A spectral model for correcting sunglint and skyglint

Abstract

Specular reflections of the sun and the sky at the water surface (sunglint, skyglint) can be of comparable intensity or even much higher as the water leaving radiance, even for observation geometries minimizing the sunglint. A number of approaches have been developed for correcting these glint signals, practically all based on the near infrared spectral signature, but none of them is working reliably under all conditions. Challenges are the determination of the actual glint intensity and its wavelength dependency. The wavelength dependency of the reflected radiance (Lr) differs in general significantly from that of the downwelling irradiance (Ed), hence the ratio Lr/Ed is not a constant, but has a characteristic spectral signature that is mainly determined by scattering in the atmosphere. An analytic model has been developed describing intensity and wavelength dependency of sunglint and skyglint with few parameters. It has been implemented into the publicly available software WASI for forward simulation and inverse modeling of radiance and reflectance measurements. The ambiguity of parameter determination during inversion is discussed, and results from applying the model to field measurements are presented.