HDSS Manual - Ocean Physics Group
Contents
1. 7 Set SonarDas monitor app to the current data directory a click the Choose Directory button and navigate to the current RAW data directory i e HDSS 50k Data Copv1 50kHz KNOX18RR RAW The application will start plotting the latest sonar data from that directory in the Sonar Playback Window The recorded TDS data are displayed in the TDS Graph Window b DO NOT PRESS THE Run TDS OR Run Sonar BUTTON ON THE SONAR DAS WINDOW These controls are deprecated and have been removed in the latest release 8 To stop either sonar type lt q gt and press lt enter gt key from their respective Terminal shells To re start the sonar press the lt key up gt from the Terminal to select the last command lt path gt SonarAcq and press lt enter gt key to restart If the sonar fails to quit and is still pinging manually stop the sonar controller as instructed below If the HDSS does not start 1 Verify that TDS program is running If not stop the SonarTDS and SonarAcq programs type lt q gt and press lt enter gt key from their respective shells 2 1f TDS is working stop the SonarAcq program by typing a lt q gt lt ret gt reset the OPG Doppler Sonar Interface Unit and restart the SonarAcq program Manually stopping the Sonar Controller 1 Double Click the application GoSerial or CoolTerm from the applications directory It should currently be set to the Sonar Controller serial port usbserial A700f4f7 and baudrat2. The planktonic communities are layered vertically Their horizontal variability is being mapped as the ship progresses The maximum range attainable by the 50 kHz is strongly dependent on the presence of a mid water scattering community that includes plankton squid and small fish This community is seen as a second maximum in sonar intensity between 300 600 m depth The diel vertical migration alternately provides enhanced scattering for the 140 kHz system at night and improved long range performance of the 50 kHz system during daylight The primary artifact present in HDSS data is a spurious apparent shear that in fact stems from rapid variation of scattering strength with depth This occurs only when the ship is moving and js seen only in the direction that the ship is going Beware of frontal like structures that migrate at dawn or sunset Comparing velocity and intensity displays provides insight The magnitude of this artifact is proportional to ship speed To quantify its presence slow the ship or change course IL INTRODUCTION The R V Revelle is equipped with a Hydrographic Doppler Sonar HDSS System which provides estimates of Absolute ocean velocity Ocean shear Acoustic scattering intensity e Scattering intensity gradient plankton layering The system consists of two 4 beam Doppler sonars and assorted support sensors Figs 1 2 The Deep Sonar operates at 44 kHz and can profile to depths in excess o
3. lat 1x1440 double lon 1x1440 double Header data filename The basenames of sonar raw and covariance files whose data are contained in this sonar struct are stored in this cell array dasinfo HDSS specific setup variables are stored here organized in exact parallel to the binary C data structure TDS Time Domain Server contains all recorded environmental sensor data including GPS and VRU vertical reference unit Covariance data cov int etc Using the raw digital output of the sonar receivers a lagged autocovariance of the received signal is computed The result which contains Doppler phase shift information is averaged by range bin time gate and stored in cov A zero lag autocorrelation which represents the sonar backscatter intensity is stored in int The autocovariance procedure incorporates an matched filter which improves detection at the maximum ranges of the sonar This filter attempts to search near an expected phase shift caused by ship motions The IIR time filter used to center the matched filter can cause filtering errors due to a bottom hit or sudden ship motions to 17 persist over a period of several pings Therefore the unfiltered covariances and intensities indicated by a following O e g covO should be used when the ship is in shallow water or where ship s navigation data contain repeated spikes To allow for precise averaging across pings a motion correction algorithm is also applied to
4. HDSS interface 2 Sonar Electronics Taxi F O Taxi F O 140kHz System 50kHz System Controller Controller Receiver Transmit Receiver Transmit Tx Rx Accelerometer 1 Transducers Fig 3 Revelle Hydrographic Doppler Sonar Data Acquisition System 13 14 Fig 4 USB 8 com serial box for TDS Fig 5 RAID for HDSS 15 ACCESSING DATA Data from the Hydrographic Sonar System exist in three stages The first stage is Raw data which is simply the digital output of the digital basebanding sonar receivers This raw digital data is processed into Cov data files which contain single ping every 2 s covariance data which have been corrected for ship motions pitch roll yaw and averaged into range bins Covariance data are formed in real time and recorded in parallel with raw sonar data on the local sonar machines 50 kHz and 140 kHz CPUs Finally an automated process on the HDSS Server accesses the covariance data on the sonar machines copies the cov files across the network and forms finished products in Matlab format or mat files which include quantities of scientific interest water velocity shear scattering intensity as well as environmental sensor data GPS position ship attitude and engineering data sonar transmit receive and processing parameters electrical status It is expected that the Mat files will fulfill the immediate needs of most scientific users Nevertheless as improved p
