A New Approach to the Retrieval of the Sea Wave Slopes from Spectrometer SWIM Data

Abstract

Existing of a constellation of remote sensing satellites makes it possible to quickly collect information about the near surface wind field over the World Ocean. A significantly smaller amount of information about sea waves is available to researchers, which stimulates the development of new radars. In 2018, the Chinese-French satellite CFOSAT (Chinese-French Oceanic SATellite) was launched into orbit with a SWIM spectrometer on board. SWIM (Surface Waves Investigation and Monitoring instrument) is designed to measure the two-dimensional spectrum of long waves with oblique sounding (small incidence angles) and the significant wave height at a zero incidence angle. At present the measurements at small incidence angles in the direction perpendicular to the direction of flight are performed by precipitation radars from TRMM (Tropical Rainfall Measuring Misson) and GPM (Global Precipitation Measurement) satellites. Due to the rotation of the SWIM antenna system around the vertical axis, for the first time, an orbital radar performs measurements at different azimuthal angles at small incidence angles. The performed theoretical analysis showed that this measurement scheme allows one to retrieve the mean square slopes (mss) of large-scale, in comparison with the radar wavelength, waves. The input parameters of the new algorithm are the backscattered radar cross section at zero incidence angle and the azimuthal dependence of the radar cross section at one incidence angle. As a result of processing, it is possible to retrieve a two-dimensional slope field for the case of single-mode waves or mixed waves (wind waves+swell) in the presence of a dominant wave system. It is planned to process the data and analyze the information received to assess the accuracy of the retrieval algorithm.