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.

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During previous field experiments in the North Sea it was often assumed that the water column in such shallow coastal tidal waters is vertically well mixed and stratification was neglected when discussing the Normalized Radar Cross Section modulation caused by the sea floor. In this paper the influence of quasi resonant internal waves with the sea bed on the radar imaging mechanism of submarine sand waves itself is investigated. In situ data of the tidal current velocity and several water quality parameters such as sea surface temperature, fluorescence, and beam transmittance were measured in the Southern Bight of the North Sea in April 1991. Simulations of the total NRCS modulation caused by sand waves and internal waves as a function of the current gradient or strain rate induced by the internal wave current field at the sea surface have been carried out using the quasi-steady approximation and linear internal wave theory. As a first approximation the strain rate depending on stratification was calculated using the two-layer model. These simulations demonstrate that at least a density difference between the two layers of the order of ∆ρ ≈ 1 kg m-3 is necessary for a sinusoidal thermocline to effect the total NRCS modulation considerably. The NRCS modulation as a function of wind friction velocity has been calculated independently and is discussed with regard to the strain rate of the surface current field caused by the superimposed imaging mechanisms of sand waves and internal waves. It turned out that the existence of a surface roughness-wind stress feedback mechanism cannot be excluded.

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