Diese Präsentation wurde erfolgreich gemeldet.
Die SlideShare-Präsentation wird heruntergeladen. ×
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Anzeige
Wird geladen in …3
×

Hier ansehen

1 von 31 Anzeige

Weitere Verwandte Inhalte

Diashows für Sie (20)

Andere mochten auch (19)

Anzeige

Ähnlich wie PresentationSAR (20)

PresentationSAR

  1. 1. Signal Processing of SAR Detection Algorithm
  2. 2. SAR Signal Specifications: The LFM signal equation has same form in spatial and frequency domain. Range frequency in LFM has direct relation with range frequency: f  Kr . t If t change from 0 to T, f change from 0 to BW. f = BW f = 0 Hz t = Tt = 0
  3. 3. SAR Signals: Strip-map mode Moving direction (Nadir line) Delay time in receive signal The plane in moving during send and receive. Doppler effect and plane’s moving makes SAR system complex. Range Cell Migration is to find exact place of the surface where the receive signal hit it and reflect.
  4. 4. SAR Signals and RCM: Complexity hierarchical 1. Line beam, no movement 2. Line beam, with movement 3. Antenna beam, no movement (-) 4. Antenna beam, with movement(+) (-): Pulse-signal SAR (Doppler effect) stop-and-go situation (+): LFM-CW SAR
  5. 5. SAR Processing Algorithms Range Doppler Algorithm Chirp Scaling Algorithm Omega-K Algorithm
  6. 6. SAR Processing Algorithm Send and Received Signals: Signal Bandwidth is defined by pulse duration and Kr parameter. The echo signal multiply by reference signal and digitized by ADC. * Redc Transmit ceiveS S S= × rBandWidth K T τ = ×
  7. 7. De-chirp Signal Bandwidth: Frequency Domain: Bandwidth shift by center of image, using Lowpass filter Range bandwidth: Plane height = 1000 m Plane speed = 50 m/s Plane angle = 50 degree Squint angle = 0 Range variations from 1300 to 2000 meter De-chirp Signal Bandwidth is determined by SAR range of detection. The echo signal multiply by reference signal and digitized by ADC. 2 0 0 0 0 0( , , , ) ( , ) exp( 2 )dc r rS t r s r s j f j K j K tτ σ π τ π τ π τ= × ∆ − ∆ + ∆ 2 0 0 0( ) ( , ) exp( 2 ) exp( 2 )dc r rF S r s j f j K j K t j ft dtσ π τ π τ π τ π= × ∆ − ∆ + ∆ × −∫
  8. 8. De-chirp Signal Bandwidth: Range frequency: Bandwidth = 1 MHz Range variations from 1300 to 2000 meter Delay is dictated by slant range: Range frequency spectrum:
  9. 9. Stationary-Phase Principle: POSP is used to approximate Fourier transform in Azimuth direction.
  10. 10. Stationary-Phase Principle: Phase-Stationary to get a mathematical view to Fourier transform of De-chirp signal For example: 2 0 0 0( , ) exp( 2 2 ) exp( 2 ).dc r r sSf r s j f j K j K t j f t dtσ π τ π τ π τ π= × ∆ − ∆ + ∆ × −∫ 2 02 2 2fourier r r s sf K K t f tθ π τ π τ π τ π= ∆ − ∆ + ∆ − 2 2 2 022 sr v tR c c τ + = = ' 0 d dt θ θ = = Phase-Stationary is a place where amplitude variation is ignorable against phase variation. 2 0 0 0 0 0( , , , ) ( , ) exp( 2 )dc r rS t r s r s j f j K j K tτ σ π τ π τ π τ= × ∆ − ∆ + ∆
  11. 11. Taylor approximation used to linear azimuth and range in formula Taylor approximations: Taylor approximations can be used
  12. 12. Taylor approximations: Considering phase of Fourier transform, it composed of three nonlinearity need to be solved before proceeding. The first term is modulation of azimuth , the second is RCM which is linear to range frequency, and the last is secondary range compression. Each part must be compensated to derive a phase in two in-depended dimension. These nonlinearities and dependencies can be solved in frequency domain or by changing the variables and domains. The second is defined as w-k algorithm. In this method the range and azimuth frequency domain change to w-k domain which in the new domain the domains are orthogonal too. In w-k algorithm the Reference Function Multiply is used for decoupling, and created in w-k domain.
