig 4 11a When increasing the temporal resolution with a smaller At 1 25 s the directional ambiguity problem disappeared Fig 4 11b This is a clear indication that a fast rotating antenna should be used if the expected wave period is small at a radar observation site Also the higher the temporal resolution the better the results for short period waves 0 3 N Freq hz O T o D o 2 Freq hz o O gt y 150 100 50 0 50 100 150 Direction deg Fig 4 11 Directional spectrum obtained from analysis of the regular wave images with T 5 s H
32. An internet call can be sent out from any PC by using a software WaveOnLanGui exe which is available at http gsd di uminho pt jpo software wakeonlan For the convenience this software is also included in the attached CD When using this software one needs to know the host PC s MAC address as well as the host PC s IP address and the Subnet Mask address Fig 7 1 Please note that the addresses given in Fig 7 1 are only good for the PC used in this project and these addresses are not valid anymore Wake On Lan Magic Packet MEP Help Mac Addess NOE 07 84E C323 Irteinet Address fi 39 70 8 105 Subre Mask 255 255 255 0 Send Mnlinns Internel v Ramot Pot Number E BawakeMel p es Fig 7 1 The window generated when running the program WaveOnLanGui for WOL 93 In order to get MAC address it is necessary to run a Windows program tpconfig exe available in Windows 2000 operation system This program is usually available under the subdirectory system32 When running this program one needs to type in ipconfig all under the DOS prompt The 12 digit physical address in the results Fig 7 2 is the MAC address IP and Subnet Mask address are also included in the results Command Prompt Windows 2666 IP Configuration Hox Name gt s s os e See ere WZ Primary DNS Suffix campus vims edu Node Types cece die Se ie eee IP Routing Enabled
33. FT when the frequency is far below the Nyquist frequency Only these frequencies that have a noticeable energy E ratio gt 0 2 are plotted 39 Fig 4 6 A plot of directional wave energy distribution at a high frequency band to show that the direction ambiguity problem remains when closing to the Nyquist frequency 0 5 t 0 25 hz The energy in the 4th quadrant is the false signal 40 Fig 4 7 The first image of a 10 s monochromatic wave trains was generated with H 2 m and goes 45 degrees from the X aXxiS c cee eeee ence ence eeee eee eeneeenaeeeee 42 Fig 4 8 Translation of wave energy distribution in the kx ky plane into k O plane is the first step to show the 3 D FFT results in one plot Dots in the k O plane are the locations of all available data after translating from the kx ky plane The uneven data space in the k O plane calls for a new data grid with equal space in k and 0 coordinates 3 455 07 acrtisionhs ua oE EA ETE sankey RAE E SE AA E VOER OENE 43 Fig 4 9 Directional spectrum obtained from analysis of the regular wave images T 10 s H 2 m direction 45 deg a k O spectrum b f O spectrum 44 Fig 4 10 Linear wave spectrum obtained by integrating the f O spectrum for the regular wave images with T 10 s and H 2 M ssssssssssssserressrerrrrresssrsssesrrere 46 Fig 4 11 Directional spectrum obtained from analysis of the regular wave im
34. Project Report X band Radar Wave Observation System Submitted to Minerals Management Service U S Department of the Interior 381 Elden Street Herndon VA 22070 By Jerome P Y Maa Ph D and Ho Kyung Ha Virginia Institute of Marine Science College of William and Mary Gloucester Point Virginia 23062 December 2005 Marine X band Radars for Wave Observations Table of Content ices veisdeusueiostestovere te ees eey eae pestle te ives ce ato ates ii Tablet FIoUTC eiai N N a A E N AE N E ONR ASE iv Chapter 1 Introduction 2 25 icesc 2 ebstibeosnt welacenoee Aveeetaaie EE a EE 1 Chapter 2 Hardware Considerations c cece cece ence ence eeeeeeneeeeaeeeeeeenes 5 2A X band RACAL 240 255 tase ube sS eee sd rE E aE A ASEA TEE a RIR E 5 2 2 Basic Characteristics of Radar Images eee ee eee e eee eee ne eee ees 9 2 52 Personal COMpuUter 2520210 dincedseonisdb eadesedea hoki be serinin erai dennie 12 24 WHETO COMMONEL ix accors ees auch fu aucun KEROT AEA EE Vera ces genes weenie 13 2 5 Available High speed ADC Interface cece eee e eee e eee e eee eee en 15 2 6 Selection of ADC Rate s ivisc essei savag vai del See ee 16 Zier SLIMY OME ter Cn aiyes a e e e uae weno wee E E a Oret 18 Chapter 3 Data Acquisition s sssssscersssssssseserrreissrresssrrererrresessresserrecee 19 Sele System Control geesaycevedeosawaces e Enee EE E ARESE RTRA 19 3 2 Batch File for PC Programs Control
35. TA was used to do this task After using GRIDDATA however one would find that wave energy at a few grid locations mainly with a low k coordinate and when the 8 coordinate is close to 0 or 360 degrees are specified as nan which stands for not a numerical value This phenomenon was caused by not having an enough spatial resolution for interpreting wave energy at low k values see Fig 4 8b without data on the negative 9 coordinates and without data with a O coordinate that is large than 360 degrees respectively A simple treatment of this problem would be replacing the nan with zero This treatment is efficient and quite good for coastal wave observations Hm 800 1 0 8 0 oo D nH oOo oOo a DISTANCE Y m N m 0 1 J 200 400 600 800 DISTANCE X m Fig 4 7 The first image of a 10 s monochromatic wave trains was generated with H 2 m and goes 45 degrees from the x axis 42 0 2 a Summation of all frequency p k k 0 1 ky 1 m 0 1 CART2 POL k nv oo Oo oO 28 a KJ to ta uo Fig 4 8 Translation of wave energy distribution in the kx ky plane into k O plane is the first step to show the 3 D FFT results in one plot Dots in the k O plane are the locations of all available data after translating from the kx ky plane The uneven data space in the k 9 plane calls for a new data grid with equal space in k and 0 co
36. ad 128 points in both the x and y directions respectively with Ax Ay 7 m In time domain 32 snap shots were generated with At 1 66667 s The deep water condition was used again for this example After calling FFTN the results of adding up all the 32 frequency bands kx ky are given in Fig 4 8a The spike because of the monochromatic waves in the first quadrant of this sub plot shows that the wave direction is 45 degrees The dashed circle indicates that the wave number k 0 5 m This sub plot has a Cartesian coordinate system with data point on a grid with equal intervals in the kx ky plane i e Ak Aky 277 128 7 m Knowing that kx k cos and ky k sin 9 all the values on each grid point of this Cartesian grid can be translated to have a polar coordinate k 9 grid A Matlab function CART2POL M can be used to do this job Notice that the energy value at each grid point also changed because of the coordinate change and the following equation was used Young et al 1985 p k 0 k oC kx ky 4 6 41 where o k 9 is the wave energy distribution in k 0 plane Locations of these new grid points in the rectangular k 0 plane Fig 4 8b show that the distances among points are not the same and thus a new grid with equal space in Ak and 49 respectively is needed This requirement calls for interpreting the energy values at each new grid point for the rectangular k 0 plane A basic Matlab function GRIDDA
37. ages with T 5 s H 2 83 m direction 100 deg and a finer spatial resolution x y 5m a Directional ambiguity problem remains for short period waves with a large At 1 6667 s b When reducing At 1 25 s the direction ambiguity problem disappeare diserna A E E E A E teaees 47 Fig 4 12 First image of a series of random wave fields generated by using DIWASP package with peak wave frequency fp 0 1 Hz Hs 2 83 m travel toward the positive y axis direction 2 nos bien Laude oo dt a che etdgeenin aeetne votes denen anseetaenebedleess 49 Fig 4 13 Results from 3 D FFT in kx ky plane to show the directional spreading at a frequency band close to the given peak energy frequency for the random sea generated by using DIWASP iii 30s c53 cavdss cae bvs cased cncavccudceueessgeueVendanedeseseevees 50 Fig 4 14 Comparison of directional wave spectra a Analyzed from the random sea images generated by using DIWASP b the given input spectrum 50 Fig 4 15 Comparison of the analyzed line spectrum for the given random waves iaat AEE ORR ener ote TOR Oe Vir Rec eee a oe UI Rin en eae ee ye NE RON 51 Fig 5 1 A radar image with relatively severe sea Sa 410 obtained at the Virginia Beach on 18 00 Feb 17 2004 a Image from raw data b image after a process to reduce distance Cle ts 232d es dos ced he tis band coe eo Mak oad AN Se ican hdd oe hb is dee Sees 53 Fig 5 2 A radar image with relatively s
38. and J Wolf 2000 Tide wave and suspended sediment modeling on an open coast Holderness Coastal Engineering 41 237 267 Ruessink B G P S Bell I M J Van Enckevort and S G J Aarninkhof 2002 Nearshore bar crest location quantified from time averaged X band radar images Coastal Engineering 45 19 32 Wolf J and P S Bell 2001 Waves at Holdrness from X band radar Coastal Engineering 43 247 263 Wyatt L R S P Thompson and R R Burton 1999 Evaluation of high frequency radar wave measurement Coastal Engineering 37 259 282 Wyatt L R J J Green K W Gurgel J C Nieto Borge K Reichert K Hessner H Gunther W Rosenthal O Saetra and M Reistad 2003 Validation and intercomparsions of wave measurements and models during the EuroROSE experiments Coastal Engineering 48 1 28 Valenzuela G R 1978 Theories for the interaction of electromagnetic and ocean waves A review Boundary Layer Meteorology 13 61 85 Wu L C D J Doong C C Kao and C M Tseng 2005 Wave and Current Fields Extracted from Marine Radar Images Proceedings of the Fifth International Symposium on Ocean Wave Measurement and Analysis WAVES 2005 paper No 15 Jul 3 7 Madrid Spain 2005 107 Young I R W Rosenthal and F Ziemer 1985 A three dimensional analysis of marine radar images for the determination of ocean wave directionality and surface currents Journal of Geophysical Research 90 C1 1049 1059 108
39. and the limitations on this kind observation system In Chapter 2 the considerations on hardware are presented Details on how to select a proper marine radar and other associated hardware are documented Thus it is possible to extend and improve for future uses In Chapter 3 details of the radar image data acquisition system are presented The principle of system control and data acquisition software is explained In Chapter 4 the principal of wave spectrum analysis is presented It starts with the basic one dimensional 1 D Fast Fourier Transform FFT and then advances into two dimensional 2 D and three dimensional 3 D wave spectrum analysis Clearly known signals are used to demonstrate the process of this technique The numbers acquired in radar images however do not represent water surface elevations These numbers are also distorted because of the nature of measurements Thus extra processes are required before using the 3 D FFT process for analyzing wave characteristics These processes are presented in Chapter 5 Although the wave energy directional distribution and wave period at the peak frequency can be obtained by following the technique given in Chapter 4 and the image process procedures presented in Chapter 5 the significant wave height has to be calculated by using the Signal Noise Ratio SNR and thus require calibration In Chapter 6 the details on calibration by deploying a star wave gauge and using the results
