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

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

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

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

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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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: 0.006651 degrees. 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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

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

Range and Azimuth 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 Range resolution Azimuth resolution Theoretical range resolution: 8.31 m ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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 Range PSLR Azimuth PSLR ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

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: +1.45 dB Mean: -15.6 dB ISLR Spurious Sidelobe Levels ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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

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

ENVISAT Cal/Val Workshop – ESRIN – 9/13 December 2002 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