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LADAR Proximity Fuze - System Study -

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1. indexpeak peak CFD t pulse FWHM uses ceil_ range 0 CFD t pulse FWHM ceil_range displays a plot of the different signals INPUTS t vector time used to create the pulse pulse the laser pulse FWHM the FWHM of the pulse ceil_range an object in between the source and ceil_range will NOT be detected It is represented by the magenta cross on the plot u OUTPUTS o indexpeak peak index trigger time peak peak value maximum represented by the red cross on the plot Example requires crossing m FWHM 100 1 e 9 t 1 400 1 e 9 tau FWHM 3 5 pulse t tau 42 exp t tau 1 2 tau CFD t pulse FWHM See also crossing range Copyright 2006 2007 Eric Blanquer ericblanquer hotmail com Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Vo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Vo Yo Yo Vo sN Function global detect ldentify the temporal resolution delta t 2 t 1 Value of the time shift used to create the 2nd signal shift ceil FWHM 2 delta Set the ceil range to zero by default if nargin 3 ceil_range lt 0 1 ceil range eps end Derived the corresponding ceil time Figure C 1 CFD algorithm 1 3 67 if nargin ceil time ceil_ range 299792458 else ceil time ceil range 299792458 trigger_time1 2 end cei
2. 53 and y However the range dimension z represented by the color is lower while using a lower sampling frequency This phenomenon is represented by the apparition of larger areas with the same color in the 2nd picture 5 5 Zig Zag Scanning Figure 5 5 shows an example of Zig Zag scanning The parameters used to carry out the scanning are PRF 2000 Hz fs 100 Hz V 50 m s flight distance 3 m and FOV 3 deg The settings have been chosen so that no overlapping occurs Moreover this result shows the necessity of increasing the number of cells at the receiver in order to obtain a better image with more pixels m Absolute range error m Image to be scanned range image Scanned image range image lt MSE gt 0 917 amp m Figure 5 5 LADAR image using Zig Zag scanning Furthermore this LADAR image brings up the question of target recogni 5 6 CONCLUSION 45 tion using discontinuous images In Section 4 3 a primary target recognition method is described which implies the computation of MSEs In the Zig Zag scanning case the MSEs are computed on the whole images as before However two others extra MSEs are computed based on the processed pix els only It provides an alternative criteria for the target recognition using discontinuous images 5 6 Conclusion The simulations presented in this section give an overview of the possibilities of the simulator This is
3. 31 boing ag eg Bess 5 tow Cone one a f Target range je 7 555 a C dp tag conning j where CNC os a 1 p 4 o Pitt LADAR mage target rettectyty 01 j an wi Y SATTA TONS o 4 en ater ater 00m NS Ms ear pers a 00 0 05 1 15 2 25 3 35 4 45 si chidtion CAT ton Tire 4 d gt x10 toc Ms w V ms m 122 SCA z C Ps Pigi tarce a z D m x Detection soot z Mir este FOV deg 5 2e 5 oo v 200 na D OP TOMS cola m p 20 range meges 3 eg M0 2ime M Ley bortee bd ETETE Figuta 2 RUN 10 t Mie Cat Ves hesi To Dedtop Wiro Mb mi en image to be scanned range image Scarned mage range image e SON rn MEE gt 63 M a 4 9 b 8 61 50 A Ab un 8 zA A a me 7 e a Fe tg iai 4 gt Bb 2 gt a 1 et ee 4 x Pat Mila PE ye es mass 4 4 LA S 1 5 im Figure 4 1 Screenshot LADAR GUI l 32 CHAPTER 4 GRAPHICAL USER INTERFACE 4 1 Front Panel The front panel is the window located in the top half of the computer s screen after running the simulation file see figures 4 1 and 4 2 for details It consists of several types of elements which are best described here e axes axes enable the GUI to display graphics such as graphs and images e text static text boxes display lines of text Static text is typically used to label other controls provide directions to the user or indicate values e edit editable text fields enab
4. The descriptions are given as the following template GUI name parameter code name parameter type of the control o action and consequences Q Short description of the parameter units oe Here is the alphabetical list of the parameters altitude height edit atmospheric attenuation alpha edit B B edit ceil range ceil range edit Detection algorithm detect popupmenu divergence angle thetay fwhm edit f sc f sc edit Flight distance dim a edit FOV dim b edit Fs Fs edit FWHM FWHM edit looking angle looking angle edit nsa nsa edit PRF PRE edit Pulse power 10 edit Pulse shape shape num popupmenu receiver aperture r aperture edit SNR FACTOR edit SNR slider noise param2 slider System efficiency eta syst edit target reflectivity rho edit V V edit altitude height edit set height and displav the distance to the around heiaht is the Figure A 1 Help file 1 5 ov altitude of flight of the platform units m atmospheric attenuation alpha edit set alpha and display the atmospheric attenuation graph alpha is the atmospheric attenuation coefficient representing the attenuation due to the atmosphere with the expression exp 2 alpha R R being the distance from the source units XXX HP NN 00 oe B B edit set B and display the corresponding Bode diagram of the filter B is the bandwidth of the system from the receiver point
5. Time s Figure 2 5 Normalized laser pulses with 73 2 100 ns The second model more basic is called Gaussian pulse and comes from 9 It describes pulses with a temporal profile which has a Gaussian shape as follow p t exp sat x er 2 9 2 3 PROPAGATION ATMOSPHERIC EFFECTS 11 where T has the same meaning as in Equation 2 8 A realization of Equa tion 2 9 is shown in Figure 2 5 dashed line curve Note that p t is normalized to unity in the simulation as stated with Equa tion 2 2 in order to keep a constant total power independently of the pulse shape 2 3 Propagation Atmospheric Effects The atmospheric effects limit the performances of laser systems since the laser pulse travels through the air Many complex phenomena as turbulences beam broadening or intensity variations occur and perturb the laser beam If the reader is interested in finding more details about atmospheric propagation it can be found in 2 7 10 11 The weather is not a parameter that can be controlled and therefore is not part of the scope of this work Consequently the atmospheric effects in the LADAR simulation are reduced to the aerosol attenuation only The gases and particles in the air absorb and reflect the laser light This creates a loss modelled by Beer s law which represents the attenuation of the beam power with the travelled distance Assuming a constant atmospheric extinction coefficient the law reduces to a familiar
6. device development and to support system engineering studies The key attributes of this LADAR simulation are that i it is modular allowing great variations in design parameters such as pulse shapes power sampling frequency flight charac teristics or signal processing ii it works with arbitrary targets through the use of the appropriate 2D range image describing the scenery iii the models used are simple which give understandable parameters for the user 3 1 Discretization Lets start by recalling the description of the laser beam intensity U x y t of Equa tion 2 2 page 6 U x y t Io p t x I x y where x y and t take on discrete values This brings up the question of the resolution choices both in temporal and spatial domains Those resolutions have to be adapted to the characteristic dimensions geometrical and temporal in the simulation typically e a pulse has a width of 100 ns e a footprint has an area of 0 2 x 0 2 m for a target at 50 m The first consequence is that the temporal resolution has been fixed to 1 ns with respect to the pulse width The reason for this choice is that it gives a pulse described by one point every ns that is to say a discretization done at a frequency of 10 Hz As a consequence all the signal sampled at this frequency can be considered as continuous signals since the sampling done at the receiver stage uses a frequency x 10 108 Hz On the other hand the spatial resolution
7. one being scanned This can be interpreted as a primary target recognition method Part Il Results amp Reflections Chapter 5 Simulation Results The LADAR simulation has been developed to support system engineering studies To do so it produces simulated range images under a wide variety of conditions This simulator is of good help in understanding how the different phenomena affect the final images In this section some series of simulations are presented To facilitate the interpretations and to be easily understand able only one parameter at a time is changed The simulations illustrate the performances of the detection algorithms with the noise addition the rela tion between the footprint size and the resolution the sampling rate and its consequences on the range accuracy the Zig Zag scanning 5 1 Classical LADAR Image All the following paragraphs are based on the original LADAR image seen in Figure 5 1 It shows a classical LADAR image generation with default parameters m Ab Image to be scanned range image Scanned image range image nn m 9 61 7 60 m 6 59 u 58 E je a 5 57 5 4 al 2 j 3 E A 55 w wur 2 E 54 k F 1 Figure 5 1 Classical LADAR image Al 42 CHAPTER 5 SIMULATION RESULTS In this ideal case one may note that there is no noise added this is studied in Section 5 2 Moreover the sampling frequency at the receiver is hig
8. B is done by looking at the spectral content of the sent pulse which defines the required bandwidth B 2 6 LADAR Range Equation To conclude these previous sections about laser theory the LADAR range equation used in the LADAR simulation is derived and can be found in 5 It permits to compute the total optical power incident on the receiver element The LADAR using electromagnetic propagation the microwave radar range equation as found in 14 applies D x x T X Neyst 2 12 where P received signal power W P transmitter power W Q scattering steradian solid angle of source o effective target cross section m7 R target range m D receiver aperture diameter m To attenuation factor Nsyst System efficiency The effective target cross section is defined in 14 as 4 a A 2 13 Q where 16 CHAPTER 2 LASER BEAM PROPAGATION THEORY Q scattering steradian solid angle of target p target reflectance dA target area m For Lambertian targets diffuse targets Q tends to be replaced by the value associ ated with the standard scattering diffuse target having a solid angle of 7 steradians In the LADAR simulation the footprint is much smaller than the dimensions of the target Thus the target intercepts totally the laser beam and it is classified as an extended target In that case dA corresponds to the area illuminated by the laser beam on the targ
9. estimated to be able to simulate the noises Consequently in order to provide a 2 6 LADAR RANGE EQUATION 15 more schematic model a global factor handles the noise Indeed if all these noises are unknown it is known that their combination yields a Gaussian distribution Moreover the standard deviation of this Gaussian distribution has the value of the Noise Equivalent Power NEP Since the power of the sent pulse is known it is possible to modify the Signal to Noise Ratio of the received signal In the LADAR simulation the SNR can be modified and then reproduce different noise levels An important parameter for minimizing the noise at the receiver is the band width B of the electronics following the optical receiver With a too large band width too much noise is admitted in the system With a too narrow bandwidth parts of the received signal are modified or suppressed To increase the SNR a com promise has to be found between accepting noise and modifying the received signal The shape of the sent pulse is known so this implies that its frequency contents are also known Under the assumption that the received signal is not too distorted during its travels and during the reflection one can consider that the sent pulse and the received pulse are similar in time and frequency domains This assumption is realistic for a long pulse which is the case in the LADAR simulation since the pulse width lies around 100 ns Then the compromise on
