The correlation of radar sea clutter on vertical and horizontal polarization with wave height and slope

A program of measurements of both the ocean surface contour and the radar echo therefrom was carried out jointly by the Naval Research Laboratory and the Woods Hole Oceanographic Institution in October 1955. The well-known pattern of interference between direct and indirect illumination of a target above the surface of the sea explains all of the results on radar sea clutter observed at long ranges. At shorter ranges and under certain sea conditions there is observed a dependence upon the polarization of the incident radiation. This result requires some additional assumption about the mechanism of sea clutter in a zone between the interference region and the region of specular reflection (large angles of incidence) where the dependence disappears. The radar echo observed using vertically polarized radiation was found to decrease with wind direction in the following order: upwind, downwind, crosswind. For horizontal polarization, downwind and crosswind were found to be interchanged at times depending upon radar wavelength, angle of incidence to the sea, and sea state. The observed mean square slope of the ocean waves in these three directions was found to follow the order observed for vertically polarized radar echoes. A correlation between radar echo and the cross-correlation of water height and slope is shown.