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PF-ASAR Burst-Mode processing Introduction

PF-ASAR Burst-Mode processing Introduction. Algorithms Descalloping options Beam Merging Algorithm APS processing AP channel miss-alignment at SWST changes Conclusions. Betlem Rosich ESA-ESRIN. PF-ASAR Burst-Mode Processing Algorithms.

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PF-ASAR Burst-Mode processing Introduction

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  1. PF-ASAR Burst-Mode processing Introduction • Algorithms • Descalloping options • Beam Merging Algorithm • APS processing • AP channel miss-alignment at SWST changes • Conclusions Betlem Rosich ESA-ESRIN

  2. PF-ASAR Burst-Mode Processing Algorithms • ScanSAR data is characterized by a discontinuous azimuth spectrum. • Specan algorithm has been selected for processing APP/APG, APM, WSM, GMM • IMM products are also processed with Specan, because of higher computation efficiency. • APS products are processed use a single IFFT modified RD algorithm. The processed bandwidth is adjusted to be always 4 times the burst bandwidth. • ScanSAR data is affected by scalloping due to its bursty nature. Descalloping functions are applied during the processing.

  3. SS1 INV. INV.C No desc. WSM descalloping in PF-ASAR • Descalloping options in PF-ASAR for WSM data: • 1. Initial settings: Use of the inverse of the azimuth antenna pattern • Use a flat azimuth pattern (i.e. no descalloping applied)

  4. WSM descalloping in PF-ASAR – SS1 example

  5. FLAT INV. INV.C WSM descalloping in PF-ASAR – SS5 example SS5

  6. WSM descalloping in PF-ASAR - Conclusion Current settings: No descalloping applied • Less sensitivity to Doppler errors: • due to Doppler offsets beam to beam • due to mixture of wind/sea-currents Doppler • Very sligth loss of ENL compard with the use of optimum antenna patterns

  7. APP descalloping in PF-ASAR • Descalloping options in PF-ASAR for APP data: • Initial settings: Use constant SNR descalloping LUT: • - 2 looks case functions used • - the signal and noise in the multilook image are constant in azimuth • - No scalloping visible in any polarisation

  8. Descalloping options in PF-ASAR for APP data: • 2. Use of the inverse of the azimuth antenna pattern • 3. Use a flat azimuth pattern (i.e. no descalloping applied) Current settings: Constant SNR descalloping LUT. Improved azimuth patterns to be used

  9. IMM descalloping in PF-ASAR • Descalloping options in PF-ASAR for IMM data: • Initial settings: Use of the inverse of the azimuth antenna pattern • 2. Use a flat azimuth pattern (i.e. no descalloping applied)

  10. INV. INV.C. IMM descalloping in PF-ASAR (II)

  11. IMM descalloping in PF-ASAR - Conclusion Currrent settings: Inverse of the azimuth antenna Scalloping visible only : - over the sea in case of wind/sea-currents. - anywhere in case Doppler interpolation anomalies occur -> Optimised azimuth antennas to be used

  12. Merging region: N samples Total overlap region Beam Merging Strategy Beam merging: strategy to combine the ScanSAR WSM and GMM independent beam images on the overlapping areas. azimuth range p = 1 linear weighting P = -1 only near beam contributes to the merged one p = 0 only far beam contributes to the merged P = > 1 near beam is favoured

  13. APS Processing Strategy • AP data contains between 2&3 complete burst per aperture and polarization • For APS products: conflict between meeting the standard product quality requirements and ensuring maximum processed bandwidth for InSAR applications • Adopted solution in PF-ASAR: Keep 2 complete looks for all samples • - most of the available bandwidth is kept • - a modulation in the IRF is introduced • - the nominal IRF quality requirements cannot be achieved

  14. APS Processing Strategy (II) • The IRF modulation can be characterized as the coherent addition of 2 sinc(t) functions with frequency shift of twice the burst bandwidth:

  15. APS Processing Strategy (III) • APS IRF requirements modified to accept the introduced modulation:

  16. AP Channel miss-registration • There is systematic a miss-registration between the 2 AP polarizations at every SWST change. • The SWST change is annotated in the data 4 burst before it really occurs. • The processor corrects for a SWST change that has not been applied and introduces a range shift and data defocusing, • The problem will be solved with a patch on the on-board s/w or with a correction in PF-ASAR.

  17. Conclusions • Current optimum descalloping options: Constant SNR for APP and no descalloping for WSM &I MM. • Scalloping improvement expected with final azimuth patterns • No artifacts detected on the beam merging regions. Optimization to be performed. • APS IRF quality requirements modified to accept the IRF modulation due to the RD processing on 2 looks. • Offset between the annotation and the implementation of SWST changes to be handled by the processor or to be modified on board.

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