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PF-ASAR Burst-Mode processing Introduction

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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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Presentation Transcript
slide1
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

slide2
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.
slide3
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)
slide5
FLAT

INV.

INV.C

WSM descalloping in PF-ASAR – SS5 example

SS5

slide6
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
slide7
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
slide8
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

slide9
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)
slide10
INV.

INV.C.

IMM descalloping in PF-ASAR (II)

slide11
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

slide12
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

slide13
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
slide14
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:
slide15
APS Processing Strategy (III)
  • APS IRF requirements modified to accept the introduced modulation:
slide16
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.
slide17
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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