Sea spikes at moderate incidence and their relation to position on the waves

Most models of radar backscatter from the sea ignore sea spikes, the nonlinear effects that result in large excursions above the local mean signal. They are strong enough to change the mean scattering level significantly, and they may cause streaks in synthetic aperture radar (SAR) ocean images. A threshold based on short signal excursions above the local mean is used to identify spikes. With this method, spikes can be found in regions of low signal level. An autoregressive spectral method is used to identify the locations of the spikes on the dominant waves. Sample results from Ka-band measurements in the North Sea made during the SAXON-FPN experiment are given. It is shown that spikes can occur anywhere on the dominant wave, although they are most prevalent on the front face.