5. removed if the disk becomes dangerously full HDSS Server The HDSS Server provides four main services 1 backup of covariance data 2 post processing of covariance into scientific quantities e g ocean velocity shear and backscatter intensity 3 near realtime displays of scientific data accessible over the ship s network on on a series of HDSS Server web pages and 4 user access to data both as covariance files and as post processed data in Matlab format Automated tasks behind these services are performed by a sequence of UNIX shell and Matlab scripts These are initiated at regular intervals lt 10 mins by an entry in the root user crontab A lockfile is created at the beginning of the cron job to prevent multiple executions of the possibly long Matlab processing stage If execution completes normally the lockfile is removed prior to exit A local mirror of single ping covariance data for each sonar 50 kHz and 140 kHz is maintained using rsync over ssh connections to each sonar acquisition machine The mirror is physically located on an external FireWire 800 drive labeled Server_EXT_xx which is secured in the back of the server rack All covariance files copied by rsync remain on the server even if they are removed from the acquisition machines by the FIFO mechanism Averaged covariance data are stored in Matlab files also on the external drive with one file per day At midnight each day a new file is created contai
6. the single ping covarince data The correction estimator is produced from the ship s VRU vertical reference unit inertial measurements This corrected data stored in covs and covs0 is the default version used in all subsequent velocity computations Velocities exist in three successive reference frames Beam coordinates beamvel ranges Positive inward Doppler velocity detected by each beam 1 Ai4 are computed from binned motion corrected covariance data covs and stored in beamvel The indices of sonar beamvel are bin x time x beam Ship coordinates u w u_z depths Velocities from the four sonar beams are combined into horizontal velocity u Re Im parts and vertical velocity w in the ship s frame of reference The ship frame is a right handed coordinate system Re u is pointed forward toward the bow Im u is across toward the port side and w is positive up Vertical shear du dz is placed in the field u_z Indices are bin x time Earth coordinates U w U_z depths Using the heading and navigation information from the ship s GPS units and Vertical Reference Unit VRU the horizonal ship frame velocities u are transformed to earth frame velocities U Re East Im North and vertical shear of horizontal velocity U_z Indices are bin x time Several useful fields are also included at the root level of sonar datenum yday lat lon datenum the TDS timestamp in matlab datenum format In multiple ping averag
7. R V REVELLE HYDROGRAPHIC DOPPLER SONAR SYSTEM USER MANUAL Ver 20 April 2011 Scripps Institution Of Oceanography Marine Physical Laboratory 8810 Shellback Ave La Jolla CA 02093 0226 tel 858 534 3863 fax 858 534 7871 http opg1 ucsd edu CONTACT NUMBERS Rob Pinkel rpinkel ucsd edu 858 534 2056 Michael Goldin mgoldin Qucsd edu 858 534 3863 Oliver Sun osun Wucsd edu 858 822 2580 Mai Bui mnbui ucsd edu 858 534 4733 TABLE OF CONTENTS I OVERVIEW To the Chief Scientist HDSS BACKGROUND HDSS OPERATIONAL CONCERNS Il INTRODUCTION SYSTEM OVERVIEW ACCESSING DATA Ill USER OPERATION For STS Personnel Only STARTING STOPPING THE HDSS SONAR DISPLAYS IV TECHNICAL REFERENCE HARDWARE DATA FLOW MATLAB PROCESSING TROUBLESHOOTING 22 26 28 29 I OVERVIEW To the Chief Scientist HDSS BACKGROUND The Hydrographic Doppler Sonar System HDSS on the R V Revelle provides profiles of absolute ocean current and acoustic scattering strength in support of scientific operations The HDSS consists of a 50 kHz sonar which profiles to depths of 700 1100 m and a 140 kHz system which profiles to 150 350 m The system was created to provide measurements with higher depth resolution than is available from commercial Doppler sonars Both the acoustic pulse length and the angular width of an acoustic beam affect depth resolution The HDSS sonars employ large transducers relative to the commercial system
