83rd Annual

Tuesday, 11 February 2003
Inference of snow pack properties of grain size, density and stratification from microwave signatures of snow cover
Cezar Kongoli, NOAA/NESDIS, Camp Springs, MD; and N. C. Grody
Compared to visible and infrared radiation, in the microwave region, many snow pack physical properties (e.g., depth, snow water equivalent, density, grain size, wetness and stratification) can significantly affect the microwave response. Therefore, development of inversion techniques to recover properties of interest, and in particular, snow water equivalent and depth, is a daunting challenge for the current microwave research. The many snow pack properties that affect the microwave signal can be either sources of error if ignored, or sources of additional information if exploited. Since longer wavelengths penetrate the snow pack to greater depths, comparison of different bands and spectral signatures of snow cover can help in recovering important snow cover information about stratigraphy, density, grain size and the age of the snow pack. It has been recently recognized that snow structural changes, and especially grain size, significantly impacts the reliability and accuracy of global snow depth retrieval algorithms. Currently, the performance of these algorithms is poor because effects of important snow pack physical properties have been ignored. Examples using the Advanced Microwave Sounding Unit (AMSU) measurements at 23, 31, 89 and 150 GHz will be provided to demonstrate the effects of the various snow parameters on the microwave observations.

Time series of AMSU measurements in the 23-150 GHz range are compared with time series of weather variables and snow cover properties, obtained through synoptic weather stations and snow hydrologic modeling at several representative locations in the US. Analysis includes the study of response patterns of several linear combinations of brightness temperatures (TB) at low and high frequency channels: TB23-TB31, TB23-TB89, and TB89-TB150. Results show that higher frequency channel combinations of TB23-TB89 and TB89-TB150 respond strongly to new, lower density, finer grained snow pack, and that response patterns of these combinations can help in inferring grain size information. In contrast, lower frequency channels generally respond to new snow weakly, irrespective of the amount of snow on the ground. Analysis of patterns also reveals important information about snow stratification.

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