Normalized radar backscattering cross-section and Doppler shifts of the sea surface in Ka-band

Field data taken from the Black Sea Research platform during 2009-2015 are used to develop a dual-co-polarized (VV and HH) empirical model for the sea surface normalized radar cross-section (NRCS) and Doppler Velocity (DV) in the Ka-band. A fitting function for the NRCS is the standard truncated Fourier series in azimuth with polynomial coefficients dependent on incidence angle and wind speed. The data are corrected for the angular antenna pattern, which is measured in special calibration procedures. The resulting NRCS model is consistent with other rare Ka-band measurements and agrees well with Ku-band geophysical model functions, in contrast with previously proposed Ka-band models. Surface is subtracted from measured DV using either propeller current meter measurements or surface video recording. The resulting DV model consists of constant and wave-induced (WIDV) parts. The constant part is evaluated based on the time mean of Instantaneous DV (IDV), which is close to the Bragg wave phase speed. The WIDV part is analyzed in terms of Modulation Transfer Function (MTF) for which a separate empirical model is proposed.