40. ar system mentioned in Chapter 3 was setup at the roof of the Clarion Resort and Conference Center 36 30 036 N 75 34 935 W Fig 3 5 with an elevation about 38 m above the sea surface The shoreline which will be used as the x axis in radar image process at this location has an angle about 13 degrees West from North and this information will be used later for determine wave directions For example waves coming from E will be shown as waves coming from 77 90 13 counted from the positive x axis This is equivalent to say that waves are going toward 103 from the radar analysis results An example of the radar image Fig 3 6 shows that a clear radar wave image can be obtained Notice that the wave image quality is better at the center and gradually degraded on the two sides that are close to the shoreline This is possible because of the radar wave direction is parallel to the wave crest lines In other words the strong wave reflection from a rising slope do not return back to the radar because of the nearly parallel of radar wave incident line and the wave crest line The jetty on the north of the radar site the two breakwaters at the Rudee Inlet and the wave breaking line can be seen 27 clearly in this image At the bottom center the solid red semi circle marks the blind zone l Radar Location ji Roof of Room 1201 Clarion Resort and Conference Center lt Fig 3 5 The field experiment si
41. ary process within the selected sub domain The last condition is a basic assumption of using FFTN and it means the wave characteristics e g wave period wave height efc should be the same or near the same for the entire sub domain In general this assumption is not a problem for ocean waves because of the deep waters and thus water depth plays no role in wave transformation and within a radius of 2 5 to 5 km this assumption held quite well For coastal waves wave characteristics change when approaching the coast This posts a major limitation on the size of sub domain Considering the image distortion caused by side lobe effect for the near field the image within a distance of 500 m from the radar center shall not be used unless corrections can be made For the purpose of insurance for not using distorted image selection of a sub domain that is 600 m away from the radar center would be better Because of using a rectangular sub domain another limitation on the maximum distance would simply means the maximum distance is about 200 m less than the maximum radar sensing radius If using 128 x 128 points for a rectangular sub domain at 600 m away from the radar center and considering a rectangular image resolution of 3 5 and 8 m the size of the sub domain would be 384 x 384 m 640 x 640 m and 1024 x 1024 m respectively Two factors i e minimum wave period and maximum wave period should be considered when selecting the size For a
42. cords of significant wave height at Stas CHLV2 a February b March c April d November and e December 2004 86 d CHLV2 2004 Nov Beers E PEREA e CHLV2 2004 Deg van Hs m TIME day of December Fig 6 11 Continue 6 5 Signal Noise Ratio SNR from Radar Images In general SNR is a parameter to judge the quality of an electronic device for performing a particular function For example the higher the SNR of an amplifier the better the quality of this amplifier Here two different definitions of SNR are available for converting the radar measured SNR to Hs The first definition of SNR was given by Young et al 1985 as the ratio of the energy at the spectral peak to the background energy level well away from the dispersion shell The second definition is specified by Borge et al 1999 as 87 SNR F k k f dk dk df F k k f dk dk df 6 1 Q b where the integration domain Q represents a selected finite thickness of the dispersion shell discussed in next section and the other integration domain b stands for the background These two different SNR will be checked for their use for converting SNR to Hs The dispersion shell is an imaginary shell in 3 D display of the dispersion relation o gk tanh kh with kx and ky on the horizontal plane and o 27 f on the vertical axis In 2 D plot the shell will be collapsed on the kx
43. d After the course of this study the possible improvements on hardware the limitations of X band radar wave measurement systems and the other features that have not been addressed yet are presented in this chapter Finally the conclusions of this study are presented 8 1 Improvements needed on hardware During the course of checking details of the X band radar wave observation system the major difficulties are the understanding of hardware limitations and the verifications of analysis results Most of the understandings of hardware requirements are given in Chapter 2 and others are discussed here Stability of Antenna Speed This is a rather critical factor to ensure the accuracy of the system In theory successive radar scans should yield images with each pixel having exactly the same physical locations In other words the location of any pixel in one image should be the same as the location of the corresponding pixel in other images Marine radars however may not have this requirement because there is no need to examine consecutive images and thus a radar antenna may not point to exactly the same angular position during each revolution When using radars to get consecutive radar images for 3 D FFT however this requirement is important A high precision gear motor and sufficient power supply are needed to meet this requirement Minimize Hardware Interference As pointed out early the interference between the PCI graphic card and t
44. e the image became thick as that marked by the black dashed box This problem is an error of operation and thus documented to prevent it happens in the future 8 2 Limitations A major limitation is caused by the antenna rotating speed of marine X band radars The maximum speed determines the temporal resolution Because the Nyquist frequency is about 0 3 Hz Png 1 2At and At 1 6667 s any signal that is larger than 0 25 Hz cannot be trusted The analysis using clearly known signals given in Chapter 4 also demonstrate that directional ambiguity problem remains when the frequency is close to the Nyquist frequency The spatial resolution of radar images limits the selection of a sub domain which should not be too far away from the antenna A reasonable radius distance would be between 0 6 and 2 5 km if the antenna elevation is high enough If the antenna elevation is low e g less than 10 m then the radius distance will be reduced significantly e g 101 0 2 to0 5 km This limitation however may be utilized for different project More will be discussed later In this project the radar was installed on the roof of a tall hotel building and thus the foundation is stable If a slender tower is necessary to mount the radar then the movement of radar under bad weathers may cause more image distortion If that is the operation condition more attention should be paid to the foundation structure The currently available meth
45. e conditions are the same Possible relationship among radar measurement results wave propagation direction and radar beam direction should be also checked These subjects would be the targets for next phase study 8 5 Conclusions 104 Using marine X band radars for wave measurements and others is a promising remote sensing technique This is because of the versatility of this device and the advance of personal computer and high speed ADC devices For the X band radar set up used in this study there is a limitation on temporal lt 2 Hz and spatial resolution gt 8 m For offshore uses of this technique a small X band radar 6 kilowatts may be the choice Experience on calibrating the X band radar installed at Virginia Beach indicates that it is impossible to get a perfect correlation between the Signal Noise Ratio SNR and the significant wave height More comprehensive calibrations are necessary to clarify the reason s of a scatter correlation between these two parameters Other wave analysis techniques that can be used for radar image analysis should be first checked with a mathematically generated wave fields 105 References Alpers W and K Hasselmann 1982 Spectral signal to clutter and thermal noise properties of ocean wave imagine synthetic aperture radars International Journal of Remote Sensing 3 423 446 Bell P S 1999 Shallow water bathymetry derived from an analysis of X band radar images of waves
46. e conditions at an offshore site of the Virginia Beach during the Spring of 2005 The objective of this deployment is to provide ground truth of wave characteristics for converting the Signal Noise Ratio SNR obtained from analyzing X band radar images to the significant wave height H The correlation between wave heights measured at a NOAA station CHLV2 located about 25 km offshore of Virginia Beach and an Engineer Research and Development Center ERDC wave station VAO01 right offshore of the Rudee Inlet was also made for calibrating the radar measured SNR 6 1 Star Wave Gauge The star wave gauge was deployed at 36 50 116667 N 75 57 8666 W off the City of Virginia Beach Virginia with a mean water depth of 8 2 m The distance between the wave gauge and the X band radar was approximately 570 m Fig 6 1 A star wave gauge has three pressure gauges mounted on the tips of a tripod base 0 66 m above the seabed Fig 6 2 Diver observation determines the orientation of the tripod after deployment Each pressure transducer was connected to the data logger house by using a underwater cable and connectors The pressure transducers were manufactured by Druck Inc model PDCR130 Two different ranges 15 psig and 30 psig were used because of the availability These transducers have an accuracy of 0 1 of their maximum reading thus with an accuracy of 1 03 cm and 2 06 cm respectively 74 X band Radar Wavegauge Rudee
47. easurements This indicates a mean water depth of 8 2 m ec cee eee eee ee 78 Fig 6 4 Time series records from the wave gauge a significant wave height Hs the arrows indicate when a detailed spectrum analysis was given in Fig 5 6 b peak wave period c Dominant wave direction d direction of the peak period 79 vii Fig 6 5 Wave roses for the period from 11 00 March 16 22 00 April 6 2005 a Direction of wave period at the peak energy and b dominant wave direction 80 Fig 6 6 Wave condition on 1 00 March 18 2005 a Directional spectrum b HINES Pe CU WE sey asec eee ates gee a aw eo eee ee we ee 81 Fig 6 7 Wave condition on 16 00 March 23 2005 a Directional spectrum b lime spectr ni es fsawacs steenssiesee set sou reibesehatanasxews eaves eeea civ egeasea tte 82 Fig 6 8 Wave condition on 10 00 March 28 2005 a Directional spectrum b WME SPECHOUIMN occiucscvanenchemew REEE ees ceca ENARE ETRE NETRE EENE AEE E 83 Fig 6 9 Wave condition on 16 00 April 2 2005 a Directional spectrum b line spectr M rsen ce wen sees Lenses end ema ven ke vou AE EE aa eaaa 84 Fig 6 10 Relationship between the significant wave heights at Stas CHLV2 and Fig 6 11 Records of significant wave height at Stas CHLV2 a February b March c April d November and e December 2004 cece cece eee eee 86 Fig 6 12 Example to show a collapsed dispersion
48. een the better observation range and the radar elevation Fig 2 3 indicates that at least 30 m is necessary If the radar antenna can be oriented a little off horizontal and the maximum EM wave direction can be pointed toward the sea level at a far away distance then the better working range may be extended for example up to that showed by the 0 5 line in Fig 2 3 Although this is still a hypothesis it may worth to check out in the future study 1 4 Ra 4 1 E a anol ay f E Pa Roz Pa o Pa Am 4 0 5 Oo Cc G o _ Cc lt 5 L E i i l i 0 1000 2000 3000 X Distance m Fig 2 3 Relationship between radar antenna height and the better working area Ly is for an impinge angle of 1 and L is for a possible extension of the better working area by increasing the impinge angle to 0 5 2 2 Basic characteristics of radar images Assuming that the sea clutter noise is still larger than the background white noise at a distance 5 km away from the radar Thus a maximum observation radius of 5 km was selected to show the characteristics of radar images collected Later these characteristics are also useful for helping determine the proper Analog to Digital Conversion ADC rate The time for radar waves to travel along a beam should be first estimated For a 5 km distance it means a two way travel distance of 10 km Since the Electrical Magnetic EM wave speed is 2 99792 x10
