PF-ASAR Burst-Mode processing
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PF-ASAR Burst-Mode processing Introduction PowerPoint PPT Presentation


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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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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

  • 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.


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)


WSM descalloping in PF-ASAR – SS1 example


FLAT

INV.

INV.C

WSM descalloping in PF-ASAR – SS5 example

SS5


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


  • 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


    • 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


    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)


    INV.

    INV.C.

    IMM descalloping in PF-ASAR (II)


    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


    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


    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


    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:


    APS Processing Strategy (III)

    • APS IRF requirements modified to accept the introduced modulation:


    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.


    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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