Microwave studies of snowpack properties

Research involving the microwave characteristics of snow was undertaken in order to expand the information content currently available from remote sensing, namely the mesasurement of snow-covered area. Microwave radiation emitted from beneath the snow surface can be sensed and thus permits information on internal snowpack properties to be inferred. The intensity of radiation received is a function of the average temperature and emissivity of the snow layers and is commonly referred to as the brightness temperature (Tb). The Tb varies with snow grain and crystal sizes, liquid water content and snowpack temperature. Multifrequency passive microwave aircraft measurements as well as in-situ measurements were obtained in 1976 and 1977 at Steamboat Springs and Walden, Colorado. The Tb of the 0.8 cm wavelength channel was found to decrease more so with increasing snow depth than the 1.4 cm channel. More scattering of the shorter wavelength radiation occurs thus resulting in a lower Tb for shorter wavelengths in a dry snowpack. Longer wavelengths such as the 21.0 cm can be used to assess the condition of the underlying ground.