  13. 13. Reference Function Multiply Reference function multiply In w-k algorithm Rc is the slant range from plane to center of the target scene Rc is the center of Bandwidth in range’s Fourier transform Reference function multiply change the phase of signal by distance from Rc
  14. 14. Focusing in LFM-CW Omega-K : Returning from w-k domain by inverse Fourier transform: The position of the target appear as a spike function (Delta) in range-azimuth domain. The Phase Stationary algorithm can locate targets by approximation.
  15. 15. Simulation’s parameters and values: The simulations is done in lower sampling frequency, for fast results. Here are the aspects of the simulations: h = 300 m , plane altitude Squint angle from 0 degree to 5 degree v = 50 m/s, speed of the plane fs = 2 Msps , sampling frequency after de-chirping xc = 357 m, angular center of image PRF = 1000 Hz Pulse Duration = 1 ms Carrier frequency = 9.6 GHz Chirp Bandwidth = 200 MHz Xnear and Xfar are 252 and 519 meters respectively. Rnear and Rfar are 391 and 600 meters respectively. Azimuth and range resolutions are 0.2 and 0.75 meters respectively. The signals are generated in Matlab and C, for time saving.
  16. 16. Test Conditions: The test condition change by: Number of targets Position of targets Squint angle Test conditions : 1.One-Target in Middle of image, Squint angle = 0 degree •Two-Target in Xnear and Xfar, Squint angle = 0 degree • one-Target in Corner, Squint angle change from 4.5 to 7.5 degree • Four Targets in corners, (Xnear, Xfar, strip’s width= 10m) • Multi-Target, Squint angle = 0 degree • Multi-Target, Squint angle = 5.3 degree
  17. 17. Test Conditions 1: Target’s location is [Xc,0], Squint angle = 0 PSLR = -13.41 dB Distance from 1th-peak to 2th-peak in azimuth direction is about 4 pixel. Range distinction ability is 1 pixel. Drop in range direction is about 56 dB 460 480 500 520 540 -10 0 10 20 X: 501 Y: 19.33 DetectioninAzimuth-Direction SignalStrength[dB] X: 497 Y: 5.917 X: 505 Y: 5.917 0 500 1000 1500 2000 -100 -50 0 50 DetectioninRange-Direction SignalStrength[dB] 995 1000 1005 1010 -40 -20 0 20
  18. 18. Test Conditions 1: Target’s location is [Xc,0] OutputImage 500 1000 1500 2000 200 400 600 800 1000 500 1000 1500 300 400 500 600 700 800 900 1000 1100 1200 400 450 500 550 600 900 950 1000 1050 1100 450 500 550 940 960 980 1000 1020 1040 1060 480 490 500 510 520 980 990 1000 1010 1020 496 498 500 502 504 506
  19. 19. Test Conditions 1: Target’s detection amplitude Target’s detection amplitude [dB]
  20. 20. Test Conditions 2: Two target at [Xnear,0] , [Xfar,0] Plane’s Height = 300 m Xnear and Xfar (from 40 to 60 degree from Nadir line to Target) equals 252 and 519 meters respectively, so, Rnear and Rfar equals 391 and 600 meters. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 -100 -80 -60 -40 -20 0 20 DetectioninRange-Direction SignalStrength[dB] 900 950 1000 1050 1100 1150 1200 -20 0 20 X: 1179 Y: 16.85 SignalStrength[dB] X: 901 Y: 19.81 DetectioninRange-Direction As show in range detection image, the peaks happened at range indexes 901, 1179. The Range Resolution equals 0.75 meter, and Rc is 466 meter, so, the differences is -75 and 133 for Rnear and Rfar. (75/0.75 = 100, 133/0.75 = 177)
