An impact analysis of the surface-cloud damping effect on TOA reflectivity using A 3D radiative transfer model

Abstract

The I3RC Community Monte Carlo model of three-dimensional (3D) radiative transfer (I3RC-CM) was improved by specifying surfaces with a widely used bidirectional reflectance model known as the RPV (Rahman-Pinty-Verstraete). The surface-cloud damping effect on top-of-atmosphere (TOA) reflectivity (hereafter, the damping effect) is evaluated as the atmospheric attenuation of incoming shortwave radiation on its way down to the surface and shortwave radiation reflected at the surface that is transmitted back to the TOA. A series of simulations were performed using the improved I3RC-CM to investigate this effect over different land covers, in which the land covers are characterized by the 3 RPV parameters: the intensity of surface reflectance, the anisotropy of the surface, and the asymmetry parameter. The damping effect is greatly affected by the land cover, especially the intensity of surface reflectance. The intensity of surface reflectance can lead to an approximate deviation of 0.40 in the damping effect, while the influence of the asymmetry parameter and the surface anisotropy on the damping effect is less than 0.10. The damping effect strengthens as the surface reflectance intensity and asymmetry parameter increase, but slightly weakens as the surface anisotropy increases. The land cover change has a stronger impact on the damping effect at the absorbing wavelengths than at the non-absorbing wavelengths due to the cloud absorption, particularly at 2.13 µm, but the cloud absorption offers only a partial explanation for the differences in damping effect changes with values less 0.10.