Satellite radar scatterometer (NSCAT) studies of ocean surface stress in near coastal regions

Abstract

Summary form only given. This study addresses the consistency of the surface friction velocity derived from the scatterometer normalized radar cross section (NRCS) measurements and the directional properties of the NRCS (SIGMA-O) measurements in near coastal regions. NSCAT data (Level 1.7) colocated with numerous NDBC buoys is being analyzed to determine the variability of the directional properties of the colocated fore and aft beam measurements. These orthogonal measurements of the NRCS (25 km resolution, and converted to linear power units) by the fore and aft beams are used to calculate the Fourier series coefficients of the azimuthal model: AO and A2. The spatial variability of A2/AO, as an indication of how the azimuthal modulation varies, is being examined in the vicinity of buoys off the U.S. Atlantic coast, in the Gulf of Mexico and along the coast of California. Preliminary results show excellent agreement between the satellite derived friction velocity (u*) using the FASINEX/Weissman Ku-band model function and buoy measurements. An alternate method of estimating u* using the satellite (Level 2.0) wind speeds and a drag coefficient produce results with a wider scatter about the buoy-derived estimates of u*. Other results show some cases in which the A2/AO term is relatively constant for the 12-to-19 SIGMA-O cells that lie within the 10 square region centered about each buoy, and other situations in which the A2/AO values vary randomly and considerably even though the winds appear to be uniform. These latter situations are of strong interest, and are being studied to determine the possible causes of this variability. Under consideration are the long wave systems, atmospheric stability and surface material properties.