49. ement site is too complex to void the assumption that the wave field is stationary For example if wave diffraction or refraction process is strong then the traditional FFT procedures cannot be used In that case wavelet analysis should be used Doong et al 2001 2003 The other possible option to overcome this difficulty is to reduce the size of the selected sub domain e g from 128 x 128 points to 64 x 64 points and increase the number of images for FFT e g from 64 images to 128 images Although this option has not checked yet it is based on the understanding that wave diffraction and refraction is a local effect and a smaller sub domain should have a smaller impact caused by local effect 8 3 Other Features With the limited resource only details of the wave measurement portion of a X band radar wave observation system are scrutinized It is documented however that tidal current fields and the bathymetries can also be measured by this remote sensing technique Bell 1999 Prandle et al 2000 Kobayashi et al 2001 Gangeskar 2002 Lee et al 2005 Wu et al 2005 Studies of the dynamic of nearshore bar crest locations using a marine X band radar was conducted by Ruessink et al 2002 A study on sand bar movement by using a small radar 6 kw is under developing by McNinch personal communication The above statements demonstrate that there is a great potential of this remote sensing technique Besides the above menti
50. ented direction is for wave propagation direction ceeeeeene cent eeenes 62 Fig 5 9 Results from radar images analysis on 18 00 Feb 17 2004 with x y 5 m t 1 66667s domain size 640x640 m a Directional spectrum b line spectrum 63 Fig 5 10 Results from radar images analysis on 18 00 Feb 17 2004 with x y 8 m t 1 66667s domain size 1024 x1204 m a Directional spectrum b line SIS CULUM os sera cies a0 e r e wae w aye oe tne E whe Ree aA Aah E EE S 64 vi Fig 5 11 First three rectangular radar images on 10 00 Feb 19 2004 for wave analysis With x y 5 m t 1 66667 s domain size 640 x 640 m 65 Fig 5 12 Results from radar images analysis on 10 00 Feb 19 2004 with x y 5 m t 1 66667 s domain size 640 x640 m a Directional spectrum b line Jena i o n hac ven is ct acsaawonwe sige tiaes suse aaaenearmnensdoeerey ce Nannie benmeernicebanzaaeeneeds 66 Fig 5 13 First three rectangular radar images on 21 00 Mar 2 2004 for wave analysis With x y 5 m t 1 66667 s domain size 640 x 640 m 67 Fig 5 14 Results from radar images analysis on 21 00 Mar 2 2004 with x y 5 m t 1 66667 s domain size 640 x 640 m a Directional spectrum and b line SPCCU UN wacnlas te Giese shh avendse te E a es Mameuleady ah Maud dete ah bat cults 68 Fig 5 15 First three interpreted rectangular wave images measured on 00 00 Bebe 2
51. esented in Fig 5 5 This figure indicates that a minimum sea severity about 120 is necessary to do the rest analysis In future operation if S does not meet this minimum or a later revised value then a calm sea may be concluded immediately and the system can shut down immediately to save battery energy 5 3 Interpreting Radar Image for a Smaller Rectangular Domain The next process is related to the FFTN requirement Data used by calling the FFTN must be in a rectangular domain with evenly spaced Ax and Ay The selection of this rectangular domain size and the size of Ax and Ay also need to be clarified and that is the objective of this section Because of the nature of radar scanning radar data are presented in polar coordinates and that is why all the radar images presented so far are all having a semi circle shape Converting the raw data with polar coordinates and uneven spatial resolution to a data set with 57 rectangular coordinates and even spatial resolution is necessary to use the standard algorithm for 3 D Fast Fourier Transform routine FFTN Average Radar Signal Strength 18 20 22 24 26 23 Time day of February 2004 Average Radar Signal Strength Time day of March 2004 Fig 5 5 Average radar signal strength during a February 2004 and b March 2004 58 The size of the rectangular sub domain depends on the resolution of radar image the raw radar image size and the suitability of a station
52. evere sea Sa 404 obtained at the Virginia Beach on 08 00 Feb 18 2004 a Image from raw data b image after a process to TEAUCE GIStANCe IEC Ecce titie sce hee a a Seca Aig lees a5 Arte nabs ad 54 Fig 5 3 A radar image with relatively calm sea Sa 120 obtained at the Virginia Beach on 10 00 Feb 19 2004 a Image from raw data b image after a process to TEGUCE distance effectis meene Sava ah ss wav leew s was e Datars eS Sand aoe wey wed rea Bae 55 Fig 5 4 A radar image with relatively calm sea Sa 105 obtained at the Virginia Beach on 21 00 Mar 2 2004 a Image from raw data b image after a process to reduce distance effects E ck eie oes hedek son cowie cles ved covacuitelsenceusdeules e es cobecule es 56 Fig 5 5 Average radar signal strength during a February 2004 and b March 2004 peal acs ate Dac hide Una Site E Ua ak ahd oth E oe ol fu w lhe ties esas ao 58 Fig 5 6 Location map to show the measured image location and the interpreted location for wave ANALYSIS s lt oi02 50edeacniesnscenspvewiwna ned pede dele sa ewdebenigders ond eneeseehe 60 Fig 5 7 First three rectangular radar images on 18 00 Feb 17 2004 for wave analysis With x y 3 m t 1 66667s domain size 384 x 384 M 068 61 Fig 5 8 Results from radar images analysis on 18 00 Feb 17 2004 with x y 3 m t 1 66667s domain size 384 x 384 m a Directional spectrum b line spectrum The pres
53. follows F f k n t xe te dtdx 4 2 where x represents a series of spatial locations in unit of m at where water surface elevations were measured Because kx must be a non dimensional parameter k must 33 have the dimension of m For the convenience of using trigonometric function a coefficient of 27 is included in the definition of k i e k 27 L where L is the wavelength Notice that there are two dummy variables in Eq 4 2 and these two can be changed as t and y or x and y In cases that x and y are selected as the two dummy variables then the resulting function is F kx ky where the subscripts x and y are added to represent wave number components in the x and y directions respectively Similar to that for the 1 D FFT a function for 2 D FFT for a finite length and discrete domain FFT2 M is also available in Matlab An example of using this function with an artificial signal is given next A snap shot of a wave field n x y was generated according to the following equation n x y aj cos k cos 0 x kj sin 0j y oj 4 3 with five monochromatic wave trains i e j 5 Fig 4 2 All the wave amplitudes i e ap s were m and the five wave periods were T 4 5 7 8 and 10 s respectively The five wave directions were 8 160 100 60 65 and 0 degrees respectively and the five wave phases were 30 70 50 20 and 0 degrees Deep water condition was assumed and thus the wave number k
54. from a nearby NOAA wave station CHLV2 are presented Remote access of the data and remote control of the system is a convenient and sometimes necessary tool to have a successful long term operation Possible options of remote control using either Local Area Network LAN or a telephone modem are explored The necessary software and hardware were collected and tested Details are given in Chapter 7 Chapter 8 is the discussion and conclusions The problems encountered in this project are discussed Cautions and future works on using this kind of wave observation system are also marked Chapter 2 Hardware Considerations It is well known that inexpensive marine X band radars can be used for wave observations Details on how to select a suitable marine radar and other associated hardware however are not clearly documented and thus it is worth to discuss the details and the criterion for these selections These are the objectives of this chapter 2 1 X band Radar X band radars have a frequency range from 9 41 to 10 5 Ghz Thus the wavelength of X band radars varies from 2 8 to 3 2 cm in air This is a rather important information because this particular wavelength is approximately equal to the ripple wavelength existed on the water surface when the wind speed is more than 3 m s Although the ripple waves are not the target for the measurements they are coexisted with the much large gravity waves which is the target of the measurements T
55. g 90 T T T T T T T 70F 50F E m hz 30F 0 1 02 0 3 0 4 Freq hz Fig 5 14 Results from radar images analysis on 21 00 Mar 2 2004 with x y 5 m t 1 66667s domain size 640x640 m a Directional spectrum and b line spectrum With a significant wave height of about 1 m at the offshore station CHLV2 on 00 00 Feb 21 2004 the radar images Fig 5 15 just barely show the wave pattern and the analyzed directional spectrum Fig 5 16 shows the equally important long period waves 0 1 hz goes to 100 degrees and short period 0 2 Hz waves goes to 40 degrees The line spectrum indicates more energy at the 0 2 Hz frequency band but actually the wave energy at that frequency band are coming from two major directions 40 and 130 degrees 68 1240 Signal 1 leval 600 1240 o 2 wi 600 1240 3 600 320 320 0 X m Fig 5 15 First three interpreted rectangular wave images measured on 00 00 Feb 21 2004 for wave analysis 04h00 ig sees Freq hz o N oO f f f 1 150 100 50 0 50 100 150 Direction deg b 022104 h00 30f 20F E m hz 0 l D1 02 t 03 t 0 4 Freq hz Fig 5 16 Radar measurement results on 00 00 Feb 21 2004 a Directional wave spectrum and b Line spectrum The above three paragraphs indicate that a significant wave height Hs about m at the offshore station CHLV2 would be the m
56. g to distinguish the wave propagation direction for that frequency band k 1 m 0 2 0 1 0 0 1 0 2 k 1 m Fig 4 6 A plot of directional wave energy distribution at a high frequency band to show that the direction ambiguity problem remains when closing to the Nyquist frequency 0 5 t 0 25 hz The energy in the 4th quadrant is the false signal Notice that the above two figures show the energy distribution for each frequency band Actually there are redundant information included in these two figures because kx and ky also include wave frequency and wave direction information if the linear dispersion equation o gk tanh kh is used For this reason the 2 way to present the 3 D FFT results can be summarized in one single plot and that is explained in next section 40 4 2 Given Regular Wave Fields Since the 3 D FFT result is a 3 D matrix that includes information for n frequency bands m kx bands and L ky bands one way to present the summarized results is to add these n frequency bands together to form a single 2 D matrix in kx ky plane This can be done relatively easy by retrieving the energy density in kx ky plane for each frequency band and then add them together with a multiplier of 1 n dt for the true spectrum energy Example of a monochromatic plane wave field i e j 1 in Eq 4 5 was displayed Fig 4 7 only show the first snap shot for this case to demonstrate the process The spatial domain h
