Full spectrum broken cloud scene simulation

Abstract

This paper discusses the effects of broken cloud fields on solar illumination reaching the ground. Application of aerosol retrieval techniques in the vicinity of broken clouds leads to significant over prediction of aerosol optical depth because of the enhancement of visible illumination from the scattering of photons from clouds into clear patches. These illumination enhancement effects are simulated for a variety of broken cloud fields using the MCScene code, a high fidelity model for full optical spectrum (UV through LWIR) spectral 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 (RT), 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. The paper includes an overview of the MCScene code and a series of calculations for broken 3D cloud fields demonstrating the effects of clouds on downwelling flux.