AN ALGORITHM FOR THE PRECISE LOCATION OF THE SOLAR SPECULAR REFLECTION POINT IN THE VISIBLE BAND IMAGES FROM GEOSTATIONARY METEOROLOGICAL SATELLITES

Space-based remote sensing of the region of specular reflection of sun light from the ocean surface, termed sunglint, is useful for estimatin g the roughness characteristics of the reflecting ocean surface. Techn iques have been developed to estimate near-surface wind speeds over th e oceans based on a study of sunglint signatures in satellite images. The geostationary VHRR visible band imaging provides a veritable store house of sunglint signatures. In this paper, an algorithm for the prec ise location of the principal point of the specular solar reflection i n INSAT-VHRR visible band images is presented and discussed. The princ ipal point of specular reflection of the glitter pattern is estimated by the considering Sun-satellite-Earth geometry and the laws of reflec tion. This is achieved by knowing the position of the Sun and position of the satellite in the appropriate spherical coordinate system. The nonlinear equations thus derived are solved using the Newton-Raphson m ethod. Using the algorithm, the location and movement of the principal point of specular reflection as a function of time of the day and day of the year is studied. An example of observed sunglint signatures in the INSAT-IB VHRR image of 7 August 1987 is analyzed and wind-speed e stimation is presented. The algorithm presented in this paper is gener al and is applicable for the precise location and study of sunglint si gnatures in any other geostationary VHRR imaging sensors. The method p resented also provides the basis for extension of this study to all ot her types of orbiting satellites.