8. anel immediately above The strong northward flows of the diurnal internal tide red fill the depth range of the high resolution 6m 140 kHz sonar The 50 kHz sonar can see the weaker currents below with 22 m vertical resolution Visiting science teams are welcome to use and keep HDSS data at the discretion of the Chief Scientist of each Revelle leg Operation of the HDSS is under the supervision of the SIO Shipboard Computer Group representative on board Requests to initiate or cease sonar transmission and or data recording should be addressed to this person The computer tech can provide hard copies of the HDSS data while at sea or at the end of each leg as well as guide the science team in the use and interpretation of the real time displays Following established UNOLS NSF practice the Chief Scientist can request proprietary use of the data for a period of two years following the cruise If not requested the data will be made publicly available immediately following the cruise In either event copies of the HDSS data are archived by the Ocean Physics Group at SIO who are available to assist with data processing concerns Meridional Shear Luzon Strait 0 025 100 E 3 s x 200 300 025 010 8 1 amp s s 010 0 010 E 300 si amp 600 S 900 173 5 174 174 5 175 1752 yearday 2010 IWISE 2010 Experiment prog L 2010 Figure 2 Meridional shear the derivative of velocity with depth from
9. cers are used for each Deep Sonar beam Each transducer is a mosaic of hexagonal sub elements Single transducers are used for both transmit and receive in the 140 kHz system In an effort to maximize reliability there are no active electronic elements in the underwater acoustic components residing in the transducer wells 2 Cables from all well mounted transducers and sensors are routed through stuffing tubes in the forward ends of the wells into the Revelle transducer void compartment between frames 55 and 52 3 The 140 kHz Sonar cables lead directly to a bulkhead mounted NMEA box that contains sonar electronics Fig 6 The Deep Sonar cables are lead upward one deck to a similar NMEA box mounted just below the Revelle s exercise room Fig 7 I doo 6 140 kHz The NMEA box in th Revelle s sonar void compartment ousing the 140 kHz Hi Res sonar electronics ie 7 50 kHz The NMEA box in the compartment below the Revelle s xercise room 23 4 Within each NMEA box are found sonar power supplies transmit power amplifiers T R switches 140 kHz only and tuning boxes receive pre amplifiers digitizers and an electro optical converter A sonar controller that generates the frequencies required for transmit and orchestrates system timing is also located in each box Signals from the center and the outer ring of the 50 kHz receivers are recorded separately Thus there are eight receive channels in the 50 kHz NMEA box vs fo
10. d start and a terminal output should indicate sensors being acquired Start the Sonar program by double clicking the Start Sonar icon on the desktop From the SonarDAS application select the Choose Directory button on the lower left Sonar Playback window Navigate to the current data directory and click the Open button The screen should now be updating realtime mode is selected by default 29 Checks before starting 50kHz and 140kHz Revelle Sonar applications 1 Check that all the cables are firmly connected 2 Check configuration Open default hdss_setup 3 Start the sonar by pressing the Start Sonar button 30
11. e 19200 2 After typing a few returns you should get a colon prompt 3 Type an lt h gt to halt the sonar controller The controller should now be stopped 4 Make sure the ammeter on the supply front panel is now stable indicating that sonar transmission has ceased SONAR DISPLAYS Data Plotting Options The SonarAcq program runs in terminal mode It only outputs diagnostic text with a small portion of the raw data each ping just before the transmit pulse is generated and the first and the last TDS packet spanning that ping The SonarDAS application can be run to plot a real time intensity of the ping as well as TDS data The program is automatically started after double clicking the Start Sonar icon It reads the data files specified by the Choose Directory button on the main window Selecting the directory of the current acquisition path i e HDSS_50k_Data_Copy1 50kHz_KNOX14RR should automatically plot the latest data acquired De selecting the Realtime Mode checkbox and using the sliders allows reviewing historical data I l 21 IV TECHNICAL REFERENCE A HARDWARE refer to figure 3 1 The transducers along with accelerometers thermometers and pressure sensors are located in two 12 x5 x4 wells in the ship s hull located just aft of frame 57 on the port and starboard sides of the ship Starboard facing beams are mounted in the starboard well etc Separate transmit and receive transdu
