Microwave Emission From Snow and Glacier Ice

Abstract

The microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

Estimation of snow depth in the UK using the HUT snow emission model

“…In general, the strength of upwelling scattering signal is proportional to SD/SWE and it is this relationship that forms the basis for estimating the snow pack characteristics (Chang et al 1976, Ulaby and Stiles 1980, Foster et al 1997, Tsang et al 2000, Pulliainen and Hallikainen 2001.…”

Siberia snow depth climatology derived from SSM/I data using a combined dynamic and static algorithm

“…Over the last 20 years, several algorithms have been developed to estimate snow depth or snow water equivalent. These algorithms are based on radiative transfer calculations using Mie scattering theory (Chang et al, 1976) or using a dense media model based on the quasi crystalline approximation and sticky particle theory (Ding et al, 1994;Tsang, 1992, Tsang et al, 2001. These studies indicate that the brightness temperature has a strong dependence on the snow grain size.…”

Remote sensing of snow extent

“…Snow is efficient at scattering microwave radiation emitted from the Earth's surface, since snow grain dimensions are often similar to microwave wavelengths, resulting in a diminished signal measured at the satellite from snow-covered surfaces (Chang et al, 1976;Schanda et al, 1983;Matzler, 1994). Microwave scattering by ice crystals is frequency-dependent, enabling the use of two or more bands to estimate SWE (Chang et al, 1987;Grody and Basist, 1996), although other methods have been evaluated such as one based on the inversion of a snow emission model (e.g., Pulliainen and Hallikainen, 2001).…”