Ingo Walterscheid , Thomas Espeter, Jens Klare, Andreas Brenner, Joachim Ender POTENTIAL AND LIMITATIONS OF FORWARD-LOOKIN...
OUTLINE <ul><li>Introduction </li></ul><ul><li>Bistatic forward-looking SAR </li></ul><ul><ul><li>Geometry </li></ul></ul>...
Introduction Monostatic SAR <ul><ul><li>Independent of weather and time of day </li></ul></ul><ul><ul><li>High azimuth res...
Introduction Bistatic SAR <ul><li>Advantages: </li></ul><ul><ul><li>Additional information about the target (bistatic RCS)...
Bistatic forward-looking SAR Geometry and applications <ul><ul><li>Applications: </li></ul></ul><ul><ul><li>Observation, a...
Bistatic forward-looking SAR  Iso-range and iso-Doppler contours (Monostatic case) For monostatic radars it is quite simple:
Bistatic forward-looking SAR  Iso-range and iso-Doppler contours (Monostatic case) Tx/Rx Side-looking Forward-looking
Bistatic forward-looking SAR  Iso-range contours (Bistatic case) <ul><li>Bistatic geometry </li></ul>TX RX R 1 (  ) R 2 (...
Bistatic forward-looking SAR  Iso-range contours (Bistatic case) The set of equal bistatic range is an ellipsoid with its ...
Bistatic forward-looking SAR  Iso-range-rate (Doppler) contours (Bistatic case) <ul><ul><li>Set of equal contribution  v i...
Bistatic forward-looking SAR  Iso-range-rate (Doppler) contours (Bistatic case) <ul><ul><li>Black rings are cuts between t...
Bistatic forward-looking SAR Iso-range and iso-Doppler contours Bistatic geometry Red  = Iso-range lines,  Blue  = Iso-Dop...
Bistatic forward-looking SAR  Resolution in range and cross-range <ul><li>Ground range resolution </li></ul><ul><li>Ground...
Experiment with TerraSAR-X and PAMIR Sensor parameters <ul><li>TerraSAR-X </li></ul><ul><ul><li>X-Band SAR satellite </li>...
Experiment with TerraSAR-X and PAMIR Bistatic configuration <ul><li>TerraSAR-X </li></ul><ul><ul><li>High-resolution spotl...
Experiment with TerraSAR-X and PAMIR Data acquisition <ul><li>Bistatic signal acquisition </li></ul><ul><ul><li>Standard g...
Experiment with TerraSAR-X and PAMIR  Pulse synchronization (I) <ul><li>PRF triggering </li></ul><ul><ul><li>Hardware sync...
Experiment with TerraSAR-X and PAMIR  Pulse synchronization (II) <ul><li>PRF jitter </li></ul><ul><ul><li>Caused by instab...
Experiment with TerraSAR-X and PAMIR  Expected ground range and cross-range resolution  <ul><li>Ground range resolution </...
Experiment with TerraSAR-X and PAMIR  Iso-range and iso-Doppler contours (backward-looking) Tx Rx
Experimental results Raw data and range compressed data Amplitude of raw data Range compressed data
Experimental results Google Earth image of the scene
Experimental results Optical image      Bistatic SAR image
Summary Film
Summary <ul><ul><li>Imaging in forward-looking direction using bistatic SAR </li></ul></ul><ul><ul><li>Bistatic geometry a...
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MO4.L09 - POTENTIAL AND LIMITATIONS OF FORWARD-LOOKING BISTATIC SAR

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MO4.L09 - POTENTIAL AND LIMITATIONS OF FORWARD-LOOKING BISTATIC SAR

  1. 1. Ingo Walterscheid , Thomas Espeter, Jens Klare, Andreas Brenner, Joachim Ender POTENTIAL AND LIMITATIONS OF FORWARD-LOOKING BISTATIC SAR TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: A A A A A A A
  2. 2. OUTLINE <ul><li>Introduction </li></ul><ul><li>Bistatic forward-looking SAR </li></ul><ul><ul><li>Geometry </li></ul></ul><ul><ul><li>Iso-range and Iso-Doppler contours </li></ul></ul><ul><ul><li>Resolution </li></ul></ul><ul><li>Experiment with TerraSAR-X and PAMIR </li></ul><ul><li>Experimental results </li></ul><ul><li>Summary </li></ul>
  3. 3. Introduction Monostatic SAR <ul><ul><li>Independent of weather and time of day </li></ul></ul><ul><ul><li>High azimuth resolution </li></ul></ul><ul><ul><li>Widely used for surveillance and remote sensing applications </li></ul></ul>Monostatic synthetic aperture radar typically operates with a side-looking antenna to obtain high resolution images <ul><li>Solutions using one radar platform: </li></ul><ul><ul><li>Doppler beam sharpening using a rotating reflector antenna </li></ul></ul><ul><ul><li>Linear array antenna with one Tx and multiple Rx antennas </li></ul></ul><ul><ul><li>Limitation: </li></ul></ul><ul><ul><li>Imaging in forward- and backward-looking direction </li></ul></ul><ul><ul><ul><li>Left/right ambiguities </li></ul></ul></ul><ul><ul><ul><li>Poor Doppler resolution </li></ul></ul></ul>
