Reflectance retrieval in the presence of optically opaque broken clouds

Abstract

This paper will discuss the effects of broken cloud fields on solar illumination reaching the ground. Broken cloud fields pose a problem for many atmospheric compensation algorithms which retrieve reflectance and/or aerosol properties from measured spectral imagery. In the reflective domain (visible to the SWIR), the application of atmospheric compensation algorithms in the vicinity of broken clouds leads to inaccuracies because of the enhanced number of photons scattered from the clouds into the clear sunlit areas. These illumination effects are simulated for simple slab clouds and complex broken cloud fields using the MCScene code, a high fidelity model for full optical spectrum (UV through LWIR) hyperspectral image simulation. MCScene provides an accurate, robust, and efficient means to generate spectral scenes for algorithm validation. MCScene utilizes a Direct Simulation Monte Carlo approach for modeling 3D atmospheric radiative transfer including full treatment of molecular absorption and Rayleigh scattering, aerosol absorption and scattering, and multiple scattering and adjacency effects, as well as scattering from spatially inhomogeneous surfaces. The model includes treatment of land and ocean surfaces, 3D terrain, 3D surface objects, and effects of finite clouds with surface shadowing.