12. ecorded in binary format and stored on revolving buffers on the HDSS analysis computers Each sonar produces of order 1 TB month and the most recent 20 days are stored Raw data are useful for diagnosing system behavior or developing new processing methods They are NOT routinely transcribed or transferred off the ship The first level of processing is done in real time producing single ping profiles of echo intensity and a variety of echo covariance estimates all averaged into fixed depth bins corrected for the roll of the ship These Cov data files are reduced in size by a factor of 50 relative to the Raw data Month long records of Cov data are 20 30 G byte These files are available to the scientific party in near real time and are routinely archived Calibrated scientific products R V Revelle Hydrographic Doppler Sonar System jeam 1 Be am2 amp 50 kHz Deep Sonar 140 kHz Hi Resolution Sonar Beam4 Beam 3 Figure 1 A plan view of the Hydrographic Sonar beam orientation looking down from above are generated in a second level of Matlab based processing that is done at sea in near real time by a networked computer A variety of ocean velocity estimates are produced each using differing noise filtering criteria The Matlab output is typically averaged over 1 5 minute intervals user selectable Each sonar produces 1 2 GB month of minute averaged data The real time estimates of absolute velocity are vuln
13. ed sonar data timestamps represent the time of the first ping included in the average yday The decimal yearday which includes a integer day Jan 1 yday 1 anda decimal part of days since midnight lat lon nav Navigation data as recorded by the ship s GPS nav is the ship s velocity u iv in Earth coordinates 18 III USER OPERATION For STS Personnel Only STARTING STOPPING THE HDSS 1 Turn on the four Macintosh Mini Computers 2 Turn on Sonar Power Supplies and OPG Doppler Sonar Interface Units 3 Start The SonarTDS command line program a Check the setup TDS file double click on the file TDS_Setup on the TDS computer s destop Its format should be the same as the example in Appendix III b Double click on the Start TDS icon on the TDS computer s desktop c The Terminal application will start and run the SonarTDS executable in a terminal shell 4 The TDS will initialize serial ports for each sensor data stream from the and begin to run Verify that all sensors are reporting reasonable values and no Missing string xxx error message is displayed on the TDS screen 5 With the TDS running either sonar can be started up To do so 6 Start The SonarAcq command line program and SonarDAS monitor application a Check the setup Sonar file open the text file default hdss setup in the HDSS folder using the TextEdit app Its format should be the same as the examples in Appendices I II Change the run
14. erable to calibration shifts in the sonar and the various positional sensors It is common to post process the Cov files multiple times to adjust sensor calibrations SYSTEM OVERVIEW The major components of the Hydrographic Doppler Sonar System HDSS include Fig 3 1 The transducers located in port amp starboard wells recessed into the ship s hull 2 The sonar electronics mounted in NMEA boxes one for each sonar The 140 kHz is located in the Revelle s transducer compartment The 50 kHz is located below the exercise room 3 The HDSS interface unit one for each sonar 4 The Time Data Server TDS computer located in the ship s computer laboratory 5 The data acquistion and initial processing computers and displays one for each sonar 6 The advanced processing Matlab and display computer 7 Lab display screens actually igure 2 a The port sonar well viewed from below showing the 50kHz eep Sonar grey hexagonal array and 140 kHz High Res rectangular ransducers igure 2 b The starboard Sonar well showing beam 2 forward right and eam 3 aft left for both 50kHz grey hexagonal array and 140kHz rectangular 12 Ship subnet 10 16 50 xxx Astech G12 GPS Time 4 HDSS l USB Serial Astech ADU5 GPS Time PHINS VRU Pitch Roll HDSS B Data System i HDSS lu 50 kH RAID 50kHz lt _ USB Serial 3
15. f 1 km in favorable conditions Its depth resolution is approximately 22 m The High Resolution Sonar operates in a band near 140 kHz profiling with 6 meters resolution to depth of 150 350m depending on weather bio scattering conditions Both sonars are configured in the conventional 4 beam Janus geometry In plan the beams are oriented 45 relative to the fore aft axis of the ship s hull Figure 1 The depression angle of each beam relative to horizontal is 60 degrees The HDSS sonars transmit through a protective polyethelene window mounted flush with the ships s hull They are similar in principle to the commercial instruments found on many research vessels The HDSS sonar beam patterns are significantly narrower than those of most commercial systems The sonars transmit synchronously at 2 second intervals Coded acoustic pulses are used The sound scatters from plankton drifting in the water column From the Doppler shift of the return echo the relative speed between the ship and the water can be inferred GPS along with a variety of other support sensors is used to infer the absolute ocean velocity Precise calibration of the sonars and the various position sensors is critical to the extraction of ocean velocity With the ship moving at 12 kts a 196 error in the correction for ship speed corresponds to 0 06 m s a value comparable to typical currents in the thermocline The HDSS produces three classes of data Raw echo data are r