10. in the range images that is to say the distance from the laser source They also ought to contain the surface characteristics slope material in each pixel Another point might be the implementation of a dynamic range image generation This would permit to work with the exact view of the scenery in corresponding to the flight conditions at every moment Thus an important part would be to focus on the signal and image pro cessing Indeed the pulse detection in presence of noise as well as the feature extraction from LADAR pictures are two wide fields of ongoing research Ad vanced work could be carried out in these directions using 7 17 18 19 Finally the current work could be extended by implementing some other functionalities For example the number of receiver s cells may be increased and thus a whole array of detectors could be used see 19 for discussions about the 3D focal plane array Furthermore the detection method may be expanded by implementing a coherent detection method based on the decription given in 10 The way leading to an exhaustive simulator might be tediously long fortunately for the reader only the paramount elements of the boundless list are presented here Acknowledgements Through my supervisor Patrick Hagl n I would like to thank all the persons from Saab Bofors Dynamics who made this master s thesis possible Further more I thank my examiner from KTH Bo Wahlberg I w
11. merged onto one unique final pixel P at distance d 3 4 Airborne Laser Scanning The detector is made of one receiver cell This implies that one pixel of the final LADAR image is obtained for each laser shot Consequently the scenery needs to be scanned by the laser beam in order to build pixel after pixel the LADAR image The following presents the basic formulas concerning airborne laser scanning in order to understand some basic principles used in the LADAR simulation The reader will find more detailed descriptions in 15 16 The scan method chosen produces a Z shaped scan as presented in Figure 3 4 There are four main parameters influencing the performances of a Z shaped scan 24 CHAPTER 3 SIMULATION Footprint Target LADAR rangeimage image Footprint Target range image LADAR image subarea pixel pixel e Figure 3 3 Simulation principle PRF the Pulse Repetition Frequency how often a pulse is sent Fs the scan frequency to go from left to right swath border or the opposite V the velocity of the platform S the swath width 3 4 1 Footprint Before all lets start by giving the formulas related to the laser footprint All the notations and symbols are reported in Figure 3 4 and Figure 3 5 The two cross range dimensions of the laser footprint are given by 2 en on fete 0 wam L 2R tan 53 h ith R Y sind where l l footprint cross range dimension
12. of view A low pass filtering with cutting frquency B is applied AP Ae Je Ol to all the in coming signals including the noise units MHz ceil_range ceil range edit set ceil range ceil range is the distance after which the detection is enabled nothing can be detected from the laser oO A o source to the distance ceil range units m Detection algorithm detect popupmenu select the pulse detection method The user can use among 3 different pulse detection methods 1 CFD Constant Fraction Discrimination Detect the received pulse using the zero crossing of a S shape pulse obtained from the received pulse 2 CFD 50 Constant Fraction Discrimination Detect the received pulse using the zero crossing of a S shape pulse obtained from the received pulse Then use a 50 leading edge detection 3 Matched filtering use a match filter with its impulse oA A AP AP A 00 AP AP DP OP response equal to the time reverse laser pulse shape divergence angle thetay fwhm edit set thetay fwhm thetax fwhm and display the grid of the spacial distribution thetay fwhm is the biggest divergence angle of the oe laser source modelled as a slit The other divergence angle is equal to 1 10 of the biggest divergence angle oO Ae o units degree f sc f sc edit set E sd i se is the scanning Frequency used in che 219 238 scanning The corresponding period 1 f sc is defined as the de e o time to dr
13. ADAR for autonomous vehicle guidance hazard avoidance and obstacle detection e LADAR terrain mapping for space exploration and autonomous vehicle navigation e Studies of advanced LADAR missile seekers and intelligent proximity fuzes guided missiles of type LOCAAS or E COM The simulation program presented in this report is as a first step in the direction of future full simulation softwares for 3D laser imaging A suggestion would be to converge with the work done by Ove Steinvall in 2 and use the 47 48 CHAPTER 6 REFLECTIONS model layout presented in Figure 6 1 as a reference for the future develop ments of 3D laser imaging simulators Scene description gt Platform speed traveled distance altitude looking angle PRF scanning frequency FOV gt Target shape orientation ie Generate position reflectivity a he Y y LADAR range images gt Propagation atmospheric attenuation Range detection Laser source CFD matched filter pulse shape width 4 power gt spatial distribution gt divergence Create the gt noisy reflected waveform in every footprint Receiver gt receiver aperture gt system efficiency Components pulse disassembly gt sampling frequency space and time distributions gt noise level amp bandwidth Figure 6 1 Development of a 3D LADAR imaging simulator inspired from the work of Ove Steinvall found in 2 and
14. D method This interpretation becomes more and more true for increasing noise levels 5 3 Footprint Size and Resolution Figure 5 3 shows two images with two different divergence angles all the other parameters are the same than in Figure 5 1 m Scanned image range image Scanned image range image Figure 5 3 LADAR images with divergence angles of 0 1 deg and 0 2 deg The footprint size can be modified by adjusting the laser beam divergence This permits finding a compromise between resolution and processing time Indeed to the footprint size corresponds directly the size of the pixels in the LADAR image Increasing the divergence increases the footprint size and then deteriorate the LADAR image resolution 5 4 Sampling Frequency and Range Accuracy Figure 5 4 is an illustration of the consequences of the sampling occurring at the receiver stage The lst image is the same than the LADAR image of Figure 5 1 where the sampling frequency is 1000 MHz This frequency has been decreased to 100 M Hz to generate the 2nd picture The influences of the sampling frequency on the range accuracy appear obvious in this picture Both pictures have the same cross range resolution x 44 CHAPTER 5 SIMULATION RESULTS m Scanned image range image Scanned image range image Figure 5 4 LADAR images with F 1000 Hz and F 100 Hz m N o pt o o a on co qm d 1 my a o Mm E
15. Gy 1 2 thetay_fwhm source diode model matrix creation thetax exp 2 thetax alphax 2 Gx row thetay exp 2 thetay alphay 2 Gy row lx y 1 R42 _thetax _ thetay Normalization x_y Ilx_y sum sum _x_y sr 2 Transpose to match to the xy axis description lxy lxy end end Plot if nargout find Maximum M max max l_x_y mesh xy xy I x_y title Normalized irradiance distance num2str R xlabel x m ylabel y m axis 0 6 L 0 6 L 0 6 L 0 6 L O M end Figure B 2 Source diode model 2 2 63 Appendix C Pulse detection the CFD algorithm m file The following figures numbers C 1 C 2 and C 3 stand for the m file contain ing the Matlab function which runs the CFD algorithm Actually both the CFD and the CFD 50 algorithms are contained in this m file The example provided in the description of this function provides the signals related to the CFD algorithm only 69 66 APPENDIX C PULSE DETECTION THE CFD ALGORITHM M FILE function timepeak valpeak CFD t pulse FWHM ceil_range trigger_time1 CFD returns the index and the value of the pulse s point corresponding to the main zero crossing of the S shape signal using the CFD Constant Fraction Discrimination method Setting detect to CFD_50 modify the CFD method by applying a CFD 50 leading edge detection indexpeak peak CFD t pulse FWHM ceil_ range
16. LADAR Proximity Fuze System Study Ga ge Ye ERIC BLANQUER KTH Soy woe KTH Electrical Engineering Master s Degree Project Stockholm Sweden April 2007 XR EE RT 2007 009 111 Abstract LADAR Laser Detection and Ranging systems constitue a direct extension of the conventional radar techniques Because they operate at much shorter wavelengths LADARs have the unique capability to generate 3D images of objects These laser systems have many applications in both the civilian and the defence fields concerning target detection and identification The extraction of these features depends on the processing algorithms target properties and 3D images quality In order to support future LADAR hardware device developments and system engineering studies it is necessary to understand the influences of the phenomena leading to the final image Hence the modelling of the laser pulse propagations effects reflection properties detection technique and receiver signal processing have to be taken into account A complete simulator has been developed consisting of a graphical user interface and a simulation program The computer simulation produces simulated 3D images for a direct detection pulse LADAR under a wide variety of conditions Each stage from the laser source to the 3D image generation has been modelled It yields an efficient simulation tool which will be of help in the design of the future LADAR systems and gauge their per
17. Propagation and reflection 1 D Model LASER P 2 MOsp Q Y Receiver Model Signal and image processing Model Target features extraction Model I Figure 3 2 Modules repartition 3 3 Simulation Steps Procedure The key of success in the LADAR simulation is the decomposition of the laser beam in time and space The components disassembly presented in Equation 2 2 page 6 has been derived from 3 4 7 It represents the core of the simulation program The main idea is that one laser shot provides one pixel of the final LADAR image The pixel has same resolution as the size of the laser footprint and is obtained using one single pulse The simulation steps are presented in the following and stand for the tremendous amount of lines of code Figure 3 3 gives a schematic view of the principles used 22 CHAPTER 3 SIMULATION 1 Define all the parameters required for the simulation concerning the platform laser source atmosphere target noise level and receiver 2 For every laser shot create the laser pulse in time and create the laser footprint in space about to illuminate the pixels on the 2D range image p t laser pulse shape in time I x y laser footprint on the target irradiance at target range 3 Match the resolution of the 2D range image describing the target with the grid corresponding to the laser beam profile in the spatial domain lt gt the footprint Indeed as stated in Section 2 2 an
