Doppler characteristics and angular dependence of radar backscatter from laboratory breaking waves

Radar backscatter measurements were conducted on transient breaking waves in a 330 foot laboratory wave facility. The radar measurements were taken using a dual polarization K-band (24.125 GHz) CW Doppler radar positioned at various azimuth angles relative to the direction of wave propagation. Backscatter measurements were made for low energy (minimal whitecapping) and high energy (considerable whitecapping) spilling breaking waves. The peak radar cross section (RCS) was found to be the same for both breaking waves and occurred in the upwave look direction, just prior to whitecapping. Azimuthal radar measurements yielded variations on the order of 17 dB with the lowest RCS values occurring in the crosswave direction. The Doppler spectra of the upwave radar returns contained a narrow peak corresponding to the phase speed of the underlying long waves. The downwave radar returns yielded broad Doppler spectra corresponding to distribution of velocities