  4. 4. Introduction Bistatic SAR <ul><li>Advantages: </li></ul><ul><ul><li>Additional information about the target (bistatic RCS) </li></ul></ul><ul><ul><li>Reduction of dynamic range (di- and polyhedral effects in urban areas) </li></ul></ul><ul><ul><li>Single-track interferometry with large baselines (across- and along-track) </li></ul></ul><ul><ul><li>Coherent and incoherent combination of bi- and monostatic signatures </li></ul></ul><ul><ul><li>Reduction of vulnerability in military systems </li></ul></ul><ul><ul><li>Imaging in flight direction or backwards </li></ul></ul>Bistatic synthetic aperture radar operates with spatially separated transmit and receive antennas that are mounted on separated platforms
  5. 5. Bistatic forward-looking SAR Geometry and applications <ul><ul><li>Applications: </li></ul></ul><ul><ul><li>Observation, autonomous navigation </li></ul></ul><ul><ul><li>Landing assistance under low-visibility conditions (flight safety) </li></ul></ul><ul><ul><li>Identification of obstacles in flight direction (collision warning system) </li></ul></ul><ul><ul><li>Compact, low-cost and lightweight receive-only radar imaging system for small aircrafts </li></ul></ul><ul><ul><li>Geometry: </li></ul></ul><ul><ul><li>Platform velocities v 1 and v 2 </li></ul></ul><ul><ul><li>LOS vectors u 1 and u 2 </li></ul></ul>
  6. 6. Bistatic forward-looking SAR Iso-range and iso-Doppler contours (Monostatic case) For monostatic radars it is quite simple:
  7. 7. Bistatic forward-looking SAR Iso-range and iso-Doppler contours (Monostatic case) Tx/Rx Side-looking Forward-looking
  8. 8. Bistatic forward-looking SAR Iso-range contours (Bistatic case) <ul><li>Bistatic geometry </li></ul>TX RX R 1 (  ) R 2 (  ) r Bistatic range history Sum of two hyperbolas!
  9. 9. Bistatic forward-looking SAR Iso-range contours (Bistatic case) The set of equal bistatic range is an ellipsoid with its focus points at Tx and Rx (Iso-range surface). The cut with the earth surface is an ellipse (Iso-range-line).
  10. 10. Bistatic forward-looking SAR Iso-range-rate (Doppler) contours (Bistatic case) <ul><ul><li>Set of equal contribution v i is a cone surface with axis = flight direction and corner at platform </li></ul></ul><ul><ul><li>Iso-range-rate surface is the union over all cuts between the cones with the same sum of radial velocities </li></ul></ul><ul><ul><li>Radial velocities </li></ul></ul>
  11. 11. Bistatic forward-looking SAR Iso-range-rate (Doppler) contours (Bistatic case) <ul><ul><li>Black rings are cuts between the range-rate cones </li></ul></ul><ul><ul><li>Union of these rings for equal range-rate sum form the Iso-range-rate surface </li></ul></ul><ul><ul><li>Cut of this surface with the earth surface forms the Iso-range-rate contours </li></ul></ul>
  12. 12. Bistatic forward-looking SAR Iso-range and iso-Doppler contours Bistatic geometry Red = Iso-range lines, Blue = Iso-Doppler lines Non degenerated image grid in flight direction Rx Tx Monostatic geometry Tx/Rx
  13. 13. Bistatic forward-looking SAR Resolution in range and cross-range <ul><li>Ground range resolution </li></ul><ul><li>Ground Doppler resolution </li></ul>Ground cross-range resolution c,  Velocity of light, wavelength B Signal bandwidth u i Unit direction vector (LOS)  xy Projector onto x-y-plane T int Integration time  i Angular speed vector  Angle between gradient of iso-range and iso-Doppler lines  with