18. _x_y IRRADIANCE of the source diode model at a target distance R Example global thetay_fwhm global thetax_fwhm thetay_fwhm 0 2 thetax_fwhm thetay_fwhm 10 source diode xy _02 50 2000 See also Simulation_051 Simulation_071 pixel_shot Copyright 2006 2007 Eric Blanquer ericblanquer hotmail com Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Vo Yo Yo Yo Yo Yo Yo Yo Yo Yo Y Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Yo Vo Function global thetax_fwhm global thetay_fwhm Gx 1 SuperGaussian coefficient must be gt 1 Gy 5 SuperGaussian coefficient must be gt 1 if Gx lt 1 error ERROR Gx must be gt 1 else if Gy lt 1 error ERROR Gy must be gt 1 else definition of the footprint dimensions using the FWHM angles 11 2 R tan thetax_fwhm pi 2 180 12 2 R tan thetay_fwhm pi 2 180 take the largest dimension to create a SQUARE shaped pixel L max 1 12 L ceil L 1000 1000 sr L sqrt nsa spatial resolution if nsa lt 50 Figure B 1 Source diode model 1 2 error ERROR choose a bigger nsal elseif nsa gt 10000 error ERROR choose a smaller nsa end xy L 2 sr L 2 xy spatial variable change of variables thetax xy R 1 3 xy R 43 pi 180 thetay xy R 1 3 xy R 43 pi 180 angle conversion alphax 2 log 2 4 1 2 Gx 1 2 thetax_fwhm alphay 2 log 2 4 1 2
19. ampled through an A D Analogic Digital converter at the sampling frequency Fs This permits the reducing of the amount of data to be processed and thus reduces the computation time e High F provide better range resolutions in every pixel but increase the pixel processing time As a consequence the PRF developed in 3 4 becomes lower the final image has poor resolution but good precision in every pixel e Low F give bad range resolution but decrease the pixel processing time As a consequence the PRF developed in 3 4 becomes higher the final image has good resolution but poor precision in every pixel Consequently a compromise has to be found between the cross range dimension accuracies resolution and the range dimension accuracy pixel precision To be able to study this problem the parameter F is included in the LADAR simulation However the computation time depends much on the algorithms and hardware used at the processing stage Therefore this is hard to predict and only F appears in the simulation allowing to experience different range precisions 2 5 3 Noises amp Noise As in all conventional optical systems the LADAR receiver is subject to several noise sources ambient backgrounds detector dark current thermal noise and quantum shot noise Once again most of these perturbations are closely related to the con struction of the receiver which is unknown More than 15 parameters have to be
20. are closely related to the LADAR image resolution Point spacing along the track The distance between the two extreme points on the same line of scan see dalong in Figure 3 4 is given by V lalong F 3 5 SC where dalong See Figure 3 4 28 CHAPTER 3 SIMULATION Fc scan frequency V velocity of the platform Its yields the range point spacing dal ae a 3 6 where Zalong is the distance between two points in the range direction see Lalong in Figure 3 4 Point spacing across the track Using the swath width S derived in Sec tion 3 4 2 it yields 5 across vr 3 7 across 3 7 where Zacross 18 the distance between two points in the direction orthogonal to the range direction see Zacross in Figure 3 4 3 5 Signal Processing and Pulse Detection In theory the idea of computing the range to an object by measuring the time of flight of a pulse is an efficient method Nevertheless in reality it depends much on how the measurements are done and thus on how the pulse is detected In the LADAR simulation the user can choose between three methods The first two are based on a direct use of the temporal shape of the received waveform The last one uses a filtering method 3 5 1 CFD CFD stands for Constant Fraction Discrimination It is a cost efficient algorithm which permits to detect a noisy pulse with good accuracy The following description is directly taken from the well
21. are as previously defined Since the divergence angles Orunm i are small 0 5 deg the approximation in Equation 3 2 is valid It shows the direct proportional relation between the target range R and the footprint dimension l Doubling the distance R or the flight height h will increase the footprint area by a factor 4 3 4 2 Swath Width The following equations based on Figure 3 4 give the swath width as a function of the altitude and the field of view 3 4 AIRBORNE LASER SCANNING 27 S 2R tan gt S Rx gt gt X y 3 3 where S swath width y LADAR s field of view all the other terms are as previously defined Equation 3 3 reveals the linear relation between the height of flight h as well as the target range R and the swath width S One sees that doubling the flight height will also double the swath width 3 4 3 Number of Points per Scan Line While the laser beam scans from one side to the other laser pulses are sent at a frequency PRF in order to create the pixels of the LADAR image The number of points per scan line is given by _ PRF N Fsc 3 4 where N number of points per scan line PRF Pulse Repetition Frequency Fy scan frequency Note in Equation 3 4 the independence of N regarding the flight height h and the target range R as well as the swath width S 3 4 4 Point Spacing The formulas related to the point spacing are given in the following They
22. aw one line from left to right OR from right to left units Hz Flight distance dim a edit ser dim a the travelled distance dim is the distance travelled by the platform during its scanning This distance is linked with the platform speed V and represents also the length of the final LADAR image HP AP Ae o Figure A 2 Help file 2 5 58 APPENDIX A PARAMETER DESCRIPTION units m FOV dim b edit ser dim b the FOV dim b is the Field Of View of the LADAR system It is defined by the angular aperture of the scanning The scanning is done on a transversal angle from dim b 2 to dim b 2 It influences the width of the final LADAR image units degree Fs _ Fs edit set Fs and plot the sampled pulse Fs is the sampling frequency used at the receiver in the pulse acquisition This is done to simulate the A D conversion units MHz FWHM _ FWHM edit set FWHM and plot the pulse FWHM is the Full Half Width Maximum of the pulse and is used to define the duracy of the pulse units ns looking angle looking angle popupmenu set looking angle display the distance to the target and the suitable 2D range images lists looking angle is the angle of view of the laser system taken from the horizontal The value 90 corresponds to a vertical scanning directly under the plateform units degree nsa nsa edit set nsa and display the grid of the spacial distribution nsa is the
23. cted powers ne with the same time indices 2 It results a temporal signal which is the impulse response h of the considered pixel P hpi D Pi subk 1 1 hp i impulse response of Py see appendix B for the creation of the source diode model It contains the m file including an example 3 4 AIRBORNE LASER SCANNING 23 6 Convolve the impulse response hp with the temporal laser pulse p t to form the reflected power detected by the receiver This corresponds to the total received power for the considered pixel P Ppt t hp t Lop t 00 I he x piL 7 ae where a total received power from P Io laser pulse power Note that according to Section 2 5 3 page 14 Bet k x p t for all k ER 7 Let the Gaussian noise disturb the total received power according to the SNR set up by the user The signal x t obtained is used in the pulse detection x t Ppa t n t n t additive Gaussian noise with a standard deviation o NEP x t noisy reflected pulse from Pp 8 A pulse detection algorithm determines from the signal x t the round trip time of the pulse reflected by the pixel P see Section 3 5 page 28 for the details about the pulse detection algorithms 9 The latter permits to compute the distance d to the pixel P using Equa tion 2 1 The value d is assigned to the corresponding pixel on the final LADAR image all the subareas constituting the original footprint are
24. d EY eS 30 Matched NET von ju a 2 ed Geb Oe he eee A eg 30 Dereensho r LADAR GUL amp 54 28 3 da pe AA eee 3 31 Front panel sa 2 Sa nS IE AI Bir Bee a 39 Pixel simulation Ist Low eor a ok ai SAN Dre ea 39 Pixel simulation 2nd row with CFD 39 Pixel simulation 2nd row with matched filter 36 Simulation ideal Case evo a Es Sp abe Aig Sa FOR e 37 Simulation Zig Zag scanning a mean Sod ae aE DAY dits 37 Classical LADAR image 41 LADAR images with CFD and matched filter 42 LADAR images with divergence angles of 0 1 deg and 0 2deg 43 LADAR images with F 1000 Hz and F 100 Hz 44 LADAR image using Zig Zag scanning 44 Development of a 3D LADAR imaging simulator 48 Help lei wee seek ns De oh a ar ach o eG ee co 56 vil vill A 2 A 3 AA A 5 B 1 B 2 C 1 C 2 C 3 List of Figures Help Ml 5 RS me eed ee ee ac Boah a 57 Peller aoe ete Bea ee Oe ee oe ee 58 Help ale 110 ws a e Oe GAO AR Be Soe BS ee Be Oe ed 59 Helpe be 24 2 4 2 22 keh oe 2h a SS eee Phe Ease 60 Source diode model 1 2 aa uw ere we Se Dee Hee BS ES 62 source diode model 2 2 nun 4 u 5 ER sat ana es 63 CED SlEOr hm SE eri sha Se a e BSE ee Me oss 66 CED algorit h 2 3 LS SELS USD RES ee ee a Se eS 67 OD alcobas ds er na eRe oe A 68 Part Background amp Basis Chapter 1 Introduction 1 1 Background During World Wa
25. d developed in Section 3 1 the laser beam profile is decomposed in its cross range dimensions x y Each cross range component or subarea corresponds to the energy contained in a square typically 1 x 1 em at target range The user can choose the number of subareas within the laser footprint The size of the subareas depends on their quantity the target range and the beam divergence Consequently it is necessary to adapt the resolution of the 2D range image to the subareas decomposition for the next steps of the simulation At the end of this step each subarea of the footprint has the same dimensions as the pixels of the 2D range image describing the target 4 Consider one pixel P In order to compute the waveform of the reflected pulse one needs first the impulse response hy of P Then send one Dirac t one sample of amplitude one on P and apply the LADAR range equation in each subarea contained within this pixel The latter meaning compute the reflected power from each subarea reaching the receiver For every subarea a value Po is obtained where 2 is the round trip time with respect to the subarea k The slope is not a parameter taken into account during the reflection each cross range component is treated as if it encounters a subarea that is perpendicular to the line of sight to the sensor However a pulse gt 1 y may see non perpendicular surfaces as a set of subareas at different ranges 5 Sum the refle
26. depends on the footprint size which may change in the simulation Actually the user can set up the number of subareas constituting the footprint see paragraph entitled OPTIONS in 19 20 CHAPTER 3 SIMULATION Section 4 1 1 the direct consequence being a resolution change Nevertheless with the default parameters the spatial resolution is 1 x 1 cm Generally speaking the resolutions have been chosen according to the computer power available nowadays and to generate time efficient results with good accuracy 3 2 Overview and Modules Description The reader is reminded here of the process decomposition found in Figure 2 1 page 5 in order to have a clear view of the principle It is a good schema to review before reading the explanations of the different LADAR simulation modules The simulation program is entirely written in Matlab It consists of several modules passing data from one to the next by variables Two kinds of variables are found in the program i the global variables correspond to the parameters set up by the user or fixed values which will not change during the execution ii the intern variables subject to modifications are passed through the input output arguments of the different modules Figure 3 1 presents these main modules associated to their principal parameters and concepts They are organized in the logical order in which they appear in the simulation program Target shape target orientation target po