57. ge after a process to reduce distance effect 55 y m 030204 H21 1200 a 2000 500 1000 400 j 2000 1000 0 100 2000 o 2000 030204 H21 amp 1000 A 2000 0 x m Fig 5 4 A radar image with relatively calm sea S 105 obtained at the Virginia Beach on 21 00 Mar 2 2004 a Image from raw data b image after a process to reduce distance effect y m 1000 1000 2000 The above information indicates that there is a threshold for using the x band radar for wave observation Itis already discussed in Chapter 2 that a minimum wind of 3 m s is required Here another index average radar signal strength Sa is also useful and more are given in the next section 56 5 2 Average Radar Signal Strength Sa This parameter can be obtained relatively simple and fast After taking the radar images a simple summation of all the signals on all the radar track lines can be obtained This process don t have to use all the images just one or two images would be enough because there is not much change of this information at a time As a matter of fact it was found that all the first three images produce a negligible difference in Sa The values of S for the four cases mentioned in the previous section are also given in the figure captions It can be seen that a minimum S value of 120 to 150 is necessary to see a wave field A summary of S value for the survey period in February and March of 2004 is pr
58. ges to a high impedance device when a strong signal comes to it and thus blocks out the high power signals Because there is a possibility that a signal coming from a near by radar that is not strong enough to ignite the duplexer but strong enough to destroy the amplifier a limiter is usually provided to limit the power that can go to the signal amplifier The duplexer limiter amplifier and rectifier are all provided by the radar manufacturer and thus these are not the concerns of this project The objective of this discussion is to point out where the echo signals can be picked up Further explanation on how to pick up the echo signal is given next Physically there are two units for a marine x band radar 1 the radar antenna and gear head unit and 2 the control and monitor unit Radar waves are actually generated in the 1 unit but the control signals are generated in the 2 unit The echo signals are also detected in the 1 unit but pass to the 2 unit for processing For this reason there is a cable to connect these two units for signals to travel between them Two kinds of signals are needed for the radar image acquisition The first kind of signals is for when to start the ADC The second kind of signals is the radar echo signals that will be digitized All these two kinds of signals are available from a radar control and monitor unit provided by the radar manufacturer see the two dashed lines in Fig 3 1 that c
59. he PCI ADC device interrupted the ADC process and produced 98 useless images at later stage This problem happened after November 2004 and the fatal interference on radar image Fig 8 1 was not recognized until the data analysis process was completed The square sub domain retrieved from the previous figure shows the problem more clearly Because of the occasional missing of radar line images the blue lines in Fig 8 2 it produces a strong signal gradient on the x direction Thus the resulting wave propagation direction after taking FFT is always parallel to the x axis either between 170 to 180 or between 10 to 10 2500 2000 1500 1000 Distance Y m on 3 co 2000 1000 0 1000 2000 Distance X mm Fig 8 1 A raw radar image to show the incorrect setting of radar measurement range and the occasional missing of line image This problem was finally identified as the interference on PCI bus and thus solved by changing the PCI graphic card to an AGP card It is however taking months to identify this problem Actually it is the home made digital radar trigger signal generator 99 that helps to shift our attention from software bugs to hardware interference Before the generator was used there is no firm answer on exactly how many trigger pulses will be generated from the radar for a half circle radar image Thus it is not certain what causes the mis counting problem After switching to the generator
60. he principle of using marine X band radar for wave measurements is using the Bragg effect Valenzuela 1978 to get the scatter waves generated by interactions between radio waves and ripple waves This scatter waves are usually referred as the sea clutter noise from radar s point of view because the scatter waves are not the target of a regular radar system Because the closer the ripple wavelength and the EM wavelength the stronger the scatter wave strength and thus easier for a radar antenna to pick up the scatter waves For this reason x band radar is a better option The other type of marine radar S band radar has a nominal frequency of 2 455 Ghz Because the wavelength is large about 12 cm the scatter waves strength would be weaker and thus the detectable range would be significantly smaller when comparing with that for the X band radar For this reason S band is not suitable for the wave measurement purposes The range of using X band radars for wave measurements is limited by the radar s capability of measuring the scatter waves and thus limited by the available power of X band radars Since x band radar is a commercial product with a few options on the output power e g 2 4 6 10 25 50 kilowatts the cost is reasonable compared with other wave measurement approaches In general the larger the X band radar output power the larger the measurement area and the measurable conditions However it is also true that
61. ho at near field lt 500 m from radar Echoes from breaking wave foams at a distance Lb from the radar exceeds the echo strength at the true distance Lt which is calculated by the EM wave travel speed and the time duration after trig 30 Fig 4 1 Example of a selected time series and the results of calling FFT a n t with 12 componential waves b energy spectrum by a direct dot product of F f and the conjugate of F f and c energy spectrum after taking FFTSHIFT 33 iv Fig 4 2 An artificial 2 D wave image n x y generated from an equation with 5 monochromatic waves with period 4 5 7 8 and 10 s The wave amplitudes are the same but the wave angles 160 100 60 65 and 0 degrees and phases are COU A Ro Uo 0 ia en aca ra ho a et cer ip rare oe tec rl oe ene Ora an Cate eee 35 Fig 4 3 Calculated wave directional distribution using the wave image given in the previous figure Direction ambiguity is associated with this 2 D FFT Energy peaks inside the small circles are the false signals cc cece cence ence eee e eee eeeneeeaeees 36 Fig 4 4 The first and the 30th images of a series of 64 artificial 2 D wave images n x y t generated with the conditions given in Section 4 1 3 cece eee eee ee 38 Fig 4 5 Part of the calculated wave energy directional distribution using the time series of wave images given in the previous figure Direction ambiguity is gone with 3 D F
62. ing approach has the advantage of getting measurements over a large area using only one set of instrument e g an air borne video or radar system If it is a land based system e g a High Frequency HF radar or X band radar the operation cost is relatively inexpensive especially for the X band radar if the required study area is within a radius of 3 to5 km HF radars are mainly used for large area currents and wave measurements Gurgel et al 1999 The instrumentation cost is also big on the order of millions for a system http wwwocean tamu edu GOOS GSCX GSCS_appendix_05 pdf The principal for a HF and a x band radar are the same all use Bragg effect to detect the scatter waves but the selected wavelength are different A HF radar selects large EM wavelength with the frequency range from 3 to 30 Mhz to produce Bragg scatter waves with the gravity waves itself but a X band radar uses short EM waves to interact with ripples on top of the gravity waves The operation range of HF radars is large normally on the order of 50 km and can be extended to 200 km with an antenna array but with a relatively low resolution Although the Hi Res SeaSonde from Codar Ocean Sensors is claimed having the capability of measuring waves the web page cited in this paragraph however stated that other devices are needed for measuring directional wave spectra Unlike HF radars X band radars are widely used for the vessel navigation purpose and
63. inia Beach on 18 00 Feb 17 2004 a All the radar burst lines 1750 are used for image plot b only 437 burst lines are used for the image 29 radar antenna Horizontal Fig 3 7 Sketch to show the image distortion caused by side or side lobe effect when there is a strong echo at near field lt 500 m from radar Echoes from breaking wave foams at a distance L from the radar exceed the echo strength at the true distance L which is calculated by the EM wave travel speed and the time duration after trig 30 Chapter 4 Software for Data Analysis It would be better to start with the principle of wave spectrum analysis and then advance into three dimensional 3 D wave spectrum analysis After the flow of data processing is explained it would be better to use clearly known signals to demonstrate the results of data analysis At last test of the program developed with images for a random sea is presented 4 1 Principle of Data Analysis First the basic one dimensional 1 D and two dimensional 2 D wave spectrum analysis will be given briefly to introduce the concept of Fourier Transform for wave spectrum analysis 4 1 1 1 D wave spectrum analysis A time series record of water surface elevations n t at a particular observation site can be transferred into frequency domain by using the Fourier Transform defined as follows F f n t e dt 4 1 where i 1 tisa dummy variable that represents
64. inimum for radar to pick up meaningful images Further discussion will be given in next chapter Notice that the energy level given in all the spectrum plots are meaningless because the signals used are not water surface elevation The numbers in the signal are just integers that representing the signal strength For this reason the analysis so far can only reveal the wave direction distributions but not the significant wave height The value of Signal to Noise Ratio 70 SNR was suggested Young et al 1985 for interpreting the significant wave height and thus requires calibration That will be given in next chapter 5 5 The Average Radar Image When using a X band radar for wave measurements there are side products that can be used for other purposes For example each radar wave analysis requires 64 images to resolve the ambiguity on wave propagation direction but the average of all images during a measurement time may be used for measuring the bathymetry Leu 1998 and others Here an example is given to show the image of rip current During a relatively severe sea the alongshore current created by oblique wave breaking will find a way to return to the ocean at somewhere This alongshore current can also be bended by a shore normal jetty For example the shore normal jetty at the Virginia Beach located at x 1150 m Fig 5 17 causes the south going alongshore current to bend and returns to ocean This shore normal current may
