Correcting Satellite Passive Microwave Brightness Temperatures in Forested Landscapes Using Satellite Visible Reflectance Estimates of Forest Transmissivity

Forest cover attenuation of microwave emission is a significant challenge to the estimation of snow accumulation from remote sensing microwave observations because canopy biomass attenuates the understory snowcover emission and produces additional emission to that generated by the snowpack and subnivean surface. Transmissivity of radiation is an important variable that describes how a tree canopy attenuates microwave emission from the ground. Although it can be measured in the field or estimated by models using field data at the in situ scale, the estimation of transmissivity at regional to global scales is a challenge. Following the work of Metsämäki et al. (2005), a transmissivity model that uses reflectance data from the moderate resolution imaging spectroradiometer is applied to estimate transmissivity at global scales. The influence of the vegetation attenuation and the emission on the brightness temperature (Tb), which is observed by advanced microwave scanning radiometer-Earth observing system sensor (Tb
_vegetation
), can be calculated by comparing the Tb of the ground below-canopy (Tb
_ground
) with the Tb above the forest canopy (Tb
_ac
) during the presnow season. Linear regression models derived between transmissivity estimates and the Tb
_vegetation
had significant R
²
values of 0.76 (0.96) at 18 GHz vertical (horizontal) polarization and 0.91 (0.91) at 36 GHz vertical (horizontal) polarization.