Whitecaps: spectral reflectance in the open ocean and their contribution to water-leaving radiance

摘要

Abstract: The reflectance of white caps in the open ocean is obtained with a 6-channel spectral radiometer, extended from the bow of a ship, at wavelengths; 410, 440, 510, 670 and 860 nm. In addition to reflectance data, air/water temperature, wind speed and direction are obtained as well as GPS information in order to characterize ocean surface conditions. A visual reference for sea surface conditions measured by the radiometer is recorded using a video camera mounted beside the radiometer. By measuring a small area of the water surface over time, the presence and spectral influence of whitecaps can be quantified.Using this technique the spectral reflectance of individual whitecaps can be measured and tracked through their complete life cycle. Also, integration over a larger time series of ocean surface reflectance data provides a measurement of the augmented or extra contribution from white water reflectance to the water leaving radiance observed by ocean color satellites. Estimates of the augmented reflectance are subsequently correlated to sea surface state, and include the frequency of occurrence and spectral contribution from various levels of white water reflectance as whitecaps grow and decay. !18