65. ional missing of line images the blue lines produces a strong signal after FFT and results is that waves are always traveling in a direction parallel to the x LS es Seni ony ctu iw esr E E E syaindamnediineathe saaalayerea nee aw iednenl 100 1X Chapter 1 Introduction Water wave observation is one of the important and difficult jobs that required to be done for many purposes e g shore protection harbor management navigation safety coastal resource management rescue missions efc Traditional approaches for accomplishing this kind of mission include using wave buoys pressure wave gauges acoustic wave gauges airplane or satellite video or radar observation land based HF band radar and X band radar The first three kinds of techniques are well developed techniques for direct observation of water surface elevations or water particle velocities for estimating wave conditions These techniques were first developed and followed the available wave theory mainly the linear wave theory Thus they are prevailed in the wave measurement market These techniques however require the deployment of a sensor or a series of sensor in the water and thus are expense for maintenance In areas that fishing activities are heavy interference with fishing activities is inevitable and often ends up with valuable instrument lost The last three approaches utilize the principle of remote sensing and obtain data for interpreting wave conditions A remote sens
66. l Distortion Since the detected radar signal strength S is inverse proportional to the distance from a subject to the radar antenna r according to S f r the recorded signals for the entire radar observation domain will be different even the sea severity is the same for the entire domain For example the signal strength varies significantly from 0 to 1000 for the raw image Fig 5 1a The numbers mentioned here are integers recorded from the high speed ADC There is no need to transfer these integer numbers to floating numbers for voltage because these numbers does not represent true wave heights anyway Nevertheless the range of these numbers represents a significant range Since the attenuation of radar signal strength is proportion to r an intuitive approach to reduce the signal difference would be taking an one third power on the signal This will reduce the signal difference caused by distance significantly For example Fig 5 1b has a much small 52 range from 0 to 11 Notice that there is no theoretical proof yet for this approach and a relative difference still exists in the signal Nevertheless the signal difference caused by distance does reduce significantly This process seems not having a great effect on the naked eyes if the wave period is short with a short wavelength but it can be better seen when the wave period is large on Feb 18 2004 08 00 Fig 5 2 1200 021704418 2000 800 E gt i00
67. mon pin for power and standby switch Fig 3 2 Wiring diagram for turning on and off of a FURUNO 8251 radar 3 2 Batch File for Controlling the PC programs After the PC was turned on the Windows 2000 operation system will be loaded automatically first After this a batch program radar bat will be launched automatically by leaving this program in the Startup sub folder which is under the folder of C Documents and Settings Start Menu administrator This batch program contains the following five commends c radar debug killtime exe c radar debug radar exe Move rd h d data Move rd b d data c autologon shutdoen qsd s 21 The first commend executes a program killtime to let the PC idle for 100 seconds This idle is for letting the rotating speed of radar antenna approaches a steady condition The second command executes the radar image data acquisition The results of this acquisition are two files RDmmddyy hhr and RDmmddyy bhr where RD in the filename stands for radar mm dd and yy will be replaced by the integer number of the month day and year when the data was acquired The first h in the file type stands for an ASCII header file and the hr will be replaced by the integer number of the hour when the file was created The first character b in the file type stands for a binary image data file For example RD0O11204 h01 and RDO112
68. mpleted yet and 2 the transfer speed limitation on USB 2 has not be checked for radar application Nevertheless this may be a future option when the power consumption is a major concern 2 6 Selection of ADC Rate Is it necessary to use the maximum ADC rate when digitizing a burst line image Also is it necessary to digitize every burst line images These two questions are important and the answers also determine the image size Resolution in Angular Direction The 1750 burst lines for a half circle mean a resolution of 0 1 degrees 180 degrees 1750 scan lines Since the antenna takes 0 833 seconds for a half circle the time between each scanning line will be 0 833 s 1750 0 476 ms The swept distance at 5 km away would be 5000 m 0 476x10 s 0 6 rps 2 n 8 97 m That is to say at 5 km away the ADC digitized spatial resolution is about 9 m Notice 16 that this number is much smaller than the horizontal angular spreading 78 m at 5 km away from radar When close to the radar both the ADC resolution and spreading resolution increase because of the small radius distance but the ratio remains the same 78 9 8 6 This implies that there is no need to digitize every burst line images If selecting to digitize one line image for every 4 lines it would be still good enough because of the ratio is still much less than 8 6 For this reason we carried out a test at the early stage to compare the image quality for two options 1
69. n ae ats a E EA 74 G22 Data AMalysi epopee E ad ieee ieee dreamed eres es 11 6 3 Measurement Results ssssssseserrrrssesesssrerrreereerrreesrrrrerreesen ae 6 4 Wave Data from CHLV2 and VAOOL occ cece cence ene en ees 84 6 5 5ipnal Noise Ratio SNR aoaea E ete ao E E 87 6 6 Resulis er E sales a n vite ha Adds aaa gies E E E TEST IATa 89 ii Chapter 7 Remote ACCESS acs vets acet sed ch nesa cites ra cits on ade eee eens dey dese ase 92 7 1 General Requirements 7 2 Remote Control and Access by LAN 7 3 Remote Access by Modem as sccacesedsvaaiwiesueiedi Aue daddee eres otek 95 7 4 Software for Remote Control 2 0 0 0 0 0 c ccc ccc cc cece ence cece eeeeeeee sees 96 Chapter 8 Discussion and Conclusions cccceece cence ence eens eeaeeeeeenaeenas 98 8 1 Improvements on Hardware 52 ss 0nscss Ase sreupessosnes Muveshenneaeeebeseaes 98 8 2 Limitations eare a cece cece cece cece ence cece DATT E E E 101 9 97 Other Features ahere ees disadesas cobs bieulie a e peidus canebiteads sated 103 8 4 A Tool to Verify Numerical Model Results cc cece cece eee eee 104 5 CONCIUSIONSS lt ccs eee ares Foss case cehs Sean ace eee g deca OTTER 104 References ss cess hehe tee hdd uae tees Sede a dd chtes fase Suid Lass Sods hws weenie whe OSa 106 Appendix I A BASIC program runs in the TFX 11 for controlling the PC and the radar In attached CD only Appendix II C program codes for acquiring radar images
70. nd T Asai 1993 Modification of the extended maximum entropy principle for estimating directional spectrum in incident and reflected wave field Report of P H R I 32 4 25 47 Johnson D 2005 Directional WAve SPectra DIWASP Toolbox for Matlab Centre for Water Research University of Western Australia 35 Stirling Highway Crawley Perth WA 6009 Also available on http www2 cwr uwa edu au johnson diwasp diwasp html 106 Kobayashi T A Kawai M Koduka and T Yasuda 2001 Application of nautical radar to the field observation of waves and currents In Ocean Wave Measurement and Analysis Edge B L and J M Hemsley eds ASCE Reston VA USA Krogstad H E J Wolf S P Thompson and L R Wyatt 1999 Methods for intercomparison of wave measurements Coastal Engineering 37 235 257 Lee J H S Takewaka T Sakai and S Takano 2005 Use of X band radar for wave and beach morphology analysis Proceedings of the International Conference on Coastal Engineering World Scientific Publishing 3 2681 2693 Leu L G 1998 Spectrum Analysis of Ocean Surface Wave and Coastal Water Depth Derived from Satellite Images Ph D dissertation National Chiao Tung University Hsinchu Taiwan in Chinese Oppenheim A V R W Schafer and J R Buck 1999 Discrete Time Signal Processing 2nd ed Prentice Hall Englewood Cliffs NJ Prandle D J C Hargreaves J P McManus A R Campbell K Duwe A Lane P Mahnke S Shimwell
71. ndwidth for the ADC card is necessary In general because the higher the ADC rate the higher the bandwidth of the ADC device and thus 100 MS s for the ADC card is specified The first ADC device has the longest history on the market and thus has more functions for applications but the product design is relatively old and thus consumes more energy 26 watts It was selected because it was the only high speed ADC card available at the time when this project started The second ADC device has a better resolution 14 bits a higher rate 130 MS s and less power consumption 9 watts but it is only available since early 2004 We have a chance to use this card for a similar project In general the function available for this card is limited for ADC only and thus cannot be used as an oscilloscope yet For 15 experienced users however this card would be recommended because of its superior ADC quality The third ADC device is available since middle 2004 but we have no chance to test it yet The above three ADC devices are all internal PCI cards and thus require a desktop PC to work with The fourth ADC device Handyscope 3 is an external USB 2 device and only available since early 2005 The advantages of this device are 1 it comes with a 14 bits signal generator and 2 it can work with a notebook for data acquisition and data analysis for less power consumption The disadvantages however are 1 the software support is not co
72. nector Int Modem Fig 7 3 The device connection diagram for WOM using external or internal modem 7 4 Software for Remote Control PcAnywhere from Symantec was selected for remote control between a host and a client This software provides a secure remote access for various types of connections LAN and modem Details of pcAnywhere commands can be found in the user s manual by Symantec This software has been checked in this project and there is no problem for transferring files folder and remote control by either LAN or modem Using a password furthermore the host computer can be protected from unauthorized access by unwanted persons In configuration by changing the option about access rights for each caller the access to the computer resource can be easily restricted 96 A feature of the most recent Windows XP Professional operation system has a built in function called Remote Desktop that is similar to peAnywhere This feature however has not been tested in this project yet For details see http www microsoft com windowsxp using mobility getstarted remoteintro mspx It is worth to point out that a broadband connection LAN would be the best but not necessary if only the measurement results such as directional spectrum and line spectrum are required to pass back to the data center 97 Chapter 8 Discussion and Conclusions The details of a X band radar wave observation system have been studie
73. neral this is not a concern because most of the current available PC has this capability For example the motherboard ASUS A7V8X used in this project has both options WOM and WOL When two computers that are connected by LAN or modem they are in a client host relationship The computer that controls the radar system is the host computer The host waits for the connection from a client a computer in the data center and provides the requested services A client connects to the host and instructs the host to carried out a specific job 7 2 Remote Control and Access by LAN It would be much simple and fast for remote access if a LAN is available A function called WOL over the internet connection would be used In order to use WOL 92 however the set up of BIOS on Power Management must enable the WOL and a fixed IP address and Subnet Mask address must be assigned for the host computer For these two addresses one has to consult the LAN administrator The operation principle of WOL is given next Even the host PC has been shut down but still connected to power the Network Interface Card NIC still gets power from a PC s ATX standby power supply A software burned in a chip on the NIC is constantly check for internet calls to its own Media Access Control MAC address If a repeated called of more than 16 times be detected the NIC will send a power on signal to the motherboard activating the power supply and booting the system