27. documented book 10 and is related to the Figure 3 6 taken from 10 CFD is accomplished by splitting the incoming signal into two chan nels delaying one channel by one half of a pulse width and subtracting the delayed channel from the original This results in a positive and then negative signal with a characteristic S shaped profile It has been shown that the zero crossing of this derived signal is very insensitive to amplitude fluctuations It is however somewhat sensitive to pulse length variations the m file including an example related to the CFD algorithms is found in the appendix C 3 5 SIGNAL PROCESSING AND PULSE DETECTION 29 The zero crossing of the S shaped profile seen in Figure 3 7 is used to trig a timer The CFD algorithm is applied to the sent pulse to start the clock and then applied to the received pulse to stop the clock This provides a time directly used in the range computation 3 5 2 CFD 50 The principle of the CFD 50 method is based on the idea of the 50 leading edge detection The latter consists in taking the reference time at a time where the leading edge of the pulse reaches 50 of the pulse s maximum In some cases it permits to detect more details than with a basic method based on the detection of the pulse maximum as demonstrated in 1 So does the CFD 50 method as illustrated in Figure 3 7 to the zero crossing of the S shaped profile corresponds a value on the pulse yo not
28. e 4 2 axes are used to display graphs and images When it is useful a graphic is displayed illustrating the effects of the new set up parameter Every time that the user changes and validates a value a graph is displayed within these axes For example it could be the new target image the profile of the laser beam or the sampled signal Under the axes there are the 4 parameters related to the receiver Firstly the receiver s bandwidth can be modified with the edit element entitled B Secondly the signal to noise ratio at the receiver can be changed in two ways directly by typing a value in the edit element named SNR or using the slider its value is then displayed in the edit element Furthermore the detection algorithm used in the signal processing can be selected thanks to the pop up menu made of three items CFD CFD 50 and matched filtering Finally the sampling frequency is set up in the edit element named F The bottom line entitled 2D range images displays the lists of the images avail able to be used as target and the images of the library The content of these two lists is set according to the set up looking angle The field target contains the im age to be scanned in the simulation and the field library is the image used to do a comparison with the LADAR image of the target see Section 4 3 to find details on the comparison done 4 1 3 Front Panel Right Side On the right side of the front panel one find
29. e that it is not the maximum the reference time is then taken when the leading edge of the pulse reaches 50 of yo Empirically the CFD 50 method gives substantially better results than the CFD method 3 5 3 Matched Filter The matched filter principle is used extensively in pattern recognition and signal detection It is the optimal linear filter for maximizing the signal to noise ratio SNR in the presence of additive stochastic noise n Given a transmitter pulse shape p t of duration T the impulse response hopt of the matched filter is given by hopt t k x p T t for all k E R 3 8 Equation 3 8 shows that the duration and the shape of the impulse response of the optimal filter is determined by the pulse shape p t Aopt t is a scaled time reversed and shifted version of p t Differential Amplifier N A T V Figure 3 6 CFD peak detection Zero Crossing Detector Delayed and Inverted Signal Inverter 30 CHAPTER 3 SIMULATION 08 Fo a cues u es CFDtimeref gt X CFD 50 time ref 2 1 5 1 0 5 0 0 5 1 1 5 2 Figure 3 7 CFD and CFD 50 This is applied in the LADAR simulation in which a pulse p is sent out and one wants to find something in the noisy reflected signal x similar to what was sent out The schema of the matched filtering is presented in Figure 3 8 p t x t rpx t n Figure 3 8 Matched filter The matched fi
30. eak50 end Plots if nargout plot t pulse r hold on Figure C 2 CFD algorithm 2 3 68 APPENDIX C PULSE DETECTION THE CFD ALGORITHM M FILE grid plot t_c pulse_s g plot t_c pulse out k plot timepeak valpeak r MarkerSize 20 plot t_c ceil_detection 2 0 mx MarkerSize 20 hold off V axis V 2 t end axis V end Figure C 3 CFD algorithm 3 3 Index atmosphere 11 bandwidth 15 Beer s law 11 CFD 28 35 42 cross range dimension 6 14 16 24 detection technique 13 discretization 19 efficiency 14 energy distribution 7 footprint 16 19 22 24 43 FWHM 8 10 Gaussian distribution 8 14 Gaussian profile 7 GUI 31 impulse response 22 30 irradiance 7 9 LADAR range equation 15 Lambert s law 13 Lambertian surface 13 16 laser diode 8 laser pulse 5 6 9 22 matched filter 29 36 42 NEP 14 23 noise 23 29 42 PRF 23 27 pulse shape 6 11 22 30 range dimension 6 14 range equation 15 22 range image 12 22 36 receiver 13 14 reflexion 12 resolution 14 19 22 27 43 sampling 14 19 43 SNR 15 23 29 42 spatial distribution 6 spatial resolution 20 subarea 22 target cross section 15 temporal distribution 6 temporal resolution 19 World War II 3 Zig Zag 44 The Author Eric Blanquer concludes with this Master of Science Thesis a double degree program Thanks to internationa
31. et Moreover one can approximate the solid angle 2 by a flat surface since the laser footprint has small dimensions That is to say the z dimension is neglected only the extensions along the x and y cross range dimensions are considered Thus the flat surface corresponds to the laser footprint on the target dA Q This assumption is valid because the divergence angles and the target range are small which gives to a small footprint area typically lt 0 1 m Finally under the previous approximations and substituting Equation 2 13 in Equation 2 12 lead to the LADAR range equation F t pD 4R where all terms are as previously defined P SI No 2 14 The initial microwave radar range equation reduces into a simpler form Equa tion 2 14 that the reader can find in 4 5 7 It provides good insight on what happens with the optical power P during its propagation T is the two way attenuation factor caused by the particles and gases present in the atmosphere p represents the proportion of power reflected by the target and nsyst the efficiency of the system D characterizes the aerial extension of the receiver which collects the reflected power Equation 2 14 also shows the typical dependence for extended targets of the received power with the inverse square of the range Part Il The Simulation Software Chapter 3 Simulation The LADAR simulation has been developed to support future LADAR hardware
32. foot print pattern has a perfect match with the scanned area The foot prints do not overlapp or are not disjoint The scanning covers the whole image It is based on a one cell receiver 2 Zig Zag scanning this is the realistic scanning in which v f sc and PRE are taken In to account In case of overlapping foot prints the average is computted on the common area It is HP AP AW CP A 00 CP based on a one cell receiver Figure A 5 Help file 5 5 Appendix B Creation of the source diode model m file The following figures numbers B 1 and B 2 stand for the m file containing the Matlab function which creates the source diode model used in the simulation Ihe example provided in the description of the function is a stand alone example and can be run by the reader once the m file has been reproduced 61 62 APPENDIX B CREATION OF THE SOURCE DIODE MODEL M FILE function I_x_y L source_diode_xy_02 R nsa SOURCE_DIODE_XY_02 creates the NORMALIZED IRRADIANCE of the source diode model in the x and y coordinate system at a target distance R The target range is take into account in the function profile R dependent since the profile is attenuated by a factor R 2 l_x_y source_diode_xy_02 R nsa source diode xy 02 R nsa plots the normalized irradiance INPUTS R target range nsa number of sub areas constituting the footprint 6 OUTPUTS
33. form Ta exp az 2 10 where Ty one way attenuation factor a atmospheric extinction coefficient in mt z range dimension Since the laser pulse travels twice the distance to the target before reaching the receiver it is affected by Ta x Ta T The Figure 2 6 shows a plot of the squared attenuation factor 2 4 Target Interactions The interactions between the laser beam and the surface of the target result from complicated processes hard to model It depends on two main characteristics of the surface its slope and its microscopic properties For detailed discussions about target interaction and reflection the reader will refer himself to 1 7 12 In the following the target modelling done in the LADAR simulation is explained and followed with the description of the target reflection process 2 4 1 Target Modelling As it has been shown previously the range from the laser source to the target plays a preponderant role in the LADAR simulation For this reason the target has to be modelled in terms of distance The LADAR system is on board a platform 12 CHAPTER 2 LASER BEAM PROPAGATION THEORY This platform is flying at a constant altitude following a straight trajectory and with a constant forward looking angle The dimensions of the target to be scanned being much smaller than the flight altitude the assumption is that the scenery can be considered as seen from a fixed point of view That is to say that t
34. formances This master s thesis contains the theoretical background about laser used to build the simulation program The latter is described schematically in order to provide an insight for the reader The graphical interface is then presented as a short user s manual Finally in order to illustrate the possibilities of the simulator a collection of selected simulations concludes the report Keywords LADAR laser radar laser scanning range image pulse detection mod elling simulation graphical interface Matlab iv Saab Bofors Dynamics Saab group is a high technology company that offers world leading system solutions services and products in defence aviation space and civil security Saab s business op erations are carried out by some fifteen business units that report directly to the group management Saab Bofors Dynamics is one of the business units and represents a vital part of Saab s defence activities with approximately 1100 employees Operations at Saab Bofors Dynamics consist of two core activities designated as missiles and support weapons As a consequence Saab Bofors Dynamics provides complete missiles solutions The activities especially in the area of missiles are technologically and productively based on the requirements and needs of the Swedish defence forces Consequently a close collaboration with the Swedish defence forces has been developed On top of this it also participates in many internatio
