Effective reflectance of oceanic whitecaps.

The effective reflectance of the foam on the ocean surface together with the fraction of the surface covered with foam describes the optical influence of whitecaps in the solar spectral range. This effective reflectance is found to be -22% in the visible spectral range and is presented as a function of wavelength for the solar spectral range. With the fraction of the surface covered with foam, taken from the literature, the results lead to a good agreement with satellite measured radiances and albedo values. The effective reflectance is more than a factor of 2 lower than reflectance values used to date in remote sensing and radiation budget studies. Consequently, the optical influence of whitecaps can be assumed to be much less important than formerly supposed.