Backscatter from the ocean surface under low wind conditions

The University of Massachusetts C-band scatterometer (C-SCAT) participated in the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). Twenty-one missions were flown over the warm pool region of the South Pacific from November, 1992 to February, 1993. During ten of these missions the surface winds were under 4 m s^-1. Preliminary results from data collected at 20°, 30°, 40°, and 50° incidence by C-SCAT show significant spatial variability in the normalized radar cross section (NRCS). Strong azimuthal modulations on the order of 20 dB are observed in these measurements. The minima of these modulations fluctuate substantially in the position end magnitude over areas less than 1 km ². As spatial averaging is performed (size of the footprint is increased), smoothing of the azimuthal modulation occurs. The effects of this spatial averaging on the measurements of the NRCS under low-wind conditions is investigated. The validity of estimating the surface wind vector with a spaceborne scatterometer, whose foot print is typically greater than 50 km×50 km, is discussed