Microwave radar cross sections and doppler velocities measured in the surf zone

Normalized radar cross section (NRCS) and Doppler velocity are estimated from microwave measurements at near-grazing angles, and in situ fluid velocities are measured with acoustic Doppler velocimeters (ADVs). Joint histograms of radar cross section and Doppler velocity cluster into identifiable distributions.

The NRCS values from pixels with large NRCS and high Doppler velocities (>2 m/s) decrease with decreasing bore height to the shoreline, similar to scattering from a cylinder with decreasing radius. The Doppler velocities associated with these regions in the histograms agree well with theoretical wave phase velocities. Radar and ADV measurements of fluid velocities between bore crests have similarly shaped energy density spectra for frequencies above about 0.1 Hz, but energy levels from the radar are an order of magnitude higher than those of the ADV data.