35. from 1 The chapter structure follows this decomposition Firstly the laser method is re viewed Secondly the next section focuses on the laser source and describes the energy distribution of the beam number 1 Next the modelling of the propaga tion in the atmosphere is explained number 2 Then the interactions with the target are presented the modelling of the target is described before explaining how the reflection phenomenon works number 3 Finally the receiver model is exposed number 4 and the LADAR range equation derivation concludes this chapter PHE TARGET v Figure 2 1 Process decomposition 2 1 Laser Method and Range Finding Principle The principle of the laser range finder is shown in Figure 2 2 figure directly inspired from 2 A laser pulse is sent out from the laser source transmitter and travels in 5 6 CHAPTER 2 LASER BEAM PROPAGATION THEORY Figure 2 2 Laser range finding principle the air The pulse is then reflected on a surface element which can be the target the ground or an object The reflected pulse is collected by the receiver and corresponds to the received signal Thus the pulse travels twice the distance to the target turn and return Finally knowing that the pulse travels at the celerity of the light and measuring the time of flight of the pulse one computes the distance to the surface element using the formula At c NN where dtarget is the d
36. gure 4 3 Laser Pulse transmitted t Laser Pulse received Optical power 0 0 5 1 1 5 2 2 5 3 3 5 4 Time s x 10 Time s x 10 Figure 4 3 Pixel simulation 1st row The 2nd row shows two graphs which depend on the detection algorithm selected CFD algorithms or matched filter algorithm CFD Algorithms To the CFD algorithms CFD and CFD 50 correspond the plots of the two significant curves of the method the input pulse and the S shaped profile with its zero crossing see the algorithms descriptions in sections 3 5 1 and 3 5 2 Thus the first plot contains these two curves for the sent pulse and the second plot as well but with respect to the sampled noisy received pulse see Figure 4 4 Moreover the red on the pulse corresponds to the triggering time amp the zero crossing of the S shaped profile used for the range computation On the other hand the magenta x is the limit after which the detection is enable amp the ceil range option described in Section 3 3 Triggering time 1 7 Time s x 10 Time s x 10 Figure 4 4 Pixel simulation 2nd row with CFD 36 CHAPTER 4 GRAPHICAL USER INTERFACE Matched Filter Algorithm To the matched filter algorithm correspond the plot of the impulse response and the plot of the filter output see the algorithm description in Section 3 5 3 Moreover the red located at the maximum of the filter output fy described in Section 3 5 3 stands for the
37. h 1000 MHz so that it does not influence the result The pulse detection algorithm used is the CFD algorithm 5 2 Noise Addition and Detection Algorithms Figure 5 2 illustrates the performances of two detection algorithms in presence of noise From Section 5 1 only the SNR has been changed and its value is 3 Absolute range error Scanned image range image lt MSE gt 0 642 Scanned image range image Figure 5 2 LADAR images with CFD and matched filter On one hand the Ist row of graphics is obtained with the CFD algorithm On the other hand the 2nd row of graphics is obtained with the matched filter algorithm The curves on the right side of the figure are generated thanks to the pixel simulation to detect a surface at 57 55 m From these results the matched filter appears to be more efficient than the CFD algorithm This comes from the fact that the matched filter is not affected by the Gaussian noise by construction It is a robust method with 5 3 FOOTPRINT SIZE AND RESOLUTION 43 respect to white noise This is shown by the signals in Figure 5 2 In the CFD method the timer is trigged using the received pulse which is distorted by the noise As a consequence the time and then the distance computed are not accurate On the other hand the output of the matched filter is not modified by the noise addition The maximum can be detected without any extra error and leads to a more accurate result than in the CF
38. he scenery s distortion due to the platform s motion is not taken into account It yields that the 3D description of the scenery containing the target can be modelled by a 2 dimensional picture while working with a fixed forward looking angle This 2D picture is adapted in function of the angle of view that is to say it is changed when the forward looking angle is modified After having frozen the 3D scenery description into a 2D picture according to the forward looking angle the LADAR simulation needs the distance to each point of the 2D picture Here appears the concept of range image each pixel contained in the image has the value of the distance to an arbitrary origin the expressions distance image or range template are also used in the literature In the LADAR simulation this origin is the laser source Thus the pixels values represent the range to the laser source Figure 2 7 is an example of range image in which the brightness decreases with the range The generation of the range images is done via an external program It is based on a 3D description of the target from which one can specify the visualization parameters orientation distance resolution Thus the program displays the range image with respect to the distance to the camera which in our case is equivalent to the laser source 2 4 2 Target Reflection As stated before the reflection of the laser beam on a surface depends on the slope and the micr
39. igure 2 4 shows the irradiance of Equation 2 6 at a distance R 50m with the divergence angles OFWAHM 0 02 deg and Orwum 0 2 deg Note that I x y is normalized to unity in the simulation as stated with Equa tion 2 2 in order to keep a constant total power independently of the target range 2 2 2 Temporal Distribution Pulse Shape The time propagation of the laser signal is modelled as pulses Two models found in the literature have been selected to be used in the LADAR simulation In the 10 CHAPTER 2 LASER BEAM PROPAGATION THEORY first one the laser pulse travels with a time propagation which has been modelled in 7 as p t t 7 exp 2 Ty 2 ae 2 8 er 22 where 7 is the Full Width at Half Maximum FWHM of the pulse Assuming that one works with a constant signal power if 77 2 is decreased the pulse becomes narrower and will look like a peak This peak is detected and may be interpreted as noise by the receiver which fails in detecting this pulse if T 2 is increased the pulse will be flatter and may not reach the detection ceiling The receiver fails in detecting this pulse A compromise has to be found and the designer engineer can discover different properties of the laser pulse changing 71 2 This model is the most accurate one and is used in 1 2 7 8 A plot of Equation 2 8 is shown in Figure 2 5 plain line curve Model 1 Model 2 Optical power W
40. ion The intensity of an optical beam is not constant across its diameter at all ranges see Figure 2 3 taken from 5 The irradiance corresponds to the power of electro magnetic radiation incident on a surface and has the unit of W m7 It represents the energy profile of the laser beam in the space This profile depends on the tech nique used to generate the laser light diode lasers solid state lasers micro chips lasers However the shape of the emmitter has more influence on this energy profile In the LADAR simulation the laser light is obtained from a semi conductor laser diode which its emitting area is a slit Before describing its model the pre liminary step is to derive the model of the most common case where the profile is Gaussian The Gaussian Model The Gaussian profile is obtained from a transmitted beam that uniformly illuminates a circular output aperture That case is shown in Figure 2 3 and the irradiance follows the expression developed in 5 I r Ip exp 2 3 where the variable r is the distance measured in a transverse plane from the central axis of propagation z w is the beam half width and represents an arbitrary Figure 2 3 A Gaussian beam 8 CHAPTER 2 LASER BEAM PROPAGATION THEORY boundary to the beam s width By definition at r w the beam s irradiance is Io e 14 Ip and most of the energy resides within this imaginary cylinder of radius w as represented in Figu
41. istance from the laser source to the target At is the time of flight of the pulse round trip time and c the celerity of the light dtarget 2 1 2 2 Energy Distribution Space and Time To be able to describe the phenomenon the laser pulse has to be modelled in time 1 dimension as well as in space 3 dimensions which leads to a 4 dimensions model Fortunately the pulse is separable in a temporal and a spatial distribution They are together expressed as the intensity U x y z where x and y are the vertical and horizontal cross range dimensions and z is the range dimension the direction that the pulse is travelling These three variables x y z are shown in Figure 3 5 The expression can be found in 1 3 4 as follow U z y 2 V z x Hz y V ct x I x y 2 2 o p t x I x y where 10 is the total pulse power x y is the proportion of energy contained within a component located at x y p t is the discrete pulse shape in the range 2 2 ENERGY DISTRIBUTION SPACE AND TIME T dimension The integrals of I x y and p t are both equal one because they are normalized to unity x y and z amp t take on discrete values The next two sections specify the terms in Equation 2 2 Section 2 2 1 refers to I x y which is the spatial distribution of the energy namely the irradiance and Section 2 2 2 describes the temporal energy distribution of the pulse p t 2 2 1 Spatial Distribution Irradiance Funct
42. l agreements between France and Sweden he is about to receive two diplomas the Master of Science in Systems Engineering from KTH the Royal Institute of Technology of Stockholm Sweden and the Master of Science in electrical engineering from INPG the Grenoble Institute of Technology France His studies include automatic control signal processing system study simulation and modelling 7 ericblanquer hotmail com 46 70 474 95 67
43. l_ time 2 ceil_time flight time of the pulse to the ceil range ceil_ detection ceil ceil_time delta ceil s index The detection is disabled untill the ceil_ detection pulse_c pulse ceil_ detection end zeros 1 ceil_detection 1 t_c t ceil_ detection end 1 length t ceil_ detection 1 length t delta The pulse is shifted of shift and mirrored pulse_s pulse_c shift end zeros 1 shift 1 Addition with the original pulse S shape resulting signal pulse out pulse c pulse s Use of the function crossing to get the zero crossing index ind crossing pulse_out t_c all the zero crossings MPoints of the original pulse corresponding to the zero crossings timepeaks t_c ind valpeaks pulse_c ind Select the pulse s point corresponding of the main zero crossing of the S shape signal valpeak indtimepeak max valpeaks timepeak timepeaks indtimepeak CFD amp 50 leading edge identical to CFD but one computes the point at 50 of the pulse s point corresponding of the main zero crossing of the S shape signal if stremp detect CFD_50 1 indextimepeak find t timepeak pulse50 pulse 1 indextimepeak t50 t 1 indextimepeak ind50 crossing pulse50 t50 50 100 valpeak timepeaks50 t ind50 valpeaks50 pulse ind50 valpeak50 valpeaks50 length valpeaks50 timepeak50 timepeaks50 length timepeaks50 timepeak timepeak50 valpeak valp
