Sentinel-3 SRAL Altimeter Data Quality Analysis and a Comparison between LRM and SAR Mode
Picot, Nicolas1; Boy, Francois1; Desjonqueres, Jean-Damien1; Borde, Franck2; Mavrocordatos, Constantin2; LE ROY, Yves3; HOUPERT, Alexandre3

The Sentinel-3 Mission (S-3) is part of the Global Monitoring for Environment and Security (GMES/Kopernikus) European initiative. For oceanic applications, the S-3 mission will deliver continuity to existing ones ESAs ERS, Envisat and CryoSat missions with ocean/land colour data, sea/land surface temperature estimates and sea surface and land ice topography at least at the level of corresponding Envisat instruments, the Medium Resolution Imaging Spectrometer (MERIS) and the Advanced Along-Track Scanning Radiometer (AATSR) and the Envisat Radar Altimeter (RA).

The nadir looking SAR altimeter concept has been studied in parallel in ESA and the US since the mid-1990s. This concept is now implemented in SIRAL instrument operating on board Cryosat-2 mission launched early 2010, and dedicated to ice topography observations. However, this novel altimeter concept can be very advantageous for observation of ocean surfaces, as it promises improved altimetric precision and better along-track resolution than conventional pulse-limited altimeters. In theory, there is several advantages with this mode as it should allows to obtain high-resolution and high-accuracy altimetric mapping of the ocean. Several studies are on-going to develop and test suitable processing algorithms for this new altimeter mode.

We will present in this paper the data quality assessment performed on CNES and CLS side. First the advantages and drawbacks of the SAR and LRM modes will be illustrated, focusing on ocean surfaces but also including the coastal and inland water bodies. Then we will present the analysis of Sentinel-3 SAR data acquired on ground during the development of this instrument and the results obtained thanks to the ESA SPS simulator. Finally, we will present the results obtained on CryoSat data as the altimeter designs are very close between both missions.