Level 2 Radial Velocity Processing
The SENTINEL-1 Level-2 RVL component consists of an estimate of the total Doppler frequency (Hz) and the corresponding radial velocity (m/s) estimated from a SENTINEL-1 Level-1 Single-Look Complex (SLC) SAR image. The RVL component contains an estimate of the width of the ocean Doppler spectra. The Doppler width is a new geophysical parameter that has never been estimated from SAR data before. For each of these parameters the RVL component contains the corresponding standard deviation of the estimates. The image from which a single RVL is computed can be a SLC imagette from the WV mode, or sub-image extracted from a SM SLC image, IW SLC image or an EW SLC image. The RVL product is given on a grid similar to the OSW or OWI components.
The Doppler frequency is estimated from the SLC data by fitting (least square minimisation) the antenna model to the observed azimuth spectra taking into account effects from additive noise and side-band effects. The Doppler frequency is the total estimated Doppler frequency offset without any geometric or mis-pointing corrections. The corresponding radial velocity is retrieved from the Doppler frequency after correcting the estimated total Doppler frequency for antenna mis-pointing as function of elevation angle and compensating for the attitude/orbit Doppler signal error. As for the OSW and OWI components, the RVL component also contains information on the block size used for estimation. The spatial coverage of the RVL product is equal to the spatial coverage of the corresponding Level-1 WV SLC or sub-images extracted from the Level-1 SM/IW/EW SLC products, limited to ocean areas.
The figure below shows the flowchart of the RVL processing