16. he most recent Raw data stored in revolving buffers 24 10 The fourth HDSS computer also located in the console has access to the data drives It reads the most recent Covariance data and forms time averages typically 1 min or 5 min of ocean velocity acoustic intensity and other quantities of scientific interest using Matlab scripts Data are displayed on the upper right screen in the HDSS Console 11 Raw data display screens Two flat screen displays in the Shipboard Computer Group display console in the Computer Lab present real time raw data from the HDSS sonars And These displays are primarily a diagnostic of the instantaneous operating state of the system 25 B DATA FLOW HDSS Data Acquistion Machines 50 kHz 140 kHz Raw interleaved output from the sonar A D converters are stored as RAW binary files on the external RAIDs which are connected to each acquisition machine and secured in the machine rack Bin averaged covariance data stored as COV binary files are written to disk in parallel with the corresponding RAW files A nominal size limit originally set as a convenient size which avoids filesystem limits is set for each file type The RAW and COV data files are maintained as a FIFO configuration the oldest files are automatically removed by a cron job once disk usage exceeds a preset limit Typically about 21 days of RAW data are kept on disk but the COV data which have a much higher removal threshold are only
17. ies for each sonar along with two Macintosh mini computers for data recording and preliminary processing Fig 9 The system is synchronized by a third computer Screen on upper right which runs the Time Data Server TDS program The Time Data Server orchestrates environmental data streams from the ships GPS the Ashteck ADU2 positional sensor a stand alone GPS G 12 timing signal the gyro compass the PHINNS ships orientation system sonar well temperature pressure and acceleration among others All operations are linked to a GPS time base provided by an Ashtech G12 receiver located on the ship s bridge Timing and all ancillary data are decoded and provided to the sonar operations programs by TDS The TDS program does not itself record this data 9 Data Processing The lower left computer in the HDSS Console receives and processes data from the 140 kHz sonar while the lower right computer handles the 50 kHz Deep Sonar Each runs a program called R V Revelle Sonar that receives digital sonar data from the NMEA electronics boxes and environmental data from the TDS The sonars are synchronized such that the short transmit from the 140kHz system occurs coincident with the final milliseconds of the Deep Sonar transmission In this way near range contamination of the 140 kHz signal is minimized Single ping 2 second averages of echo Covariance data are written on hard drives in the rack behind the analysis computers along with t
18. ils to start or hangs during operation Check Power Supplies The green lamp on the top of the NEMA box should be lit indicating power from rack supply is present You can also check the supply outputs inside the NEMA box The wires going into the fuse panel are color coded Yellow 5 V Blue 5V Green common Red 20V Brown 20V Grey common There are spare supplies and fuses located in the spares box in the forward electronics store room if you need to replace them A Power supplies are good but sonar controller fails to load after SonarACQ started 1 Quit sonar application and start the Zterm application 2 Set baud rate to 19200 by clicking baud button on lower left of control window 3 Set channel to KeySerial1 this corresponds to the 1 port of the Keyspan USB dongle 4 Type a few returns Each should be accompanied by prompt 5 1f you get a prompt type lower case L This should give you a list of setup parameters 6 If you receive no prompt the controller the USB serial dongle or serial cabling is malfunctioning Repeat serial and USB connectors Restart and repeat the test Time Data Server TDS To stop the TDS type lt q gt and press lt enter gt key in the TDS Terminal if the computer freezes press and hold the power button on the rear right side of the mac mini Re start the Computer Start the TDS program by double click the Start TDS icon on the desktop Acquisition shoul
19. name parameter to reflect the current leg name i e sonarRec runname 50kHz KNOXnnRR b Make sure that the Ammeter on the power supply is not fluctuating indicating that the system is still pinging If it is still cycling manually stop the unit before continuing see section Manually Stopping Sonar Controller below Note when pinging the 140kHz unit will show very small fluctuations only a few tenths of an amp The 50 kHz system has pronounced Ammeter fluctuations when transmitting c Press the reset button and wait for the ready indicator to light DO NOT PRESS THE RESET BUTTON IF THE SONAR CONTROLLER IS CYCLING If necessary manually stop the controller first d Double click on the Start Sonar icon on the 140 kHz and 50 kHz computer s desktop This activates an applescript that starts the SonarACQ command line program and the Sonar DAS application e Select the data directory for Sonar DAS f The Terminal application will start and run the SonarACQ executable in a terminal shell g The SonarAcq will initialize the system and begin to run Verify that the sonar and all sensors are reporting reasonable values Data are written to primary and secondary disk files with paths specified in the setup file default hdss setup These paths typically point to 2 external firewire drives mounted in the rear of the 50kHz rack The filenames are auto generated from the setup file with a date code appended see example below
