Fast and accurate estimation of solar irradiance on Martian slopes

A general parameterization is proposed in this study to calculate, in a Mars-like dusty atmosphere, the solar irradiance reaching an inclined surface, assuming the value in the horizontal case is known. Complete Monte-Carlo radiative transfer calculations, using the Ockert-Bell et al. (1997) dust optical properties, enable the validation of the method for Mars. The total shortwave flux reaching the surface is composed of three contributions: direct incoming flux, reflected flux by surrounding terrains, and scattered flux by the atmospheric dust. The main difficulty is the parameterization of the latter component. We show that the scattered flux reaching the slope can be expressed by a physically-based simple formula involving one empirical coupling matrix and two vectors accounting for the scattering properties and the geometrical settings. The final result is a computationally efficient parameterization, with an accuracy in most cases better than 5 W.m^-2. Such a fast and accurate method to calculate solar irradiance on Martian slopes (should they be topographical surfaces or solar panels) is of particular interest in a wide range of applications, such as remote-sensing measurements, geological and meteorological models, and Mars exploration missions design.