SWIM: A Multi-Incidence Beams Ku-band Real Aperture Radar for the Observation of the Ocean Wave Field Spectra

The instrument SWIM (Surface Waves Investigation and Monitoring) on the CFOSAT (Chinese French Oceanographic Satellite) project aims at measuring the directional spectra of ocean waves on a 180 km wide swath. Orbiting on a 500 km sun-synchronous orbit, it provides with a global full coverage of the oceans between -80 and 80deg. It consists in a real aperture radar (RAR) operating in Ku-band (13.575 GHz) on 6 distinct beams pointing at incidence angles from 0deg (nadir) to 10deg, while scanning the whole azimuth angles (0-360deg). The nadir beam is similar to the one provided by a standard altimeter. Its main objective is to measure the significant wave height and wind speed (from the measurement of the radar cross section). Radar cross-sections are also estimated from 2 to 10deg off-nadir observations, then ensuring the access to profiles dependence with incidence and azimuth angles. Appropriate processes of observations at 4 to 10deg incidence provide with an estimate of the spectral properties of the local wave field.