Doppler modelling of radar sea clutter

Data from a cliff top radar experiment conducted off the south coast of England are examined in order to investigate the applicability of a three-component 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 polarisation and Doppler characteristics, and decorrelation times. This analysis confirms the presence of the same Bragg and non-Bragg scattering mechanisms as observed in the laboratory wave tank. A dependence of each of the scattering mechanisms on wind direction can also be inferred, showing that Bragg resonant scattering from capillary waves and non-Bragg scattering from highly disturbed white water after a wave has broken are present in both the up and 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-component 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 underlying gravity waves can be extracted from the Bragg scattering polarisation ratio via the composite surface scattering model.