20. ning a new sonaravg structure with a full timegrid datenum field but with all other data initialized to NaN As new covariance files become available through rsync the data fields in sonaravg are updated During each update velocity and shear are computed from averaged covariances and added to the sonaravg structure 26 The update process has a maximum lookback setting in days typically set at 3 5 Missing daily Matfiles within this limit are formed if covariance data are available Once sonaravg is brought up to date a set of Matlab routines create plots of beam velocities backscatter intensity per beam and zonal and meridional absolute velocity and vertical shear All plots are available on the HDSS Server website and are set to auto refresh once the page is loaded The default plot is a combination velocity shear plot in which the color scale indicates velocities and simple shading indicates vertical shears Plotting limits and scales as well as the time window covered by the plots are user configurable The number of pings per average is also user configurable in Matlab and is typically set to 2 or 4 minutes Longer averages are recommended during noisy sea states or low backscatter conditions however shorter averages are preferred if further processing e g explicit noise rejection or navigation correction is anticipated The current version of the plotting routines does not handle different averaging intervals within the plo
21. ost processing algorithms become available new Mat file products can be formed by reprocessing the Cov files Hence it is vital that covariance data are retained for future use Raw Data Format Binary file containing interleaved integer output directly from the sonar A D converters Also included in the file are a dasinfo header containing HDSS specific transmit receive and processing parameters and TDS time position and environmental sensor data corresponding to each ping sequence Covariance Data Format Binary file containing single ping bin averaged covariance and intensity data along with dasinfo and TDS data Mat file Data Format Matlab 6 data file containing a sonar structure of multiple ping averaged motion corrected covariance dasinfo and TDS data Further Matlab routines included by default add data products in scientific units velocites shears navigation sonar has the basic structure sonar filename 42x1 cell dasinfo 1x1 struct cov 170x1440x4 double int 170x1440x4 double 16 cov 170x1440x4 double int 170x1440x4 double covs 170x1440x4 double covs0 170x1440x4 double TDS 1x1 struct datenum 1x144 double sn 170x144 double nbins 170 ranges 170x1 double depths 170x1 double beamvel 170x1440x4 double u 170x1440 double w 170x1440 double u_z 170x1440 double nav 1x1440 double U 170x1440 double U z 170x1440 double yday 1x1440 double
22. s in an effort to minimize acoustic beam width A comparison of velocity Figure 1 and Shear Figure 2 data from the HDSS sonars and the Revelle s 75 kHz ADCP is presented below Just as ocean bathymetry is routinely collected from research vessels the HDSS has the parallel tasks of monitoring ocean currents and acoustic scattering wherever the Revelle sails while simultaneously supporting individual science missions The established policy is to have the system running and recording data at all times that the ship is underway unless restricted by political regulation or acoustic interference Following extensive tests it has been determined that operation of the HDSS does not interfere with simultaneous use of the Revelle s acoustic speed log 3 5 kHz sub bottom profiler Simrad 12 5 kHz swath mapping system or RDI 150 kHz and 75 kHz ADCPs Please do NOT turn off the transmitters on either HDSS sonar just to be sure without first contacting the Ocean Physics Group at Scripps ADD DATA ACCESS FROM THE DISPLAY CONSOLE KEYBOARD ETC Meridional Velocity Luzon Strait m s depth m 1 ms depth m depth m A S S p 173 5 174 174 5 yearday 2010 175 175 2 n IWISE 2010 Experiment prog L 2010 Figure 1 A forty hour record of Meridional velocity from the HDSS 140 kHz sonar top the 75 kHz ADCP middle and the HDSS 50 kHz sonar bottom The arrows in the lower panels indicate the field of view of the p
