The directional characteristics of the thermal emissivity and reflectivity of a model water surface roughened by wind are analytically studied. The study of emissivity and reflectivity is of importance for accurate measurement of the temperature distribution of a wind-roughened water surface by infrared thermal imaging. Our statistical model of a water surface assumes that the surface displacements are a two-dimensional Gaussian random process whose spectrum is specified by the Joint North Sea Wave Project (JONSWAP) wave spectral model. The effective emissivity and the effective bistatic reflectivity of the water surface in the presence of the shadowing effect are derived. They can be determined by three external parameters: wind velocity, wind direction, and wind fetch. Numerical results show that, as the surface wave grows, the effective emissivity tends to increase at distances far from the detector. This fact indicates that the measurable distance for a wind-roughened water surface may be extended somewhat farther than that for a flat water surface.
© 1994 Optical Society of America
Original Manuscript: September 3, 1993
Manuscript Accepted: November 22, 1993
Published: June 1, 1994
Kyu Yoshimori, Kazuyoshi Itoh, and Yoshiki Ichioka, "Thermal radiative and reflective characteristics of a wind-roughened water surface," J. Opt. Soc. Am. A 11, 1886-1893 (1994)