X-BAND MICROWAVE BACKSCATTERING FROM OCEAN WAVES

Backscattering experiments at microwave frequencies were conducted off the west coast of Scotland in the summer of 1991. Using a dual-polari zation, eight-frequency, X band, coherent scatterometer mounted on the bow of a boat, we measured time-resolved backscattering from ocean wa ves at a range of grazing angles from 10 degrees to 70 degrees. From t he grazing-angle-dependent signals and their Doppler spectra, we are a ble to differentiate Bragg scattering from non-Bragg scattering and re solve ''peak separation'' between the vertical and horizontal polariza tions. We observe instances of ''super'' events, i.e., instances when the horizontal polarization return power equals or exceeds the vertica l polarization power at particular frequencies. We find that ''super'' events occur not only at low grazing angles but at any grazing angle for upwind viewing directions and obtain statistics for Such occurrenc es as a function of grazing angle. We study the coherence properties o f scatterers and find strong evidence that at low grazing angles, life time-dominated, non-Bragg scattering contributes noticeably to returns of both polarizations, but is dominant in providing returns for the h orizontal polarization. We examine ''spiking'' events and find that th ey can be related to, but need not be limited to, breaking wave events . By comparing the data of upwind runs with cross-wind and circle runs , we obtain wind direction dependence of Doppler spectra, which furthe r assists in the identification of scattering mechanisms.