SNOW HYDROLOGY PROCESSES AND REMOTE-SENSING .2.

In the last 20 years remote sensing research has led to significant pr ogress in monitoring and measuring certain snow hydrology processes. S now distribution in a drainage basin can be adequately assessed by vis ible sensors. Although there are still some interpretation problems, t he NOAA-AVHRR sensor can provide frequent views of the areal snow cove r in a basin, and snow cover maps are produced operationally by the Na tional Weather Service on about 3000 drainage basins in North America. Measurement of snow accumulation or snow water equivalent with microw ave remote sensing has great potential because of the capabilities for depth penetration, all-weather observation and night-time viewing. Se veral critical areas of research remain, namely, the acquisition of sn ow grain size information for input to microwave models and improvemen t in passive microwave resolution from space. Methods that combine bot h airborne gamma ray and visible satellite remote sensing of the snowp ack with field measurements also hold promise for determining areal sn ow water equivalent. Some remote sensing techniques can also be used t o detect different stages of snow metamorphism. Various aspects of sno wpack ripening can be detected using microwave and thermal infra-red c apabilities. The capabilities for measurement of snow albedo and surfa ce temperature have direct application in both snow metamorphism and s nowpack energy balance studies. The potentially most profitable resear ch area here is the study of the bidirectional reflectance distributio n function to improve snow albedo measurements. Most of the remote sen sing capabilities in snow hydrology have been developed for improving snowmelt-run-off forecasting. Most applications have used the input of snow cover extent to deterministic models, both of the degree day and energy balance types. Snowmelt-run-off forecasts using satellite deri ved snow cover depletion curves and the models have been successfully made. As the extraction of additional snow cover characteristics becom es possible, remote sensing will have an even greater impact on snow h ydrology. Important remote sensing capabilities will become available in the next 20 years through space platform observing systems that wil l improve our capability to observe the snowpack on an operational bas is.