Impact of Swell on SAR-Mode Measurements
Moreau, Thomas1; Amarouche, Laiba1; Thibaut, Pierre1; Boy, Francois2; Picot, Nicolas2

The ability of a SAR-mode altimeter to deliver important new ocean observing capabilities has been amply demonstrated through the exploitation of in-orbit Cryosat-2 data. As expected, this concept provides several advantages over conventional pulse-limited altimeters, such as improved range precision and finer along track spatial resolution. On board the Cryosat-2 mission, the synthetic aperture processing creates doppler bins as narrow as 300 meters in width. This allows to achieve high-resolution high-accuracy altimetric mapping of the ocean surfaces, and might potentially enable to detect some feature that are unresolved from low-resolution mode observations, in particular the ocean surface waves (swell). Very few studies have investigated the sensitivity of the SAR-mode altimeter data to the swell, which is of high importance for the next missions (Sentinel-3 and Jason-CS). For example, it is currently unknown how the retrieved sea surface height elevations and other surface parameters derived from the SAR-mode are impacted and at what accuracy these data are in the presence of directional ocean waves, especially those close to the SAR along track sampling. CLS has been conducting a study, under CNES funding, to characterize these effects through both simulation and flight data analysis. First, this paper presents the numerical study based on the use of an end-to-end simulation tool including a SAR simulation capability with a generator of realistic models of long ocean surface waves and a SAR retracking algorithm. Second, the paper will show some Cryosat-2 SAR-mode data apparently related to swell features.