Measurements of the backscatter from the ocean by the microwave scatterometer

The radar backscatter from the ocean were measured by using a 16.0 GHz pulsed wave scatterometer. Experiments were performed either off-shore tower instrumentations or low flying aircrafts. Normalized radar cross section, NRCS, obtained from the received signals was compared with the surface wind speed which directly measured by the anemometer. On the tower experiments, all results were derived from a time series of radar backscatters of the sea surface illuminated by a pencil-beam, and various features of the NRCS were found for windward azimuth angles within about . On the airborne experiments, the NRCS characteristics were found over the azimuth angle by circle flight measurements, and indicate the anisotropic backscatters in the open sea covered with wind waves. The measured azimuth distribution of the NRCS in log space can be well expressed as a cosine series function up to the fourth term and the upwind direction can be determined by the profiles of the first and second terms. The present results are discussed comparing with the model function for the Seasat-A seatterometer.