Level-0 Packet Encoding
Raw SAR data compression is used to reduce the instrument data rate to fit the available data downlink. Application of a Block Adaptive Quantisation-like (BAQ) raw data compressor adds quantisation noise to the raw data which degrades the data Signal-to-Noise Ratio (SNR). A BAQ that applies a constant bit rate independent of radar signal power is not optimal. It produces a degradation of the SNR which varies with the power of the detected radar signal. To overcome this, SENTINEL-1 Level-0 data products are compressed using Flexible Dynamic Block Adaptive Quantisation (FDBAQ).
FDBAQ controls the bit rate in a flexible way as a function of the input radar signal power to provide a variable bit rate coding that increases the number of bits to be allocated to bright scatterers. The number of quantisation bits is selected according to a local estimate of clutter-to-noise ratio. This approach leads to a time variant bit rate.
FDBAQ is an improvement over the Entropy Constrained Block Adaptive Quantisation (ECBAQ) used for ENVISAT.
For the data to be usable, it will need to be decompressed following the decompression algorithm detailed in the SAR Space Packet Protocol Data Unit (S1-IF-ASD-PL-0007).