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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
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
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 characteristics3
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

aps product examples
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

aps product examples5
APS Product Examples

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

ceos offset test
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

irf analysis
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

irf function
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
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

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

strange azimuth responses
Strange azimuth responses

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

range and azimuth pslr
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

islr and spurious sidelobe levels
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

azimuth ambiguities
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
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

cross talk
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

noise equivalent rcs
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

scalloping
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 / 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

conclusions
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