Monitoring snow grain size for passive microwave studies

The application of passive microwave radiometry to the remote sensing of snow properties is based the ratio of emitted to scattered portions of the upwelling radiation. Increased scattering is indicative of increased snow amount (i.e., the number of snow grains present). However, scattering is directly proportional to snow grain size for a given snow amount. Current snow cover retrevial algorithms produce inaccurate results when snow grain size are unusually large. Therefore, it is necessary to characterize snow grain size on a regional scale (and perhaps a local scale in extreme situations) in order to adjust passive microwave retrieval algorithms. Preliminary analysis indicates that: (1) retrieval algorithms are not as sensitive to grain size as theory would indicate; (2) average grain size data may serve to characterize the detailed stratigraphy of the total snow cover, and; (3) conditions in subfreezing snow which produce cover-climate relationships which can be modelled or monitored on a regional scale.