74. ng 100 degrees OF quadrant counted from positive x 60 384 Signal 1 level 5 600 984 3 2 E o 1 0 600 4 984 2 3 600 192 X m 192 Fig 5 7 First three rectangular radar images on 18 00 Feb 17 2004 for wave analysis With x y 3 m t 1 66667s domain size 384 x 384 m 61 150 100 50 0 50 100 150 Direction deg 80F b rd021704 h18 4 E m hz 8 20F 0 02 04 06 FREQ hz Fig 5 8 Results from radar images analysis on 18 00 Feb 17 2004 with x y 3 m t 1 66667s domain size 384 x 384 m a Directional spectrum b line spectrum The presented direction is for wave propagation direction direction With the selection of x axis orientation Fig 3 5 this direction can be translated as waves are coming from ENE 23 10 13 The line spectrum Fig 5 8b indicates a peak wave period of 5 3 s When using a grid size of 5 x 5 m the directional spectrum has a more concentrated energy contours Fig 5 9a and the line spectrum indicated a slightly different peak wave period 5 5 s Fig 5 9b When using the largest grid 1024 x 1024 m the 62 a rd021704 n18 S ee a ale fof beh heer Freq hz i i i i i i 150 100 50 0 50 100 150 Direction deg b rd021704 h18 E mhz 0 0 1 02 03 0 4 FREQ hz Fig 5 9 Results from radar images analysis on 18 00 Feb 17 2004 with x y 5 m
75. nt temperature may fall below zero or exceed 50 C then an industrial grade PC which has a operating temperature range from 30 C to 80 C is necessary For regular operation a monitor is not required But it would be nice to have one for checking the processes For this reason any monitor would be sufficient 2 4 Micro controller If power is not a concern of the radar wave observation system then there is no need to add a micro controller for saving energy In most application however power is a major concern because of the difficulty to get AC power supply at a remote site For this reason a micro controller Onset Model TFX 11 was added to the PC for turning on the PC the radar and turning off the radar for saving energy as well as extending the 13 useful life of the radar In general a micro controller with a real time clock three channels of digital outputs for switching the PC and the radar is the minimum requirement An Onset TFX 11 was selected because of its simplicity for program and minimum power requirements The TFX 11 micro controller requires 7 12 VDC 80 mA to operate at its full load and about 4 mA for standby conditions For this reason a small DC to DC converter that change the PC s 5V standby power to 12V was used to power the TFX 11 all the time Fig 2 5 A Basic program see Appendix J run in the TFX 11 was used to turn on the PC and the radar It was also used to turn down the radar The PC will
76. od for data analysis is limited to 3 D FFT Previous experience on wave data analysis on other types of wave measurement techniques suggested that a better approach might be possible For example the extended maximum entropy method Hashimoto et al 1993 showed a much better results for the wave buoy measurements The need of other data analysis techniques for radar images however has to be justified first because of the very different input data For example radar images have information from many different locations i e 128 x 128 points in spatial domain and 64 points in time domain The traditional wave data analysis techniques are heavily dependent on the information from time domain i e 4096 points but only have 3 points in the spatial domain with a total number of input data 12 288 points For this reason the techniques developed for the traditional wave measurement techniques may not be necessary superior than the 3 D FFT approach used in this study Actually the results presented in Chapter 4 demonstrated that 3 D FFT can produce very accurate directional distribution This is mainly contributed by the excess amount of input data 1 048 576 128 x 128 x 64 points for this technique The number of input data used for buoy data analysis on the other hand is only around 1 of the number of input data for radar image analysis 102 Another limitation on using this technique may happen if the bathymetry for the radar measur
77. omes out of the radar 23 The connectors that hook up the radar cable to the control and monitoring unit are the places to get these two kinds of signals Fig 3 3 Usually the echo signals are run in a coaxial cable because the weak signals require isolation from other signal lines and power lines that is bundled with others in the main cable that connects the two radar units It is relatively easy to find this line physically The exact pin number on the connector for trigger signals that send to the antenna unit can be found from the user manual provided by the radar manufacture For example the yellow and black lines in Fig 3 3 are for retrieving the trigger signals and ground for a Furuno 8251 marine radar Although there are 4 wires in this picture the other two wires are for the heading signals that are not needed for this application Only the yellow trigger and Black wire ground _ are used r Radar echo signal or Trigger pu Fig 3 3 Wires that soldered to the radar cable connector that goes to the radar control and monitoring unit for triggering signals The echo signal wire in a coaxial cable is also marked 24 3 4 C program for Radar Image Data Acquisition In a high speed ADC interface device there are usually two input channels for digitization Channel A or and Channel B one channel for external trigger source and one channel for auxiliary input The radar echo images are fed into one of the inp
78. oned potentials it is worth to point out that a small marine X band radar 6 kw could also be used for measuring waves with a limitation of a small range around 200 to 500 m from the radar The principle of this application is identical 103 to that of the radar used in this study and the only limitation is the range Because it is much easy to improve the antenna speed for small radars the accuracy of FFT can be improved This is particularly useful for offshore wave measurement where the bathymetry has little influence on waves 8 4 A Tool to Verify Numerical Model Results In our previous numerical studies on wave transformation near coast areas it is not uncommon to see a strong gradient of wave condition along the coast Because it is hard to deploy a sufficient number of traditional wave gauges for measurements it is hard to prove against the simulated results With the X band radar wave observation system however image analysis on different shore parallel sub domains are possible and thus can be used for the purpose of model verification Before the above mentioned application can be implemented however the question on different radar scatter reflections caused by different radar beam incident angles should be addressed first Because the radar wave signals are weaker if the incident beam is not normal to the wave crest lines Thus it is understood that the radar measured echo signals would be different even though the wav
79. or a distance of 5 km a total of 800 data points will be collected per burst line in the duration of 32 us for EM waves to travel 5 km and return back to the antenna This implies a data size of 1 6 KB 800 point x 2 byte point Notice that all the size mentioned in this report is in binary format not the ASCII format If the same data is saved in ASCII format it will take much more space and much longer time to read and write the same file For a half circle image with 437 burst line images one radar image will take 700 KB for storage Considering 64 radar images are suggested for data analysis one measurement will produce an image file with size about 45 MB In just one day the total size of acquired image files will be around 1 GB This is the nature that needs to be considered 2 7 Blind Zone When a radar antenna emitted signal it cannot be used to receive the echoes Depending on the model of radar there is a block out time for receiving the echoes Usually it may take about 100 to 200 ns to clear the residual and switched for receiving mode Thus a blind zone of 15 to 30 m 0 5 time delay 3x108 m s is possible Fortunately this can be easily measured with the radar Just look at the radar screen and turning a nob for cursor control will let you read the blind distance directly from the radar screen 18 Chapter 3 Data Acquisition With the understanding of hardware requirements details of the radar image data acquisi
80. ordinates because there should be few waves that travel in parallel with the shoreline an angle of 0 180 or and 360 degrees 43 Now the wave energy distribution is presented in k 9 plane Fig 4 9a and one more step may be useful to display the wave energy directional distribution by translating it into the most popular f O plane Fig 4 9b E Seer 2 EEE T eee eee aur rn PEE E EOE Rees Sa E e a e e i E E E TE Sees E EL PA PENE EO T A 150 100 50 0 50 100 150 0 3 2 fo ee ae aes a ae ag o i o L LE Oil ee a ete a a ose ida 150 100 50 0 50 100 150 Direction deg Fig 4 9 Directional spectrum obtained from analysis of the regular wave images T 10 s H 2 m direction 45 deg a k O spectrum b f O spectrum This translation follows the formula given by Young et al 1985 as dk 4 7 WSO if p k 6 4 7 where dk df is the Jacobian matrix between wand g According to the wave dispersion relationship in linear wave theory it can be calculated as 44 dk 47m4 gk tanh kh 4 8 df gtanh kh gkh sech kh Since line spectrum is quite frequently used in many applications it is also desirable to present the line spectrum as well This can be done simply by adding up the energy in all direction domains for each frequency band Fig 4 10 No matter what the coordinate system a wave energy distribution is presented the total energ
81. phic form 1 to plot the energy distribution for each frequency band or 2 to summary the results and plot the direction energy distribution in one figure In this section the results are presented in the first form only There should be at least 32 plots to present all the information However only those frequency bands that have a relatively large energy are presented in Figs 4 5 and 4 6 Because a series of snap shots are available the wave directional ambiguity problem was correctly addressed when the frequency is reasonably lower than the Nyquist frequency Oppenheim 1999 i e 1 2At Fig 4 5 When close to the Nyquist 37 frequency however wave ambiguity problem still remains Fig 4 6 This is because the time Fig 4 4 The first and the 30th images of a series of 64 artificial 2 D wave images n x y t generated with the conditions given in Section 4 1 3 38 a 0 096774 Hz E ratio 1 b 0 12903 Hz E ratio 0 369 k 1 m d 0 19355 Hz E ratio 0 409 AERAR Faa 0 1 0 2 0 2 0 1 0 1 0 2 k 1 m 0 2 0 1 Fig 4 5 Part of the calculated wave energy directional distribution using the time series of wave images given in the previous figure Direction ambiguity is gone with 3 D FFT when the frequency is far below the Nyquist frequency Only these frequencies that have a noticeable energy E ratio gt 0 2 are plotted 39 interval between two consecutive snap shots is too bi
