Analysis and Optical Processing of Sea Photographs for Energy Spectra

An optical Fourier transform analysis of a sea photograph taken under a particular skylight irradiance has been proposed by Stilwell [1] as a means of providing a quantitative description of the sea-vector wave-number spectrum. The process requires an explicit knowledge of the skylight irradiance reflected from the sea surface to the aerial camera. A first-order analysis shows that the photographic density of the transform recording is functionally related to the sea-slope spectrum, provided that the average optical density measured in the sea photographic negative is approximately linear. The analysis of the process and some experimental results are discussed.