Determining Surface Solar Absorption from Broadband Satellite Measurements for Clear Skies: Comparison with Surface Measurements

Abstract

Two separate datasets both of which provide measurements of net downward shortwave radiation have been combined, so as to provide a means of critically examining methods for transferring satellite measurements to the surface. This is further facilitated through interfacing the two datasets with an atmospheric shortwave-radiation model. One dataset comprises near-surface measurements made at the Boulder Atmospheric Observatory Tower while the other consists of collocated satellite pixel measurements from the Earth Radiation Budget Experiment. This study amplifies previous suggestions that surface-shortwave absorption is a more meaningful quantity, for climate studies, than is surface insolation. The former should not, however, be evaluated from the latter through use of a surface albedo, since surface albedo is not solely a surface property nor can it easily be evaluated from satellite measurements. It is further demonstrated that a direct evaluation of surface shortwave absorption can be more accurately obtained from satellite measurements than can surface insolation. Specifically, a linear slope-offset relationship exists between surface and surface-atmosphere shortwave absorption, and an algorithm is suggested for transferring satellite shortwave measurements to surface-shortwave absorption. The present study is directed solely at clear-sky conditions because the clear-sky top-to-surface transfer serves as a necessary prerequisite towards treating both clear and overcast conditions.