SAR Altimetry: New Perspectives for Coastal Studies
Labroue, Sylvie1; Raynal, M.2; Moreau, T.1; Boy, F.3; Picot, N.3; Dibarboure, G.1; Amarouche, L.1

The Cryosat-2 altimeter is operated almost continuously over ocean, either in Low Resolution Mode (like conventional pulse-limited altimetry sensors) or in the so-called Doppler/SAR mode (higher-resolution and lower noise level). This paper shows the results obtained with a new Cryosat-2 demonstration data set derived from the Marine Collaborative Ground Segment project (MCGS). This data set aims at promoting SAR mode over coastal areas and inland waters as a collaborative effort to ESA ground segments (Cryosat-2 and Sentinel-3) and CNES dedicated coastal altimetry products derived from conventional altimetry (PISTACH products).

While pulse limited altimetry provides a resolution between 5 and 10 km due to the size of the radar footprint, the delay Doppler altimetry on board Cryosat-2 provides a true 300 m resolution. This capacity should allow, in most of the coastal configurations, in retrieving good data up to less than 1 km from the coast compared to standard altimetry which is corrupted at 5 to 10 km from the coast. Furthermore, promising results show that this new technique helps to reach smaller spatial scales compared to standard altimetry (30 km wrt 70 km). This paper illustrates these two major improvements through several examples located in areas with different regimes (sea state and oceanic currents) and different coastal configurations.

Another challenge of SAR altimetry is to provide a seamless transition with LRM data, especially in the perspectives of Sentinel-3 which will acquire data in SAR mode only over coastal areas, operating in LRM mode over open ocean. Results are shown on the quality of sea level at the transition between both modes.