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