Determination of snowpack properties from satellite passive microwave measurements

The use of satellite microwave data to determine snowpack properties is investigated through calculation of theoretical microwave brightness temperatures and comparison of the computed brightness temperatures with actual satellite microwave measurements. Archived data from the Nimbus-5 and Nimbus-6 Electrically Scanning Microwave Radiometers (ESMR), as well as data from the Nimbus-7 Scanning Multifrequency Microwave Radiometer (SMMR), are analyzed for a study area in the north-central United States. The results of the investigation indicate that snow boundaries can usually be defined by the 37-GHz or 18 (19) GHz data because of the sharp decrease in brightness temperature when going from land to a snow surface. For dry snow conditions, the 37 GHz data display a decrease in brightness temperature with snow depth due to the stronger volume scattering effect of the deeper snow; at 18–19 GHz, the sensitivity to snow depth is not as significant. The onset of snowmelt can be determined at both microwave frequencies investigated (18–19 GHz and 37 GHz) because of the significant increase in the brightness temperature with melting due to the decrease in volume scattering that occurs in the presence of free water.