44. le users to enter or modify parameters values Each new value must be validated by pressing enter e pop up menu pop up menus open to display a list of choices when pressed When not open a pop up menu indicates the current choice e push button push buttons generate an action when pressed To activate a push button click the mouse button on the push button e slider sliders accept numeric input within a specific range by enabling the user to move a sliding bar The user move the bar by pressing the mouse button and dragging the pointer over the bar or by clicking in the trough or on an arrow The location of the bar indicates a numeric value which is selected by releasing the mouse button e radio button radio buttons are useful when providing the user with a number of independent choices They are mutually exclusive within a group of related radio buttons i e only one is in a pressed state at any given time To activate a radio button click the mouse button on the object The state of the device is indicated on the display 4 1 1 Front Panel Left Columns The left side of the front panel gathers simulation parameters as seen in Figure 4 2 Every line is made up of one tert element giving the name of the parameter that can be modified editing the edit element To be precise there are three exceptions to that format The 1st line permits to change the pulse shape using a pop up menu instead of an edit element Line 6 corre
45. lter is obtained by correlating a known signal p or template with the unknown signal x to detect the presence of the template in the unknown signal This is equivalent to convolve the unknown signal with a time reversed version of the template as shown in Equation 3 8 By time reversing p the convolution implemented by filtering is transformed into a sliding cross correlation operation between the input signal x and the sought signal p leading to fpr see Figure 3 8 The occurrences of p in x are detected in each peak of fpr Detailed plots of the filtering process are found in Section 4 For each occurrence corresponds a time used to trig a timer and then compute the round trip time of the pulse Chapter 4 Graphical User Interface The Graphical User Interface GUI is the link between the user and the code This gives an efficient way of working without interacting directly on the simulation program Knowing that one picture says more than one thousand words the GUI s efficiency comes from i it is simple to use despite the comfortable level of abstraction of the simulation ii it is interactive thanks to the numerous plots displayed at every parameter change or simulation runs done by the user iii the user has a constant overview of all the parameters used Pune sape feet w Laser Pulse with cone Pret ne 100 CP y u y y y y Putre power WV 00 SE LA j Draco unge eg os LASER SE AM f t mn 5
46. n Technique 14 2 5 2 System Efficiency and Sampling Frequency 14 20 9 Noises amp ANOLSO ee e 3 5 2 0 ke wa OAS a ta RES See a 14 2 6 LADAR Range Equation xd at NT Serre dE eee 15 II The Simulation Software 17 3 Simulation 19 3 ADISCTEUIZACIONL zur a E AS Dr BEE 19 3 2 Overview and Modules Description 20 3 3 Simulation Steps Procedure 2 vi 3 4 Airborne Laser Scanning ors EOotprint LOL 4 206 4 etre eos 341 2 Swat lie WIth de o SN BR we BOS 3 4 3 Number of Points per Scan Line 3 4 4 Pomp Spacin lt 642 24 4 645464 di 3 5 Signal Processing and Pulse Detection Boek Cobras 2 tne oe SE SG Be 3 a ee 393 2 CEDSOR 3 6 ee 2 u ae a a BS a i 3 5 3 Matched Filter seco dg be De ao de aK ee 4 Graphical User Interface Le Bront Panel os de ren a de Ar Hote od ee Be 4 1 1 Front Panel Left Columns 4 1 2 Front Panel Central Elements 4 1 3 Front Panel Right Side 4 2 Visualization Panel 4 2 1 Pixel Simulation 2 82 sure me bow sh ss 4 2 2 Simulation LADAR Image Generation 4 3 Workspace Indications III Results amp Reflections 5 Simulation Results 5 1 Classical LADAR Image 5 2 Noise Addition and Detection Algorithms 5 3 Footprint Size and Resolution 5 4 Sampling Frequenc
47. nal collaborations The company s fields of expertise are systems technology guidance and navigation modelling and simulation sensor technology and warhead and propulsion technology The sensor technology includes radar systems optoelectronic sensors and laser technology The latter being the center of interest of this master s thesis More precisely the work has been done within the section of electronics and software development land amp air defence a branch of the development and technology department Saab Bofors Dynamics Bofors industriomrade SE 691 80 Karlskoga Sweden description taken from the official company presentation of 2007 01 22 Contents Contents Vv List of Figures vii I Background amp Basis 1 1 Introduction 3 bil Background US 28 ER a eas AR SU aaa 3 PA AA a a BE BS NANO 3 LS Thesis Outline idea Oe a eee 4 2 Laser Beam Propagation Theory 5 2 1 Laser Method and Range Finding Principle 5 2 2 Energy Distribution Space and Time 6 2 2 1 Spatial Distribution Irradiance Function T 2 2 2 Temporal Distribution Pulse Shape 9 2 3 Propagation Atmospheric Effects 11 2 4 Target Interaction S ae e a We eek A Kar 11 2 4 1 Target Modelling eh RSS pe EU ad AN ess 11 2 42 Target Reflection e isa do Sn r ca a 12 2 5 Receiver Characteristics amp lt a ism ose ee es Las ot Pw hee 13 2 5 1 Detectio
48. nds to the model used in the LADAR range equation derived in Section 2 6 2 5 Receiver Characteristics The receiver is an important stage in all the LADAR systems It is characterized by the detection technique direct or coherent the area of the receiver element and the optical efficiency 14 CHAPTER 2 LASER BEAM PROPAGATION THEORY 2 5 1 Detection Technique The LADAR simulation uses the direct detection The receiver consists in a photo sensitive element which generates a signal directly proportional to the quantity of optical power received This technique contrary to the coherent detection uses a conventional passive optical receiver More details about detection techniques are found in 10 2 5 2 System Efficiency and Sampling Frequency The ability of the receiver to detect the incoming optical power is limited by the efficiency of each of its subcomponents Since it is impossible to know which kind of design has been used to build the receiver it is impossible to know every efficiency A previous estimation of the total loss due to the receiver has to be carried out before including it in the LADAR simulation The receiver efficiency appears as a simple coefficient a percentage that can be modified by to the user and called Nsyst It will limit the received power Another aspect which limits the performances of the LADAR system is the rate to acquire data used at the receiver The signals at the receiver are s
49. number of sub areas constituting one laser footprint It represents the grid used to describe the spacial distribution of the power units XXX PRF PRF edit set PRF PRF is the Pulse Repetition Frequency of the LADAR system It represents the frequency used to send laser pulses in the Zig Zag scanning units Hz Pulse power 10 edit set I0 and plot the pulse IO is the coefficient used to change the power of the laser pulse units W Pulse shape shape num popupmenu oe select the pulse shape and plot the pulse The user can choose between 2 different pulse shapes corresponding to 2 different mathematical expressions 1 tau FWHM 3 5 pulse t tau 2 exp t tau 2 pulse exp 4 loa 2 t 1 5 e 7 FWHM 2 AP Y oP A Figure A 3 Help file 3 5 59 receiver aperture _ r aperture edit set Y Aperture Y aperture is the radius aperture of the receiver units m SNR_____FACTOR edit set FACTOR and plot the noisy pulse FACTOR is the SNR of the received pulse Changing this value allows the user to simulate AP AP ol different amount of random noise zero mean noise units XXX SNR_slider noise param2 slider set FACTOR display the value and plot the noisy pulse This slider is another mean to change the SNR of the received pulse See SNR FACTOR edit for the details units XXX od A oP system efficiency ____ eta syst edit je set e
50. only a selection which is according to the author easily understandable by the reader Nevertheless the LADAR simulation offers a wider range of possibilities which is left to be discover by the future user From these examples one sees that it is possible to build a modelling tool for the laser target imaging which can predict the performances and results from LADAR systems The combination of the laser images with the simulated waveforms provides a powerful tool permitting to carry out detailed analysis Chapter 6 Reflections 6 1 Conclusions From the laser source to the optical receiver the simulator which has been developed models various stages of the whole LADAR imaging process The modular nature of the simulator permits to reproduce different conditions thanks to the wide choice in parameters The breaking of the pulse into com ponents and the use of 2D range images were the keys to success Thus the simulation can generate reflected pulses for any target shapes This modu lar simulation associated to its powerful graphical interface represents a pri mary engineering software This tool will permit to assist the design of future LADAR systems and to carry out performances tests A such modular simulator could be of good use in the following applica tions e LADAR UAV platforms using the 3D mapping capabilities to acquire 3D models of land and building e UAV 3D scanning LADAR for target identification e L
51. oscopic properties of the surface This affects the amount of electro magnetic radiation reflected as well as the directions in which the light is reflected In a primary approach these phenomena are not taken into account A constant 0 20 40 60 80 100 Distance m Figure 2 6 Squared attenuation factor T with a 0 01 2 5 RECEIVER CHARACTERISTICS 13 Figure 2 7 Range image of a tank T80 term p notably independent of the incidence angle is used and represents the total hemispherical target reflectance It is the percentage of re emitted electromagnetic power in the reflection As an example a white surface will have a bigger p than a black surface since the white surface re emits more light In Section 2 6 in which the LADAR range equation is derived the terms Lam bertian targets and extended targets are used These are directly related to the Lambert s law which is best described here as done in 13 Prefieeied 0 Po cos 0 2 11 where Preflected 0 is the intensity of a small incremental area of the source in a direction at angle 0 from the normal to the surface and Pp is the intensity of the incremental area in the direction of the normal Equation 2 11 says that the total radiant power observed from a Lambertian surface is directly proportional to the cosine of the angle 0 between the observer s line of sight and the surface normal The law is also known as the cosine emission law and correspo
52. ould like to pay special tribute to Ove Steinvall for his advanced work about laser technology Indeed this master s thesis contains many references to his work and would not have been as complete as it is without it My appreciation also extends to Tomas Carlsson for his professionalism and Anders Aslund who contributed to this work I acknowledge the assistance of Sorana Barbici who makes it all worthwhile ol References 11 O Steinvall and T Carlsson Three dimensional laser radar modelling Proceedings of SPIE Vol 4377 2001 2 O Steinvall Waveform simulation for 3 d sensing laser radar FOA R 00 01530 612 408 SE 2000 3 Q Zheng S Z Der and H I Mahmoud Model based target recognition in pulsed ladar imagery IEEE 1057 7149 01 Vol 10 No 4 2001 4 SZ Der B Redman and R Chellappa Simulation of error in optical radar range measurements Optical Society of America 0003 6935 97 276869 06 Vol 36 No 27 Applied Optics 1997 15 E Hetch Optics Pearson Education International 2002 6 ZEMAX user s guide ZEMAX optical design program chap 12 p359 360 2006 17 T Carlsson O Steinvall and D Letalick Signature simulation and signal analysis for 3 D laser radar FOI R 0163 SE ISSN 1650 1942 2001 8S O Steinvall Effects of target shape and reflection on laser radar cross sections Optical Society of America 0003 6935 00 244381 11 Vol 39 No 24 Applied Optics 2000 9 Encyclopedia of la
