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

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