The effect of whitecaps and foam on wind speed extraction with a pulse limited radar altimeter

Abstract

The effect of whitecaps and foam on wind speed extraction with a pulse limited radar altimeter has been studied using a specular point model. By modelling foam and water as a two-layer media, we have investigated the changes in reflectivity as a function of thickness using electro-magnetic field theory. Our analysis indicated a change of reflectivity from a value of 0.617 at 13.9 GHz normal incidence to a value of 0.10 for a foam thickness of less than 1 cm. The values of reflectivity computed from a two-layer model compared fairly well with these derived using an emissivity model. The modified specular point model gave an improved relationship between σ^o and wind speed in comparison to Brown's model. The Seasat altimeter's data analysis over the Arabian sea and the Bay of Bengal gave an rms difference of 2.2 m/sec in wind speed retrieval using the present modified model and Brown's model.