On-board encoding of the ENVISAT wave mode data

The synthetic aperture radar sensor on the ENVISAT remote sensing satellite will utilize a data reduction system called Flexible Block Adaptive Quantization (FBAQ). This technology will allow the 8 bits/sample SAR signal data to be reduced to 4, 3, or 2 bits/sample, as specified by the mission controller. For wave mode operation, in which small SAR "vignettes" are acquired over oceanic regions, the 8 to 2 bits/sample mode of FBAQ must be employed due to on-board storage limitations. The authors quantitatively evaluate the effect of the FBAQ data reduction on the power spectra of the vignettes, obtained using ESA wave mode processing methods. Using ERS-1 SAR signal data modified to reflect the properties of ENVISAT SAR data, the authors show that the use of the 2-bit FBAQ algorithm will yield power spectra results better than those currently available from ERS-1, with the degree of improvement dependent on the distribution shape of the SAR signal data and the radiometric variation within the vignette.