Doppler modelling of radar sea clutter

Data from a cliff top radar experiment conducted off the south coast of Eng land are examined in order to investigate the applicability of a three-comp onent model for radar Doppler spectra, developed using laboratory wavetank data, to coastal water sea clutter. This is achieved by a detailed analysis of the prominent features in the cliff top radar data in terms of polarisa tion and Doppler characteristics, and decorrelation times. This analysis co nfirms the presence of the same Bragg and non-Bragg scattering mechanisms a s observed in the laboratory wave tank. A dependence of each of the scatter ing mechanisms on wind direction can also be inferred showing that Bragg re sonant scattering from capillary waves and non-Bragg scattering from highly disturbed white water after a wave has broken are present in both the up a nd down wind cases, while the highly polarised HH 'sea spikes' appear only when the radar is looking into the wind. It is shown that the three-compone nt Bragg-whitecap-spike model for Doppler spectra is able to describe both the up and down wind cases well, and that the RMS tilt angle of the underly ing gravity waves call be extracted from the Bragg scattering polarisation ratio via the composite surface scattering model.