82. r can be controlled for an angular domain that is facing the ocean Fig 2 4 This feature is helpful to 1 identify the time for starting image acquisition and 2 reduce the burst line number to 1750 for a half circle radar image In cases that the selected radar does not have this option of setting an angular domain for wave observation then the whole circle image will be examined For this 10 situation another signal pulse the radar heading pulse will be used to identify when the radar antenna is pointing toward a specified direction This heading pulse is also shown in Fig 2 4 but not used for this study SIGNALS v A Pulse for antenna gt heading direction One full circle 360 1 667 5 1750 Pulses to trigger Radar waves 0 1000 2000 3000 0 1 2 3 4 5 TIME millisec Fig 2 4 For a FURUNO FR8251 radar the radar scanning domain can be specified a Within this domain pulses are generated from the radar control unit at a rate of 2100 pulses s to trigger the burst of radar waves b Details pulses pattern within the scanning domain These pulses were also used to trigger the ADC conversion Depending on the selected maximum detecting range the duration or the number of sending EM waves in a burst is different This is because the larger the measurement distance the more the EM waves are needed to produce enough echo strength for the antenna to pickup More
83. r to use WOM One modem dials and connects to the other modem Similar to WOL WOM is a function to wakeup the computer from the power off mode by receiving a phone call However this operation requires that the host computer be properly powered off see next paragraph Figure 7 3 explains the device connection for WOM with an external or internal modem Both types can be used for WOM but an external modem will need another power supply in order to receive the call In this study an external modem from US Robotics Model Sportster was tested and proved that it could be used to perform the WOM Notice that a wireless modem is just functional like an external modem The only difference is the service provided by the phone company In future it is evident that a wireless connection via Personal Communication System PCS would provide a more convenient access For the motherboard ASUS A7V8X used in this project WOM works only under the soft off mode that can be made by pressing the power off switch for about 4 seconds This soft off requirement however may vary among motherboard venders One needs to check the user manual or to consult with the motherboard vender for this kind of setting 95 Despite of the relatively slow communication speed the modem to modem connection does not have the problem to across a security firewall To Tel Line COM Port Ext Modem From Tel Line To Telephone WOM Con
84. s b Details pulses pattern within the scanning domain These pulses were also used to trigger the ADC conversion 11 Fig 2 5 Scheme diagram of the PC and radar auto control cece eee ee eee es 14 Fig 3 1 System diagram for the radar wave observation system The dotted boxes mark the hardware installed and the dashed lines mark the flow of control signals and radar image of the system All the solid boxes are from the radar manufacturer 20 Fig 3 2 Wiring diagram for turning on and off of a FURUNO 8251 radar 21 Fig 3 3 Wires that soldered to the radar cable connector that goes to the radar control and monitoring unit for triggering signals The echo signal wire in a coaxial Cable is also MAtked cicwhsnesisssuecedesras a E a tease peeaiu E ER E GE 24 Fig 3 4 A sketch to show the algorithm for finding the first trigger pulse P1 when the data acquisition software starts This algorithm requires a radar has the capability of setting an angular sector for observation Between time t and tz there is no trigger Fig 3 6 An example of the radar images obtained at the Virginia Beach on 18 00 Feb 17 2004 a All the radar burst lines 1750 are used for image plot b only 437 burst lines are used for the IMAGES ois cieccss ceverde svete seeehas want ae deeoua deegareescens 29 Fig 3 7 Sketch to show the image distortion caused by side or side lobe effect when there is a strong ec
85. s off from the direction that waves are coming from 80 m s deg 0 035 J 0 03 300 feb 3 E 0 02 270 90 T 8 OO 0 01 Cc 8 240 Wee a 120 180 2 5 T t T T 2 Line spectrum with Hs 1 32 0 0 1 0 2 0 3 0 4 0 5 Frequency Hz Fig 6 6 Wave condition on 1 00 March 18 2005 a Directional spectrum b line spectrum The directional spectrum on 1 00 March 18 2005 showed three major wave groups Fig 6 6 The largest wave group with a dominant frequency about 0 175 Hz came from NE direction and the two minor wave groups with dominant frequencies of 0 1 Hz and 0 27 Hz came from E and NNE This phenomenon may represent a developing sea with a very dynamic wind field because the wave periods for all the three groups were not large enough This phenomenon was also seen on the wide line spectrum Fig 6 6b 81 The directional wave spectrum at another time 16 00 March 23 2005 Fig 6 7 showed a complete different sea condition There was only one long period dominant wave component which represented a nearly perfect swell indicated by the narrow band line spectrum On 10 00 March 28 2005 the sea condition represented another developing sea This time however the change in wind speed and direction are probably limited Waves were mainly coming from E direction and have a quite large directional spreading Fig 6 8 m s deg 0 12 gt 01 3 Cc o 0 08 E O
86. st period during the wave measurement period 11 00 March 16 22 00 April 6 2005 This data may represent the change of tidal elevation At two points unfortunately data were missing due to a bad sector on the Compact Flash memory 11 Elevation m co z o 7 i i i i 03 14 03 19 03 24 03 29 04 03 04 08 Date 2005 Fig 6 3 Time averaged water surface elevation during the period of measurements This indicates a mean water depth of 8 2 m The wave analytical results significant wave height Hs period of peak wave energy Tp and the direction of the peak wave period Dp Dominant wave direction Da from the star wave gauge records are shown in Fig 6 4 In this study significant wave height was calculated as 4 times the zero th moment of the line spectrum e g Fig 6 6b Peak period corresponds to the highest point in the line spectrum Direction of peak period is the main direction of the peak period Dominant direction is defined as the direction with the highest energy integrated over all frequencies During the measurement period H varied from 0 24 to 1 44 m with a mean of 0 68 m The highest Hs was found on 10 00 March 28 During the measuring period there were four time spans when H were greater than m see the arrows in Fig 6 4a and Table 6 1 T was within the range of 3 2 16 7 s with a mean of 9 3 sec Relatively longer period waves occurred with a period of 12 5 16 7 sec at 16 00 March 21 00
87. te Virginia Beach VA Because of the relatively large radar wave spreading 25 degrees in the vertical direction and the selected radar elevation a strong reflective subject at a distance that is close to the radar will be seen as a subject that is further away For example the bright yellow lines near the bottom center in Fig 3 6 were caused by the strong reflection of white foams on the breaking wave crests This line should be a straight line because the shoreline is straight at this site but it was shown as a curve in the image This radar image distortion can be explained in Fig 3 7 as the side lobe effect The strength of echo 28 signal at the short distances Lp caused by the side EM waves exceeds the signal strength that come back from the distances L that the travel times for the EM waves really represented If there is no side lobe effect then the breaking foams near the radar center will not be seen If the height of radar antenna is low enough or the subject is far enough from the radar antenna then the distortion will be negligible Actually Fig 3 6 indicates that a distance about 500 m is needed to have a negligible image distortion 2500 1200 E 1500 Pa L 200 T e O w 400 500 500 as 1500 2500 Ruddy inlet breaking Distance x m i 2500 E Nr Py L 1500 T m A 500 0 i 2500 1500 500 500 1500 2500 Distance x m Fig 3 6 An example of the radar images obtained at the Virg
88. the hardware cost increases sharply for the large power radar As a practical application for a radius of 2 to 5 km a 25 kw X band radar is necessary This translates to a radar cost of 8 000 12 000 cost in 2004 depending on the manufacture and other options By specifying a monochromic monitor for the radar the total cost of a 25 kw X band radar may be below 10k For example a Furuno 8251 marine X band radar meets all the above stated requirements and thus selected for this project The selection of a radar antenna may affect the resolution of radar image Because of the entire radar system is a commercial product the antenna available for a particular radar model is usually limited or fixed For example for a Furuno 8251 radar one may select a 6 ft or 8 ft long antenna The antenna rotation speed is also limited to 24 or 36 rpm for a Furuno 8251 marine radar In general the longer the antenna the higher the spatial resolution of radar image in the radial direction Also the faster the antenna rotating speed the higher the temporal resolution of analyzed results in time domain For this reason an 8 ft long open array antenna that rotates at 36 rpm was selected Fig 2 1 8 ft ve antenna lt antenna base Tie down3 lt Cable to radar monitor Fig 2 1 Setup of a X band radar at a building roof Another advantage of a Furuno 8251 marine radar is that a sector of radar detecting area can be specified For e
89. then starts to wait for the next 1 pulse at time t4 25 One full circle 360 1 6678 on 1750 Pulses to trigger Radar waves SIGNALS v TIME not on scale Fig 3 4 A sketch to show the algorithm for finding the first trigger pulse P when the data acquisition software starts This algorithm requires a radar has the capability of setting an angular sector for observation Between time t and to there is no trigger signal The above paragraph ensures that the program always starts to do ADC from the first trigger event which also represents to start ADC at the beginning of the selected observation domain After this time a selected number of antenna revolutions e g 10 turns is skipped During this period the radar images are not digitized only the number of antenna revolution is counted The purpose of this process is to give a little more time for the antenna rotation to reach a steady condition 26 The final step is to digitize radar image on the selected burst line images It is mentioned in Chapter 2 that not all the 1750 burst line images are required to be digitized This study indicates that to digitize one burst line and then skip the next three burst lines would have sufficient image resolution and that is how the C program was coded The documentation of the above algorithm should be sufficient for readers to follow the C program codes which is given in Appendix II The rad
90. ther is an ERDC station VAO01 located offshore from the Rudee inlet at a water depth about 8 m The location of Sta VAOO1 is right beside the radar station and thus would be valuable for calibration Unfortunately 84 Station VA001 only has continuous operation from 1992 to 1997 and completely stops for operation after 2001 Although the wave record at Sta CHLV2 is not comprehensive neither but it has wave records for most of the year 2004 Nevertheless a period of time in 1996 and 1997 that both stations have wave measurements and thus a correlation of wave heights at these two stations can be conducted The results Fig 6 10 indicate that the significant wave heights Hs at Sta CHLV2 can be converted to the Hs at Sta VAOO1 for calibrating the radar measured SNR to Hs Thus there are extra data Fig 6 11 for the calibration purposes 4 T T T T f T P L H VA 0 7 H _cuv2 y 4 a H m at CHLV2 Las a 1996 February March April May and November Fa 4 L 05 1 2 3 4 T T T T T F S f 1 at af T 3H 4 4 abies a pa F a8 A 4 8 pi 2 F fou 4 H ya 9 7 H curva 1 J L b 1996 December 1997 January March and April 0 a L L 1 1 4 0 1 2 3 H m at VA001 Fig 6 10 Relationship between the significant wave heights at Stas CHLV2 and VAOO1 85 a CHLV2 2004 Feb 17 21 0 00 TIME day on March TIME day of Aprl Fig 6 11 Re