  14. 14. Experiment with TerraSAR-X and PAMIR Sensor parameters <ul><li>TerraSAR-X </li></ul><ul><ul><li>X-Band SAR satellite </li></ul></ul><ul><ul><li>Centre frequency: 9.65 GHz </li></ul></ul><ul><ul><li>Bandwidth: 300 MHz </li></ul></ul><ul><ul><li>Active phased array antenna </li></ul></ul><ul><ul><li>Azimuth scan range: +/- 0.75° </li></ul></ul><ul><ul><li>Altitude: 515 km </li></ul></ul><ul><ul><li>Velocity: 7600 m/s </li></ul></ul><ul><li>PAMIR </li></ul><ul><ul><li>SAR/GMTI System, Transall C-160 </li></ul></ul><ul><ul><li>Centre frequency: 9.45 GHz </li></ul></ul><ul><ul><li>Bandwidth: 1820 MHz </li></ul></ul><ul><ul><li>Active phased array antenna </li></ul></ul><ul><ul><li>Azimuth scan range: +/- 45° </li></ul></ul><ul><ul><li>Altitude: 0.6 – 4 km </li></ul></ul><ul><ul><li>Velocity: 100 m/s </li></ul></ul>
  15. 15. Experiment with TerraSAR-X and PAMIR Bistatic configuration <ul><li>TerraSAR-X </li></ul><ul><ul><li>High-resolution spotlight mode (right-side looking) </li></ul></ul><ul><ul><li>Incidence angle: 24° </li></ul></ul><ul><ul><li>PRF ≈ 4.5 kHz </li></ul></ul><ul><ul><li>Altitude: 515 km </li></ul></ul><ul><ul><li>Velocity: 7600 m/s </li></ul></ul><ul><li>PAMIR </li></ul><ul><ul><li>Flight direction orthogonal to TerraSAR-X trajectory </li></ul></ul><ul><ul><li>Stripmap (backward-looking) </li></ul></ul><ul><ul><li>Incidence angle: 60° </li></ul></ul><ul><ul><li>PRF ≈ 1.5 kHz </li></ul></ul><ul><ul><li>Altitude: 1500 m </li></ul></ul><ul><ul><li>Velocity: 100 m/s </li></ul></ul>
  16. 16. Experiment with TerraSAR-X and PAMIR Data acquisition <ul><li>Bistatic signal acquisition </li></ul><ul><ul><li>Standard gain horn on the aircraft‘s loading ramp </li></ul></ul><ul><ul><li>Azimuth/Elevation beamwidth of 27° </li></ul></ul><ul><ul><li>PRF RX = PRF TX /3 </li></ul></ul><ul><li>Direct signal acquisition </li></ul><ul><ul><li>Receiving of direct signal for synchronization purposes </li></ul></ul><ul><ul><li>Additional antenna on the top of aircraft‘s fuselage </li></ul></ul>
  17. 17. Experiment with TerraSAR-X and PAMIR Pulse synchronization (I) <ul><li>PRF triggering </li></ul><ul><ul><li>Hardware synchronization </li></ul></ul><ul><ul><ul><li>Pulsed acquisition mode </li></ul></ul></ul><ul><ul><ul><li>Direct signal </li></ul></ul></ul><ul><ul><ul><li>Timing controller of PAMIR is triggered </li></ul></ul></ul><ul><ul><li>Software synchronization </li></ul></ul><ul><ul><ul><li>Remaining shift of subsequent rangelines </li></ul></ul></ul><ul><ul><ul><li>Compensation during a pre-processing step </li></ul></ul></ul>
  18. 18. Experiment with TerraSAR-X and PAMIR Pulse synchronization (II) <ul><li>PRF jitter </li></ul><ul><ul><li>Caused by instabilities of the oscillators and the recording system </li></ul></ul><ul><ul><li>Quantified by RMS </li></ul></ul><ul><ul><li>Impact on focusing quality: </li></ul></ul><ul><ul><li>Range imaging </li></ul></ul><ul><ul><ul><li>Range bin >> c  max(  t)  No impact </li></ul></ul></ul><ul><ul><li>Azimuth imaging </li></ul></ul><ul><ul><ul><li>Coherence limitation Á err < ¼ /4 </li></ul></ul></ul><ul><ul><ul><li>Max. phase error Á err = ! 0 (4 ¾ )  ¾ < 3.24 ps </li></ul></ul></ul><ul><ul><ul><li>Compensation is required </li></ul></ul></ul>Measured timing jitter generated by the recording system (RMS = 86.95 ps)  t 1  t 2  t 3 Ideal PRF
  19. 19. Experiment with TerraSAR-X and PAMIR Expected ground range and cross-range resolution <ul><li>Ground range resolution </li></ul><ul><li>Cross-range resolution </li></ul>
  20. 20. Experiment with TerraSAR-X and PAMIR Iso-range and iso-Doppler contours (backward-looking) Tx Rx
  21. 21. Experimental results Raw data and range compressed data Amplitude of raw data Range compressed data
  22. 22. Experimental results Google Earth image of the scene
  23. 23. Experimental results Optical image  Bistatic SAR image
  24. 24. Summary Film
  25. 25. Summary <ul><ul><li>Imaging in forward-looking direction using bistatic SAR </li></ul></ul><ul><ul><li>Bistatic geometry and resolution </li></ul></ul><ul><ul><li>Iso-range and iso-range-rate contours in the bistatic case </li></ul></ul><ul><ul><li>Bistatic experiment with TerraSAR-X and PAMIR to demonstrate the feasibility to image in forward and backward direction </li></ul></ul><ul><ul><li>Experimental results </li></ul></ul>
  26. 26. Thank you very much!

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