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WWRC 85-17(h)
Snowpack Estimates From Satellite Imagery and Relationships to Spring Melt Patterns


Snowpack has traditionally been monitored by selected, on-site recording stations and periodic sampling for water content. These procedures are proven effective, but may be improved by augmenting these procedures with new techniques that employ satellite imagery for obtaining regional estimates of the snowpack. Landsat imagery obtained during the late winter, spring, and summer each year record the depletion of snowpack during the spring and summer melt. The area of snowpack can be efficiently estimated using an automatic electronic planimeter coupled with a video density analysis system. The laboratory measurements of snowcover for each area of snowpack can be plotted together with data from selected stream gauges to derive an empirical relationship between snowcover and discharge. With several years' data, the empirical relationships can be refined to the extent that it can be used as a tool for forecasting runoff.

Over the past two years we have made a concerted effort to establish an image data base from which to define the critical snow-melt patterns in each Wyoming drainage area where snowmelt contributes significantly to the water supply. Snowcover measurements have been made and the data evaluated relative to appropriate streamflow data. In most cases, three or four years' satellite data have been used to establish a predictor relationship that allows estimates to be made of expected annual runoff, volume of peak runoff, and duration of the snowmelt season. Most of these predictor equations can now be employed in runoff estimation that can supplement the runoff projections derived by more conventional means. As each years satellite data are evaluated and discharge volumes are measured, the new data can be incorporated into the forecasting system to improve the definition of the predictor equations and the accuracy of future water-supply forecasts.

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