  21. 21. Test Conditions 2: Two target at [Xnear,0] , [Xfar,0]. Azimuth detection: 0 200 400 600 800 1000 -60 -40 -20 0 20 DetectioninAzimuth-Direction SignalStrength[dB] 450 500 550 -10 0 10 20 DetectioninAzimuth-Direction SignalStrength[dB] 480 490 500 510 520 530 -20 -10 0 10 20 DetectioninAzimuth-Direction PSLR = -14.9 dB The second peak happened at 4th pixel away the center.
  22. 22. Test Conditions 2: Two target at [Xnear,0] , [Xfar,0]. Output image is reconstructed as below : 500 1000 1500 2000 200 400 600 800 1000 895 900 905 490 500 510 1160 1165 1170 1175 1180 1185 1190 1195 490 500 510 850 900 950 1000 1050 1100 1150 1200 450 500 550
  23. 23. Test Conditions 3 (squint = 4.5): One target at [Xc,0] , squint angle equals to 4.5 degree. Range’s resolution is 1 pixel, in azimuth direction PSLR=-13.85dB. 920 940 960 980 1000 1020 1040 1060 -20 -10 0 10 20 DetectioninAzimuth-Direction(squint=4.5degree) SignalStrength[dB] 0 500 1000 1500 2000 -80 -60 -40 -20 0 20 DetectioninRange-Direction(squint=4.5degree) SignalStrength[dB] OutputImage 500 1000 1500 2000 200 400 600 800 1000 1200 1400 980 990 1000 1010 1020 980 1000 1020 1040
  24. 24. OutputImage 995 1000 1005 1010 1150 1200 1250 Test Conditions 3 (squint = 7.5): One target at [Xc,0] , squint angle equals to 7.5 degree (half of the data is valid). Range’s resolution is 1 pixel, in azimuth direction PSLR=-12.78dB (in 9 pixel). 1190 1200 1210 1220 1230 1240 -30 -20 -10 0 10 DetectioninAzimuth-Direction(squint=7.5degree) 0 500 1000 1500 2000 -80 -60 -40 -20 0 20 DetectioninRange-Direction(squint=7.5degree) SignalStrength[dB] 1000.5 1001 1001.5 1205 1210 1215 1220
  25. 25. OutputImage 500 1000 1500 2000 200 400 600 800 1000 1200 Test Conditions 3 (squint = 5.3): One target at [Xnear,0] , squint angle equals to 5.3 degree. Range’s resolution is 1 pixel, in azimuth direction PSLR=-13.84dB. Maximum acceptable squint is 5.3 degree. 870 880 890 900 910 920 930 940 980 990 1000 1010 1020 0 500 1000 1500 2000 -80 -60 -40 -20 0 20 DetectioninRange-Direction(squint=5.3degree) SignalStrength[dB] 950 1000 1050 1100 -20 -10 0 10 DetectioninAzimuth-Direction(squint=5.3degree) SignalStrength[dB]
  26. 26. Test Conditions 4: Four-Target in corners, (Xnear, Xfar, strip’s width=10m) The peaks happened at 900 and 1179 in range, 401 and 601 in azimuth direction. Rnear = 391 m Rfar = 600 m Rc = 466 m Range’s resolution = 0.75 m (466 - 391)/0.75 = 100 (600-466)/0.75 = 177 Image boundary is detected. 0 500 1000 1500 2000 -80 -60 -40 -20 0 20 DetectioninRange-Direction SignalStrength[dB] 0 500 1000 1500 -40 -20 0 20 DetectioninAzimuth-Direction SignalStrength[dB]
  27. 27. Test Conditions 4: Four Targets in corners, (Xnear, Xfar, strip’s width=10m) (Image’s corners detection) OutputImage 900 950 1000 1050 1100 1150 400 450 500 550 600
  28. 28. Test Conditions 5: Multi-Target, squint angle = 0 degree White pixels of the image separated by 1 black pixel in azimuth and 2 black pixel in range direction. The white pixels have values. Each pixel width equals 1 meter. Image size is 8 * 28 meters, Image starts from Xc to Xc+28 Range Direction OutputImage 1155 1160 1165 1170 1175 1180 1185 1190 550 600 650
  29. 29. Test Conditions 5: Multi-Target, squint angle = 0 degree 0 200 400 600 800 1000 1200 -40 -20 0 20 DetectioninAzimuth-Direction SignalStrength[dB] 1155 1160 1165 1170 1175 1180 1185 5 10 15 20 DetectioninRange-Direction SignalStrength[dB] 500 550 600 650 0 10 20 DetectioninAzimuth-Direction SignalStrength[dB]
  30. 30. Test Conditions 5 (complex image): Multi-Target, squint angle=0 degree, strip’s width=60 meters, strip’s length= 267 meters Range Direction OutputImage 900 950 1000 1050 1100 1150 1200 200 400 600 800 1000
  31. 31. Thanks for Attention

×