Ka‐band backscattering from water surface at small incidence: A wind‐wave tank study

We report on an experiment conducted at the large Pytheas wind‐wave facility in Marseille to characterize the Ka‐band radar return from water surfaces when observed at small incidence. Simultaneous measurements of capillary‐gravity to gravity wave height and slopes and Normalized Radar Cross Section (NRCS) were carried out for various wind speeds and scattering angles. From this data set we construct an empirical two‐dimensional wave number spectrum accounting for the surface current to describe water surface motions from decimeter to millimeter scales. Some consistency tests are proposed to validate the surface wave spectrum, which is then incorporated into simple analytical scattering models. The resulting directional NRCS is found in overall good agreement with the experimental values. Comparisons are performed with oceanic models as well as in situ measurements over different types of natural surfaces. The applicability of the present findings to oceanic as well as continental surfaces is discussed.