53. planations about every item of the GUI front panel They are listed at the beginning of the file and are presented in alphabetical order 99 56 APPENDIX A PARAMETER DESCRIPTION README is a help file SIMULATOR LADAR GUI is the graphical user interface of the LADAR proximity fuse simulation Here is the description of its parameters Run the simulator by running the m file SIMULATOR LADAR GUI m of NS AP ol BEEECEEEEEEEEEEEEEEEEEEEEEEEEEEECEEEEEEEEEEEEEEEESS 3 Developed with the Matlab R2006a version 7 2 0 232 2 0 0 O0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 9 0 00 0 RE USE SUR DR D PR DURS D SE A SRE DR ES SRE SRE RE ER SE SANS I SR A SRE ee I RE RU ES D SE oe II I NOTE If you want to use your own 2D range image describing your target store your 2D range image typically 500x500 in the folder Images The format of that image MUST be bmp xxx display the list of personal 2D range images To do so select the entry perso al images list in the pop up menu corresponding to the AO AO AN 00 looking angle parameter BEEEEEEEEEEEEEEEEEEEEEEEEECEEEEEEEEEEEEEEEEEEEESESS E f Copyright 2006 2007 Eri B1 Eric anquer oe oe oe oe oe oe oe N N N C oe N N N N N N N N N oO N N N N N N N C N N oe N N N N N C N N N oe N N C N N N C oe
54. r II radars used electromagnetic radiation with radio frequency x 101 Hz to detect remote objects Since that time this technique has been improved and applied to higher and higher frequencies until it reached the optical domain x 10 Hz The LADARs laser detection and ranging or laser radars detect targets using a laser source to produce the electromagnetic radiations The prevalent method is to send a pulse and measure its time of flight when it arrives back at the receiver The measured time gives an estimation of the target range for each laser shot Such LADAR systems provide distance images and could be used as target seekers when mounted on board of missiles of type LOCAAS or E COM The design of such systems implies taking into account numerous parameters and answering many questions One may for example be interested in the flight altitude the laser beam size the range accuracy the pulse repetition frequency or the receiver s properties It is only possible to study independently a few of these parameters Indeed most of them are interconnected making the work complicated and fastidious Thus a simulation is the appropriate means to handle these com plexities and might be of help in future systems designs However such a wide simulator covering all the phenomena from the laser source to the receiver does not exist 1 2 Objectives To tackle this lack a simulator which permits the user to tune numerous pa
55. rameters and then be able to see their different influences is built However this simulator being the first to be developed it has to be concise and focus on the main effects and parameters The purpose of this master s thesis is to develop a simulation model that will be used in LADAR systems design to carry out studies about the influences of the main parameters At the same time a graphical user interface will be added to the 3 4 CHAPTER 1 INTRODUCTION simulation to facilitate its use The final outcome will then be a LADAR simulator 1 3 Thesis Outline The master s thesis is made up of three parts The first one covers the background about lasers and LADARs It includes an introduction and the laser theory used in the simulation The second part focuses on the main concepts of the simulation implementation and gives a description of the graphical user interface Part 3 concludes the report by presenting the possibilities of the simulator and by showing a collection of selected results Finally some discussions about the conclusions and future ideas for extensions of this work are exposed Chapter 2 Laser Beam Propagation Theory In order to understand the work contained in this master s thesis the reader should be familiar with laser This chapter describes the main aspects of laser theory and more particularly its application in LADAR systems The process is subdivided in four parts as shown in Figure 2 1 taken
56. range z R and then D arctan z under the assumption that R gt gt x it yields 9 SL R 3 R u Hence the Equation 2 4 can be rewritten as I x y R Io exp a E A ER Y 2 5 2 2 ENERGY DISTRIBUTION SPACE AND TIME 9 where x y are the cross range dimensions at a distance z R To complete the model the values Gy 1 and Gy 5 have been used in Equation 2 5 and this leads to the expression used in the LADAR simulation I x y R Ip exp 2 a y E E 2 6 or equivalently Ce ien e 0 2 7 5 lt SS 3 SS SSS aS 3 SSS lt SS gS Sn gt Sg gt rf nn DD gt gt gt gt gt gt gt SS n SSS SSS SS SSS SS gt gt gt lt lt l l gt SSS SSS gt gt gt gt Li ES S EX gt gt S gt AAA EA ge 7 gt SS gt gt gt gt gt A AA SS SSS SSS SI SS EA SS gt gt gt EZ gt gt i SSO D S N S ze gt en ren e Figure 2 4 Normalized irradiance at a distance of 50 m F
57. re 2 3 Moreover this figure shows also the function I r of Equation 2 3 The Source Diode Model The dimensions of the emitting area of the semi conductor laser diode are so that its length is 100 times bigger than its width typically 200 umx 2 um Consequently the output aperture is not circular anymore and the model has to be adapted The LADAR simulation is based on the model taken from 6 and is called the source diode model HORS ENT a 2 2 4 Ar Ay where a is the xz divergence angle half divergence angle in the xz plan Gx is the super Gaussian factor for the x direction and has to be greater than 1 0 Similar definitions apply for the y subscripted values Note that the typical Gaussian distribution is obtained when Gr Gy 1 0 An example of profile is given Figure 2 4 Most laser diode manufacturers specify the far field divergence angles as the full width of the distribution between the half power points Orywu4m In order to use the right coefficient a one may apply the following conversion Qi 0 8493218 OrwHM i It is well known that the laser light is highly directional However due to the divergence angles the laser footprint will not have the same size at any range from the laser source It depends on the distance increasing the distance will increase its size Consequently it is sometimes handier to rewrite Equation 2 4 using the following in Figure 3 5 one sees that at target
58. rints are joint and do not overlap They cover perfectly all the original scenery The resulting visualization panel in the ideal case is shown by Figure 4 6 4 2 VISUALIZATION PANEL 37 a Absolute range error Im image to be scanned range image Scanned image range mage lt MSE gt 0919 Im Figure 4 6 Simulation ideal case Zig Zag Scanning The Zig Zag scanning simulation is directly linked to the ZZ SCANNING parameters group of the front panel Section 4 1 1 As shown in Section 3 4 the Z shaped pattern depends simultaneously on several parameters PRF fs V It can happen that the footprints overlap each other if the laser beam has not moved enough in between two laser shots The same portion of scenery is scanned twice To avoid a loss in time efficiency and to improve the robustness with respect to the noise the average of the two overlapping areas is computed The resulting visualization panel of the Zig Zag scanning is shown by Figure 4 7 where the characteristic Z shaped pattern is observed in the middle picture a Absolute range error Im Image to be scanned range image Scanned image range mag P FT LLLLLLLL e LITT TT 2 2 69 all A by 4 0 Figure 4 7 Simulation Zig Zag scanning 38 CHAPTER 4 GRAPHICAL USER INTERFACE 4 3 Workspace Indications The workspace of Matlab is also used to display information about the simu lation which has been run When the pixel simula
59. round trip time of the pulse Impulse response of the matched filter x 10 Matched filtered signal R 57 5602 Time s 10 Time s x 10 Figure 4 5 Pixel simulation 2nd row with matched filter 4 2 2 Simulation LADAR Image Generation In this second part describing the visualization panel the LADAR image generation is presented The range image of the target selected in the target pop up menu is displayed on the first graph The second graph shows the LADAR image generated through the simulation program These two pictures are range images and the corresponding scale is located on the left side of the visualization panel On the other hand the third and last picture represents the absolute range error between the original target and the LADAR image It reveals the error see Section 4 3 for explanations on the error computations between the two images and the related scale is located on its right side Ideal Case The Figure 3 4 page 25 shows that in reality the LADAR picture will be discontinuous because of the scan method That is to say the resulting pic ture will contain pixels only along the Z shaped pattern as seen in the central illustration of Figure 4 7 In the ideal case this difficulty is skipped and con tinuous LADAR images are generated This approximation can be interpreted as a LADAR system using a receiver made of one line of detector cells and flying at an appropriate speed Consequently all the footp
60. s O fwhm x 0 fwhm y divergence angles 3 4 AIRBORNE LASER SCANNING 25 Xacross U J along Xalong Figure 3 4 Z shaped laser scan Laser source Figure 3 5 Laser footprint 26 CHAPTER 3 SIMULATION R target range h flight altitude forward looking angle To make things handier in the image generation it is better to handle pixels with a square shape Since ly and l are different the resulting footprint is rectangle as seen in Figure 3 5 To tackle this problem the value defined as the maximum of ly and ly is used to create a square footprint I max l ly Taking the longest dimension prevents from truncating too drastically the beam profile This results in a beam profile similar to the one shown in Figure 2 4 page 9 The two flat parts surrounding the beam profile are neglected in the computations in order to save time Moreover an extra constraint is added on the divergence angles fwnpm and Orwhm y O the source diode model described in Section 2 2 1 They cannot be chosen freely and are linked by the relation 1 O fwhm x 10 x oh 3 1 Equation 3 1 shows the direct influence of Ofwhm y On Ofwnmx In the LADAR simulation the user can variate fwhm y Which corresponds to variating the longest dimension of the footprint that is to say Finally the unique characteristic dimension of the footprint is reduced to 2R tan ES LR Rx Ofwhmy 3 2 where all the terms