23. the data in Fig 1 The extremely fine gradients of velocity with depth are thought to be due to internal waves fronts and small scale geostrophic features A global census of these motions The HDSS can be programmed to operate in a variety of modes A nominal operation sequence is provided in which both sonars transmit at 2 second intervals phase locked to the Revelle GPS Single ping 2 second profiles are recorded The depth resolution is 6 m for the 140kHz sonar and 22 m for the 50 kHz sonar Modifications to this nominal format can be made but only with prior discussion and approval from the SIO Ocean Physics Group Please do not attempt to modify the operating sequence on your own I HDSS OPERATIONAL CONCERNS To measure absolute ocean currents of order 0 06 m s from a ship moving 6 m s the ships motion must be quantified to 1 Higher precision is desireable A host of instruments is interfaced to the HDSS to achieve this end A calibration shift in any of these sensors can eliminate the possibility of real time absolute current information Often errant sensors can be post calibrated using the ships navigation and the HDSS as references If real time absolute velocity knowledge is necessary it can be obtained simply by slowing down periodically and reducing the ratio of ship speed to ocean current speed JI he precision of the HDSS is limited by the motion of surface gravity waves These appear as a high frequency noise on
24. the subsurface signals of interest They also perturb the boat s trajectory by 1 m s rms in normal condition If each wave crest represents an independent sample of the wavefield unlikely the rms wave noise can be reduced to 0 1 m s by averaging over 100 wave periods requiring 20 minutes or more Efforts to remove the depth averaged velocity are partially effective in removing wave induced ship surging Sonar range is degraded by the presence of bubbles under the ship Bubbles are generated by breaking waves hull slamming and the ships bow thruster If sonar performance is a priority plan to transit slowly enough to avoid pounding Avoid use of the bow thruster The real time HDSS display presents depth time plots of velocity shear and scattering strength in the format of Figures 1 2 The display allows the option of removing a reference velocity calculated over some user specified level of no motion from the velocity estimates at all depths This greatly reduces the influence of navigational errors It is often an insightful and practical display The shear display presents the vertical derivative of velocity with depth This is relatively free of navigational uncertainty and provides a fine scale diagnostic of the motion fields being traversed Displays of echo intensity document the concentration of zooplankton the primary scattering targets for the HDSS Increases of shipboard or oceanic noise are also seen in this display
25. tting window if the ping averaging is changed old Mattiles created using the previous averaging interval should be removed from the Matfile directory New Matfiles will be backfilled to the lookback limit by the updater The hdssMatlab scripts from the HDSS Server are available for download and may be used with minor modification i e to point to local data or as templates for local data processing The most useful Matlab scripts are described in the following section 27 C MATLAB PROCESSING Creating Matlab files of velocity and shear from covariance data To create a single Matlab file from a collection of covariance data Place the covariance files in a separate directory and assign the following variables in your Matlab workspace gt gt sourceDir your directory path gt gt Navg pings to average 30 pings 2 s ping 6 s averages Run the following with the hdssMatlab directory in your path gt gt sonaravg AverageCovFiles sourceDir Navg This will return a sonaravg structure containing bin averaged motion corrected covariances and backscattering intensities along with header and TDS data To convert covariances to scientific units of velocity and shear do gt gt sonaravg ProcessCov sonaravg csound where csound is optional and specifies a local sound speed velocity ProcessCov may be re run on the same sonaravg at any time using a different csound if desired D TROUBLESHOOTING If System fa
26. ur for the 140 kHz system 5 Signals from the accelerometer temperature and pressure sensors in the transducer wells are digitized by an ADAM A D Module housed in the 140 kHz sonar NMEA box 6 The HDSS interface connects to the sonar electronics NEMA Boxes via a high speed point to point fiber optic data link using the TAXI protocol Data from the NEMA box is demultiplexed into a down converted doppler data stream and two auxiliary data RS232 serial streams The doppler data stream is formatted into ethernet TCPIP packets and sent to the data acquisition computers Fig 8 The serial data streams are split into individual RS323 jacks in the back The first connects the sonar controller located in the NEMA box to the the acquisition computer s serial to USB port The second connects the ADAM A D serial data output containing the accelerometer sonar well temperature and sonar well pressure to one of the TDS computer s serial to USB ports 7 The HDSS is operated from a Console located in the Revelle s computer laboratory Fig 8 by personnel from SIO Shipboard Computer Group From here AC and DC power and digital control instructions are provided to the sonars below through two Doppler Sonar Interface Units Digitized data are received from the sonars merged with data from supporting sensors and processed to provide real time estimates of velocity and scattering intensity 8 The HDSS Control Console consists of an independent power suppl
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