Infodoc : Sciences, Techniques et Culture

An approximate explicit formula has been developed for the Earth-atmosphere system nadir-beam reflectivity a8,View the MathML source, where r is the object pixel reflectivity, a is the effective reflectivity of the surrounding terrain, is the cosine of the solar zenith angle, B, F, and W, respectively, are the backward-scattering, forward-scattering, and absorption optical thickness, and g(μ0) is the anisotropy of atmospheric backscattering to zenith from the direct beam. This formula is accurate only for limiting cases of low optical thickness and should not be used for quantitative atmospheric correction unless Still, the expression affords a good insight into atmospheric effects on radiometric imaging and may be useful under circumstances when B, W, and F are not measured during a [...]

An approximate explicit formula has been developed for the Earth-atmosphere system nadir-beam reflectivity a8,View the MathML source, where r is the object pixel reflectivity, a is the effective reflectivity of the surrounding terrain, is the cosine of the solar zenith angle, B, F, and W, respectively, are the backward-scattering, forward-scattering, and absorption optical thickness, and g(μ0) is the anisotropy of atmospheric backscattering to zenith from the direct beam. This formula is accurate only for limiting cases of low optical thickness and should not be used for quantitative atmospheric correction unless Still, the expression affords a good insight into atmospheric effects on radiometric imaging and may be useful under circumstances when B, W, and F are not measured during a satellite pass. The significance of the terms 2aBr and (a—r)F, which describe the adjacency effect, i.e., the effects of reflection from the terrain surrounding the object pixel and subsequent scattering, is discussed, (a8—r) is calculated from this formula and analyzed in terms of how this difference affects the possibility and the accuracy of measuring the surface albedo and of thematic mapping by matching the measured multispectral radiometric data against compiled spectral signatures. Subsequently, the derivative da8/dr is analyzed, showing how the atmosphere decreases this derivative for low reflectivities, thereby reducing discrimination capability for thematic mapping in any mode. Finally, contrast transmittance through the atmosphere, which affects the possibilities of photointerpretation is discussed. The adjacency effects lead to ambiguity in the concept of contrast transmittance, which is resolved through the use of several definitions.