61. s 6 push buttons and a group of 2 radio buttons The latter permits to select the simulation case to be simulated From top to bottom the Close Simu button closes the whole simulation the Help button displays the help file with the descriptions of all simulation controls the RUN LADAR image runs the simulation case indicated by the active radio button the pixel simulation button displays the plots related to one single laser shot one pixel the STOP button breaks the running simulation and finally the Reset Simu closes and re opens the GUI with the default parameters values 4 2 Visualization Panel The visualization panel is the window located in the bottom half of the computer s screen after running the simulation file see Figure 4 1 It shows the results of the simulations LADAR image and pixel simulation ran by the user 4 2 VISUALIZATION PANEL 39 4 2 1 Pixel Simulation The pixel simulation does not generate images but signals plots It corresponds to one single laser shot done to detect the distance of one surface element pixel located at target range Once the pixel simulation has been run an array of 4 graphs are displayed in the visualization panel The first row always provides the same information that is to say a graph with the plot of the laser pulse sent and a graph with three other plots related to the received signal received pulse noisy received pulse and sampled noisy received pulse an example is given in Fi
62. ser physics and technology www rp photonics com PH Accetta and Shumaker The infrared and electro optical systems handbook Vol 6 Active electro optical systems ISBN 0 8194 1072 1 1993 11 O Steinvall Theory for laser systems performance modelling FOA R 97 00599 612 SE SE 1997 112 R Telgarsky M C Cates C Thompson and J N Sanders Reed High fidelity LADAR simulation SPIE 5412 2004 99 54 REFERENCES 13 W J Smith Modern optical engineering the design of optical systems R E Fischer and W J Smith 1990 114 A V Jelalian Laser radar systems Artech house 1992 115 E P Baltsavias Airborne laser scanning basic relations and formulas ISPRS Journal of Photogrammetry and Remote Sensing 54 p199 214 1999 16 O Steinvall D Letalick U S derman L Ulander and A Gustavsson Laser radar for terrain and vegetation mapping FOI R 0232 SE 2001 17 P Andersson Automatic target recognition from laser radar data FOI R 0829 5E 2003 18 A Persson Extraction of individual trees using laser radar data FOI R 0236 SE 2001 19 O Steinvall T Carlsson C Gr nwall H Larsson P Anderson and L Klas n Laser based 3D imaging new capabilities for optical sensing FOI R 0856 SE 2003 Appendix A Parameter Description The following figures numbers A 1 A 2 A 3 A 4 and A 5 contain the m file displayed after pressing the help button on the GUI This file stands for a help file giving brief ex
63. sition e _ target reflectivity Platform Speed traveled distance altitude looking angle pulse repetition frequency scanning Model frequency field of view Source Pulse shape spatial distribution pulse width Model _ pulse power divergence Propagation and reflection LADAR range equation impulse response and convolution reflected waveform atmospheric Model _ attenuation Receiver _ Receiver aperture system efficiency sampling Model M frequency noise level bandwidth Signal and image processing Pulse detection algorithm range computation __ Model _ LADAR image generation Target features extraction Error measurements comparison and Model _ discrimination Figure 3 1 Main simulation processing modules 3 3 SIMULATION STEPS PROCEDURE 21 Nevertheless it is also interesting to see the repartition of the modules related to the process decomposition as shown in Figure 3 2 The laser on board a platform is described by the platform model and the source model The propagation in the atmosphere has been merged with the reflection since it is only an atten uation coefficient which does not required a full module The target interactions are handled by the propagation and reflection model and the target model Finally the receiver stage consists of the receiver model the signal and image processing model and the target features extraction model Platform Model Source Model
64. sponds to the forward looking angle which can be modified only by choosing predefined values These values are stored in the corresponding pop up menu instead of an edit element Line 7 is only a text element standing for an indicator of the distance to the target The value is actualized in function of the user s choices As one notes in the Figure 4 2 the parameters are gathered within four distinct sections detailed in the following la description of all the parameters contained in the front panel is found in the appendix A 4 1 FRONT PANEL 33 ashen poet Laser Pulse Fran ne 100 r P dse power W Se 007 l creer grene angir deg 02 LASER BEAM ar 4 aap aitude m D y locking_enaje _deg 6 al I J f ideal case Re 57 555 2 Zn a4 O Dy Ing scanning system olicency 08 E RUN LADAR image target reflectivdy 01 j f i ATTEMUATIONS tr 4 tmosphorie attenuates 001 i N PAE 905 0 AA A A 0 0 5 1 15 2 25 3 35 4 pisei yes Beton PRF Ju 1000 Time s 10 tac Hr p Y pu 100 122 SCAMIING Fipe distance m Enns u FOV deg 5 oR 100000 FO nse 11 j 40 OPTIONS a m 30 20 range images Target 60 borimo Y Ltrey 60 boxbre v Raval Sima Figure 4 2 Front panel Laser Beam It contains 6 1 elements related to the laser pulse source model These elements are the pulse shape pulse shape the full width at half the maximum of the pulse FWHM the pulse power pulse power one of the t
65. ta syst eta syst is the eificieney of the whole system The value is in the interval 0 1 units XXX target reflectivity rho edit set rho rho is the hemispherical reflectivity of the target and represents the percentage of reflected laser light The value is HP WP oP in the interval 0 1 units XXX V V edit set V V is the speed of the platform in the air and is taken o e into account in the Zig Zag scanning units m s S Push buttons RUN_LADAR image run button je desactivate the main figure start the RUNNING mode clear the second figure run the simulation case selected pixel simulation button o desactivate the main figure start the RUNNING mode run the pixel simulation It simulates the signals obtained for one laser o o shot for one pixel located a the ground distance STOP stop button stop the on going simulation and display a stop message on the workspace Close simu close button Q close the simulation Figure A 4 Help file 4 5 60 APPENDIX A PARAMETER DESCRIPTION Reset simu reset button close and open again the simulation with the default parameters Help button display the help file of the GUI Simulation case selcbk buttongroup oe select the case to be simulated The user can choose between 1 Ideal cases y se and PRF are NOT taken into account in this Simulation It is an ideal case where the
66. that I would never thank enough for his indirect contribution 6 2 SUGGESTED FUTURE WORK 49 6 2 Suggested Future Work The completed work represents the first step in the direction of a thoroughgo ing simulator Hence every stage of the simulation could undergo optimiza tions which would make it closer to the reality and improve its accuracy Above all the LADAR simulation would required detailed validations of the provided information Quantitatively the entire simulation could be sub ject to extensive verifications under predetermined conditions Qualitatively the simulation results may for example be compared with laboratory tests using real devices and targets Afterwards every module could be improved by complexifying the models used The simple atmospheric attenuation coefficient may be substituted by an advanced modelling of the atmospheric effects beam broadening intensity fluctuations and aerosol attenuation The references 7 10 11 provide detailed theory about atmosphere modelling The reflection on the target may for example be developed by taking into account the bidirectional reflection density function BRDF The BRDF describes how the reflected beam spreads into different angles in relation with the surface s properties This gives a more realistic representation of the phenomenon as seen in 1 7 8 As a consequence the target modelling would include more information than the one already contained
67. tion is run the user finds the distance computed The result should be compared with the target range the closer to the target range the result is the more accurate it is When the LADAR image generation has been run indications about res olutions are given footprint size subareas size Moreover two mean square errors MSE are computed 1 The auto mean square error represents the error between the LADAR image generated and the original 2D range image of the target it is the error displayed in figures 4 6 and 4 7 This is the reference error related to the target itself 2 The cross mean square error represents the error between the LADAR image generated and the 2D range image chosen in the library as de tailed in Section 4 1 2 The library contains 2D range images of several targets including the target being scanned The cross mean square error is computed using one of these images Note that if the 2D range image of the target being scanned is selected the result is the same as the one obtained with the auto mean square error Comparing the auto mean square error to the cross mean square error is a first means to identify the similitudes between two objects Working with a not too high noise level one expects the relation auto mean square error lt cross mean square error Equality occurs when the target selected in the library is the same than the
68. wo divergence angle seen in Section 3 4 1 divergence angle the altitude at which the platform is flying altitude and the forward looking angle of the laser beam looking angle The last one is an indicator displaying the distance from the laser source to the target R target Attenuations This group gathers 4 parameters which have a direct influence on the received power the system efficiency the target reflectivity the atmospheric attenuation and the receiver aperture Their influence can be interpreted as a scaling in amplitude of the received signal ZZ Scanning This part is related to the Zig Zag scanning simulation case These parameters are dedicated to this simulation case and describe the flight and scanning characteristics They are the pulse repetition frequency PRF the scan frequency fse the speed of the platform V the distance covered during the flight Flight distance and the field of view of the scanner FOV Options The 1st line allows to choose the number of subareas within the footprint nsa as stated in Section 3 1 more subareas give better precision but required a longer computational time The 2nd and last line of the column disables the detection of 34 CHAPTER 4 GRAPHICAL USER INTERFACE objects located in between the laser source and a distance set up in the edit element ceil range 4 1 2 Front Panel Central Elements In the centre of the front panel seen in Figur
69. y and Range Accuracy 5 0 Zig Zag Scanning 5 4 4 42484 Este eb ads 920 CCONCIMSION 4 242 4 4 6 4434 4 64044 a E a aAA 6 Reflections 6 1 Conclusions 6 2 Suggested Future Work References A Parameter Description B Creation of the source diode model m file C Pulse detection the CFD algorithm m file Index CONTENTS 39 Al Bs ty Hf oO Ge eh i Al er 42 ee ta ee 43 o e a 43 eh Bu 44 La oe ae 45 47 ee HIER 47 HU NUE 49 93 55 61 65 69 List of Figures Za 22 2 3 2 4 2 9 2 6 21 3 1 3 2 3 3 3 4 3 0 3 6 3 7 3 8 4 1 4 2 4 3 4 4 4 5 4 6 4 7 9 1 9 2 9 9 9 4 9 0 6 1 A 1 Process decomposition 5 4 8a Se eee a as Bee 5 Laser range finding principle 6 N Gaussian beam 4 3 amp a ma iaa 7 Normalized irradiance at a distance of 50m 9 Normalized laser pulses with 7a 100 ns 10 Squared attenuation factor ES with 0 01 eee de 12 Range image of a tank T80 13 Main simulation processing modules 20 Modules repartition vaa a 21 SmUlat On principles o gt A wow a eee Boe hes a 24 7 shaped laser scan 4 2 4 4 4 wa owe Mod be we oo OE Sole ES ES 25 Laser OL D 2 4 soni 6 2 oe e OR Se A BS S S Se 25 CED peak detection 4 202 2 Ce eS eh ee PES Re ee 29 Cl Deand CED 50 va oe PEN dG Boe sa i

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