Experimentally motivated model for low grazing angle radar Doppler spectra of the sea surface

A model is presented for the Doppler spectra of low grazing angle radar backscatter from the sea surface, and is compared with data collected in the large wind–wave tank at the Ocean Engineering Laboratory (OEL) of the University of California, Santa Barbara (UCSB). The components of the Doppler model are based on the findings of an experiment conducted at the OEL in which synchronous radar and high speed video data were recorded, coupled with surface slope information gathered at the tank using a laser slope meter. The synchronous radar and video data allow the clear identification of the surface conditions giving rise to Bragg scattering, and two distinct types of non-Bragg scattering. Each of the scattering mechanisms is found to have markedly different polarisation and Doppler characteristics. The Doppler model is found to provide a good description of the radar data over a wide variety of radar frequencies and wave types, including mechanically generated breaking waves.