91. tion are presented in this chapter 3 1 System Control The information presented in this section is for the automatic radar system control Fig 3 1 All the added hardware is placed inside the PC The main control unit is a micro controller TFX 11 from the Onset Computer The functions of this micro controller are 1 turn on the radar at 56 minutes of each hour to warm up the radar 2 turn on the PC at 58 minutes of each hour to prepare for data acquisition 3 turn on radar operation at 59 minutes of each hour and 4 turn off the radar when the job is done at 8 minutes of each hour The schematic of this control is given in Chapter 2 and here the control software and other details are presented A BASIC program Appendix I sets a digital I O port high to turn on a NEC PS2506 optoisolator for activating a Nais TF2 12v Telcom relay Fig 3 2 This relay will close the circuit and provide a pulse to activate one of the first three functions mentioned in the previous paragraph For turning off the radar two digital I O ports are required to set high In general the above settings are universal for all kinds of radar and PC The only two concerns are the capability of a relay to handle the electrical current and thus the total power required for the task For example the selected miniature relay i e Nais TF2 12v Telcom relay and the miniature 80 mA DC to DC conversion unit change 5 V to 12 V are sufficient for the selected Furuno 8251
92. ut channel for digitization e g Chan A and the radar trigger signals are fed into the channel for external trigger source Because the capability of selecting a high input impedance e g 1 MQ for both of the channels the hookup and splitting of these two signals will not affect the original signal strength In the C programming the first task is to find the first trigger pulse that representing time tz in Fig 3 4 In this figure t and tz represent the end times of two consecutive antenna revolutions and tz with the first pulse P1 represents the start of radar image scanning Because the time to start the C program is not necessary between time t and tz the first detected pulse has a quite good chance to fall between tz and t3 For this reason the first task is to count how many trigger events have been received from the external trigger source Since the time interval between each pulse is 475 us if there is no trigger event after a sufficiently long time for example 1000 us then it is clear that the program has come to a time that is after t3 So the program just starts waiting for the next 1 pulse that represents at time t4 If the program successfully counted up to 1747 pulses slightly less than the ideal 1750 pulses with a time interval less than 1000 us between each pulse this also means the program has come to a time that is close to t3 With this situation the program just waits a few thousand microseconds more and
93. ut 0 03 m but at the lowest frequency band i e for f 0 00937 hz was used as the noise Following the work of Alpers and Hasselmann 1982 the suggested relationship between Hg and SNR was given as Borge et al 1999 H A Bv SNR 6 2 where A and B are two calibration constants Results of the effort to find A and B are given next 6 6 Results The first definition of SNR Young et al 1985 however does not show any correlation between H and SNR Fig 6 14 The reason of this phenomenon is not clear at this time yet It is possible that the definition of SNR given by Young et al 1985 may just be a parameter to judge the quality of radar image and cannot be used to convert to Hs More studies are needed to further address this issue According to the second definition on the other hand the relationship is quite clear Fig 6 15 Although the data are somewhat scatter but the trend is clear Coefficients of the regression equation are also marked in the figure 89 T T T T T T T 0 2 F 0 084375 Hz F 0 14062 Hz 0 2 0 2 k 1 m 0 1 0 2 Fig 6 13 Examples to show a fraction of the dispersion shell with energy within that frequency band for radar wave image measured on 10 00 Feb 19 2004 Despite the effort to conduct ground truth measurements on wave height the radar measurements after December 2004 are not good because of the interference on
94. was calculated as 2n gT The size of the computed wave field had 128 x 64 points with a spatial resolution of 10 m in both the x and y directions in other words 1280 and 640 m in the x and y directions respectively For waves in an intermediate water depth and if the water depth h is known then the wave number can also be obtained using the linear dispersion equation o gk tanh kh where o 27 T 34 o 200 400 B00 S500 1000 1200 X m Fig 4 2 An artificial 2 D wave image n x y generated from an equation with 5 monochromatic waves with period 4 5 7 8 and 10 s The wave amplitudes are the same but the wave angles 160 100 60 65 and 0 degrees and phases are different The results of calling FFT2 with FFTSHIFT are given in Fig 4 3 Because there is only one snap shot of the wave field the wave direction cannot be addressed and thus the problem of direction ambiguity remains Nevertheless for the given wave condition the FFT2 results clearly show all the 5 wave components The magnitude for each wave components however cannot be equal because of the requirement for the best spatial resolution is different for each frequency Figure 4 3 can also be translated into energy distribution in frequency f and direction 0 This task however is carried out later in Sec 4 2 35 90 0 3 0 2 0 1 0 0 1 0 2 0 3 k m Fig 4 3 Calculated wave directional distribution using the wave image
95. widely available on the market For this reason the cost for hardware is reasonable and the use of x band radars for wave observation if the details are fully documented would be a promising alternative The first attempt of using X band radars for wave observation was reported by Young et al 1985 At that time radar images were recorded on papers and then digitized for wave data analysis Since that attempt continuous effort on the development of X band radar wave observation system has produced several commercial products with specially designed hardware For example WaMos II Borge et al 1998 1999 Borge and Soares 2000 Krogstad et al 1999 Wyatt et al 1999 Wolf and Bell 2001 Wyatt et al 2003 was developed by following exactly the same principles given by Young et al 1985 The other type of X band radar wave observation system is Miros wave and current radar http www miros no Miros has no rotating radar antenna and it is only good for a short range lt 450 m observation of waves The problem associated with these commercial products are 1 the price is relatively high about 4 to 5 times of the hardware cost and 2 source codes for data analysis and system control are not provided This means the operation is somewhat like a black box operation Thus it is not good for the academic research purposes For this reason a study of the entire processes of using X band radars was proposed for revealing the details
96. xample when using a radar at a coastal station only the half circle image that facing the ocean is useful With this capability although the radar antenna still rotates at the constant speed as usual but only sends out radio waves for the half circle that is facing the ocean This capability avoids the unnecessary exposure of radar operators or any creatures on the landside even out of the harmful zone that is about 5 meters from the radar More details on how to uses this feature is given later in this chapter The installation height of the radar for wave observation is another critical factor There is a better range for picking up the scatter wave signals This range depends on the radar wave incident angle Fig 2 2 The EM waves that come out of the antenna usually weet Horizontal ae P Fo ee a o D a aa te i Maximum EM n Xa wave energy antenna EN breton i Little contrast L Better working area L i Little scatter waves return to Antenna Fig 2 2 The better working area Ly of a radar wave observation system have a vertical spreading angle of 25 At least half of the EM waves are wasted because they are going above the horizon Only the radio waves with an incident angle between 1 and 10 from the lower half of the radio waves are useful For this reason the installation height and the radar output power are the two main factors that control the range of wave observation A simple relationship betw
97. y plane to show the directional spreading at a frequency band close to the given peak energy frequency for the random sea generated by using DIWASP ae a Analyzed 7 a eae aaa kane aa oer hal 0 2 0 1 No 03 g s2 0 2 0 1 150 100 50 0 50 100 150 Direction deg Fig 4 14 Comparison of directional wave spectra a Analyzed from the random sea images generated by using DIWASP b the given input spectrum 50 Given regular wave conditions T 10 s H 2 83 m Given spectrum hS A Analyzed spectrum 1 l 0 0 1 0 2 0 3 FREQ hz Fig 4 15 Comparison of the analyzed line spectrum for the given random waves images 51 Chapter 5 Data Process for Radar Images The data analysis tool presented in the previous chapter uses data generated on a horizontal plane without any distortion Radar images however are obtained from side view with distortion For this reason there are a few steps that need to be done before wave analysis can proceed These steps are 1 reducing the signal distortion caused by different distance 2 judging the sea severity 3 selecting a small rectangular sub domain 4 interpreting signals for the sub domain and 4 analyzing the wave directional spectrum Following the material presented in this chapter one should have no difficulty to understand the computer codes in Matlab for data analysis that is given in Appendix III 5 1 Minimize Signa
98. y should remain the same This can be checked by using the total volume vo under a directional spectrum or the total area mo under a line spectrum This is because the significant wave height H can be found as H 4 02 m 4 02 v 4 9 Notice however the H calculated in Eq 4 9 is based on the random sea with a Rayleigh distribution on wave height for unit sea surface area Dean and Dalrymple 1992 In other words the effect of computing domain should be excluded For monochromatic waves the input wave height specified is actually the root mean square wave height H ms that is H 1 414 For example the given input monochromatic wave height is 2 m that is corresponding to specify a H of 2 83 m The calculated H during various stages of the Matlab program FFT3D_RADAR M see appendix III are around 2 84 m This example indicates a small error of 0 01 m for the selected settings on Ax Ay At and simulation domain This represents an error around 0 4 For other tested wave periods with the same wave image domain 896 m 128 7 m image resolution 7 m x 7 m temporal domain 53 s 32 1 66667 s and temporal resolution 1 66667 s the results are given in Table 4 1 In general the result 45 is good except for the short period waves i e the 5 s wave trains The average error is about 8 in terms of the calculated Hg if the case for 5 s waves is excluded 250 200 150 100 Wave spectrum m hz

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