PF-ASAR Burst-Mode processing
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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

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 introduction

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.


Pf asar burst mode processing introduction

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)


Pf asar burst mode processing introduction

WSM descalloping in PF-ASAR – SS1 example


Pf asar burst mode processing introduction

FLAT

INV.

INV.C

WSM descalloping in PF-ASAR – SS5 example

SS5


Pf asar burst mode processing introduction

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


  • Pf asar burst mode processing introduction

    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


    Pf asar burst mode processing introduction

    • 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


    Pf asar burst mode processing introduction

    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)


    Pf asar burst mode processing introduction

    INV.

    INV.C.

    IMM descalloping in PF-ASAR (II)


    Pf asar burst mode processing introduction

    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


    Pf asar burst mode processing introduction

    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


    Pf asar burst mode processing introduction

    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


    Pf asar burst mode processing introduction

    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:


    Pf asar burst mode processing introduction

    APS Processing Strategy (III)

    • APS IRF requirements modified to accept the introduced modulation:


    Pf asar burst mode processing introduction

    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.


    Pf asar burst mode processing introduction

    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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