Visibility of rms slope variations on the sea surface

A model relating viewing geometry, sky conditions, and statistical sea surface parameters to the luminance of the sea surface is developed. The model is used to estimate the relative visibility of surface perturbations manifested by a variation in the rms surface slope. These estimates are presented for a variety of geometries in the solar plane using two sky conditions (clear and overcast) and two wind speeds (~2 and 7 m/sec). The results of this analysis, applicable to a unidirectional radiometer with no temporal averaging, show comparable extrema in the visibility of surface perturbations for both the overcast and clear sky models. The visibility of surface perturbations is shown to be maximized by geometries with either large gradients in the slope-to-luminance transfer functions (within the glitter pattern for the clear sky and near the horizon for both sky models) or very small gradients in the slope-to-luminance transfer functions (90 degrees away from the glitter pattern for the clear sky and nadir directed for the overcast sky). It is shown that improvements in the estimated values of the luminance SNR sensitivity to rms surface slope variations can be obtained through spatial and/or temporal averaging.