SCATTERING FROM BREAKING GRAVITY-WAVES WITHOUT WIND

Scattering experiments from breaking gravity waves conducted at a wave tank facility at small grazing angles in the absence of wind are anal yzed, Breaking gravity waves are studied using a fully plane polarimet ric horizontal (HH), vertical (VV), vertically transmitted and horizon tally received polarization (VH), and horizontally transmitted and ver tically received polarization (HV) pulse-chirped X-band radar in conju nction with optical instruments: the plane polarimetric optical specul ar event detector (OSED) and side-looking camera(SLC), Spatially and t emporally resolved radar backscatter has been measured and temporally correlated to the data obtained from the optical diagnostics. The expe riments yield the following results: 1) enhanced scattering compared t o Bragg scattering levels occurs throughout the evolutionary process o f wave-breaking, i.e., the radar scatters strongly from both the unbro ken and broken surfaces; 2) an explanation is found for the observatio n that the scatterer Doppler frequency is slightly less than the Doppl er frequency corresponding to the fundamental wave phase speed; 3) a r epresentative non-Bragg cross section of a breaking wave can be obtain ed; and 4) a breaking wave surface is found to be an efficient depolar izer.