Microwave response of snow

Abstract Radar observations of snow-covered terrain were made at several test sites over the winter seasons of 1977–1980. Using truck-mounted scatterometers, the backscattering coefficient was measured over the continuous frequency range extending between 1 and 18 GHz and at 35 GHz. In conjunction with the radar measurements, radiometric observations were also made at 10.7 GHz, 37 GHz and 94 GHz during the 1977 winter season. Several types of experiments were conducted to evaluate the dependence of the radar backscattering coefficient (σ o ) and radiometric emissivity (e) on snow depth, wetness, surface roughness, and other snow parameters. The results indicate that volume scattering causes σ o to increase and e to decrease with increasing snow depth until the snow layer appears electromagnetically semi-infinite in extent. The presence of liquid water content in the snowpack results in increased attenuation and reduction in scattering, which leads to less backscatter and more emission by the snow volume. From an application standpoint, the spectral behavior of σ o and e suggest that through proper choice of sensor parameters, microwave sensors have the potential capability for remotely monitoring both the water equivalent and wetness of snowpacks, particularly if both day and night observations are made.

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