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Alternating Polarization ´Single´ Look Complex Product Status

Alternating Polarization ´Single´ Look Complex Product Status. Nominal Product Characteristics Impulse Response Measurements Ambiguity Measurements Noise Equivalent RCS Scalloping Measurements Localization Accuracy Conclusions. Josep Closa ESA-ESRIN. APS Product Characteristics.

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Alternating Polarization ´Single´ Look Complex Product Status

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  1. Alternating Polarization ´Single´ Look Complex Product Status • Nominal Product Characteristics • Impulse Response Measurements • Ambiguity Measurements • Noise Equivalent RCS • Scalloping Measurements • Localization Accuracy • Conclusions Josep Closa ESA-ESRIN ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  2. APS Product Characteristics • Slant range complex products • One product contains two images in two possible polarization combinations: HH-VV HH-HV VV-VH • Elevation antenna pattern and range spreading loss corrections are not applied during processing • Product size of up to 1.2 Gbytes: 4 bytes per complex sample (2I + 2Q) • Swath widths of 100 km (IS1) to 56 km (IS7) with azimuth extents of ~100 km • Range resolution fixed to ~ 8.3 m (16 MHz chirp bandwidth used for all swaths) • Natural pixel spacing (sampling frequency and PRF) ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  3. APS Product Characteristics • Products processed with the modified range-Doppler phase preserving algorithm • Total azimuth bandwidth is kept to 4 looks (2 azimuth looks per image) • Azimuth resolution depends on number of pulses per burst + modulation of the IRF due to scansar acquisition ~ 6.7 m • Doppler is estimated using data from both polarization and the same valued is used to process both images • No window is applied during range processing • Inverse of the azimuth antenna pattern is applied to the azimuth spectrum to descallop the images • Range compression performed with nominal chirp • Image normalization performed using constant reference values due to AP calibration pulse corruption ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  4. APS Product Examples ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 HH and HV Polarization image orbit 3579 VV and VH Polarization image orbit 3712

  5. APS Product Examples ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  6. Ceos Offset Test • Ceos Offset Test performed on orbit 3579 over Resolute Bay (HV polarization) introducing a shift of 200 samples in range and azimuth • Mean Phase difference: 0.006651degrees. Mean absolute difference: 0.089921degrees Std. Dev: 0.928326 (requirements mean <0.1, stdev <5.5) • No artefact detected in range. Azimuth processing blocks visible ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  7. IRF Analysis • Analysis based on acquisitions over ESA transponders • First analysis on the optimization of product digital values dynamic range • I/Q peak values below optimum value • Amplitude statistics on backscatter Edam in VV polarization orbit 3712 - IS2 Processing Gain too low ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  8. IRF Function • Response is visible in both polarization images • Modulation in the azimuth response Azimuth Resolution on modulated response: 5.6 m Azimuth resolution on envelope: 27.6 m Range Resolution: 8.35 m ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  9. Interpolated IRF function Edam VV resampled Orbit 3712 - IS2 ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  10. Range and Azimuth Resolution Range resolution • Range and azimuth resolution within requirements for most cases (theoretical value ± 10%) • Range resolution: 8.35 ± 0.1 m • Azimuth resolution: 6.11 ± 0.5 m • Additional modulation detected on some azimuth responses Azimuth resolution Theoretical range resolution: 8.31 m ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  11. Strange azimuth responses ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  12. Range and Azimuth PSLR • Range and azimuth PSLR within requirements (theoretical value 5 dB!!) • Low azimuth PSLR values detected on the degradated azimuth IRF Theoretical range PSLR: -13.3 dB Theoretical azimuth PSLR: -3.5 dB Mean: 12.86 dB Stdev: 0.2 Mean: -3.28 dB Stdev: 0.3 Azimuth PSLR Range PSLR ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  13. ISLR and Spurious Sidelobe Levels • ISLR values slightly different from requirements (-0.64 dB) except for the cases with degradated azimuth IRF • Spurious SLR significantly different from requirements (-25 dB) Mean: -15.6 dB Mean: +1.45 dB Spurious Sidelobe Levels ISLR ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  14. Azimuth Ambiguities • Azimuth ambiguities from the transponder response can be observed on Edam, Swifterband and Aalsmeer transponders • Results in the range of -31.0dB to -23.12 dB • Average PT azimuth ambiguity ratio: -27.9 dB < Requirement: –25 dB Edam ambiguity response 3828 IS4 HV ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  15. Calibration Constant and Radiometric Stability • Very few measurements to derive calibration constant • Different calibration constants per beam to be compensated with updated nominal reference energy values • High stability within the beam • Almost no variation with polarization ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  16. Cross- Talk • Transponder response cal always be detected on both polarization images • High variation of peak to peak intensity difference Peak Intensity Differences Edam HV on the resampled image ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  17. Noise Equivalent RCS • Azimuth modulation similar to scalloping detected on the cross-polar images for ALL the acquisitions • Effect due to the descalloping function applied on thermal noise • Noise measured on the sea areas (using previous calibration constants) for all the beams agrees with predicted estimates ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  18. Scalloping • Scalloping detected only on one image and over the sea area • Scalloping visible on both polarization images • Radiometric error due to scalloping 0.2 dB on both images ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  19. Localization Accuracy / Channel co-registration • Localization accuracy derived from the difference between the estimated transponder position and the detected one • Cross-talk on the transponders allows to give an estimate of the co-registration of the two images. Values within requirements <0.25*pixel ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

  20. Conclusions Modulated azimuth response • APS characterization: two azimuth looks • Internal calibration not used to perform product normalization • Processing gains need to be increased • Transponder responses can be detected on both polarization images • Range and azimuth geometric resolution agree with expected values • ISLR and Spurious Side Lobe Ratio different from expected values • Very few transponder measurements per swath to derive calibration constant • Different calibration constant per swath • NES0 slightly better than predictions • Almost no scalloping. Descalloping function can be detected on noise images • Localization accuracy within 3 pixels except for some outliers • Channel co-registration within requirements ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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