Sun glitter radiance and radar cross‐section modulations of the sea bed

Abstract

Aircraft and satellite‐borne multispectral sensors such as ocean color scanners, spectrometers, and scanning Lidar's have proved to be effective in detecting submarine shallow‐water bottom topography in clear coastal waters. For such studies the blue‐green band of the visible electromagnetic spectrum (wavelength between 400 and 580 nm) is used, because natural light in this range has the deepest penetration into the water column. However, if the water becomes turbid, the reflection from the submarine sea bed disappears. In this case the only possible mechanism available in the optical range of the electromagnetic spectrum for detecting surface signatures of shallow water bottom topography is through the observation of direct sunlight specularly reflected from a roughened sea surface, known as sun glitter radiance. As the tidal flow over irregularities on the submarine sea bed creates surface roughness variations, sun glitter imagery can be used to detect such features. In this paper a first‐order theory of the sun glitter imaging mechanism of submerged sand waves is presented. The results of sun glitter radiance modulations are compared with simulations of P band radar cross‐section modulations and with experimental data. Calculations of both the constant background sun glitter radiance and the sun glitter radiance modulation show that these parameters are very sensitive to wind speed, to view angle with respect to acquisition time, and to observation geometry as a whole.