Sea surface spectrum from aerial photographs: Laboratory model studies

Abstract

We have experimentally studied the optical spectrum of daylight photographs of sinusoidal and other complex reflecting surfaces made out of paper coated with a thin layer of plastic. It is shown that the reflecting characteristics of the plastic layer are quite similar to those of the water surface. Hence, the paper models can be conveniently used to model the sea surface undulations. The main results of the present laboratory study are: The frequency of a sinusoidal surface is best estimated when the camera angle is about 45° and the illumination angle is also 45°. Clear skylight illumination produces more accurate estimates than those obtained with diffused illumination. The amplitude of the sinusoidal surface must be less than one third ($\text{1}\text{3}$) of its wavelength so that no higher harmonics are generated and the spectral peak height is proportional to the waveheight.

Finally, this study verifies through laboratory model studies some of the theoretical conclusions previously reported using order theory. The photographic method for studying the spectrum of the sea surface is perhaps the cheapest of all other methods used by oceanographers.