Enhanced visible radiance due to clouds adjacent to a clear-air fields of view in satellite measurements: Cloud adjacency effect

We examined a potential error in atmospheric and surface proper-ties derived from satellite-borne visible sensor for broken cloud fields by using Monte Carlo technique. When clouds lie on the and-solar side of a cloud-free satellite field of view (FOV), some parts of solar radiation reflected from clouds are scattered by the atmosphere in FOV and will enhance observed visible radiances. The enhanced radiance leads to a bias in the inferred properties from calculations with one-dimensional radiative transfer model assuming a cloud-free atmosphere. The bias is a function of the distance of the adjacent cloud from fields of view, the solar zenith angle, etc. Optically thicker and closer clouds to the fields of view lead to a larger enhanced radiance. The bias of 10% appears at a nadir viewing angle for a cloud optical thickness of 9 at a wavelength of 0.49 mum, a solar zenith angle of 30degrees, and surface albedo of 0.1.