A major theme of progress in snow hydrology over the past quadrennium has been the expanded use of remote sensing for determining snow properties, which then are used to estimate snow distributions and snowmelt runoff. There has also been a move toward development of physically based snowmelt models to use with this emerging data, particularly for alpine areas. The coupling of remote sensing and physically based approaches will enable making not only more-accurate basin-scale forecasts, but will also provide spatially distributed estimates of snowmelt.
Both visible and near-infrared, and passive microwave remote sensing data are being used to develop estimates of snow-covered area for operational forecasting of snowmelt, much of which is currently done using conceptual models. Development of accurate snow-cover information for areas with steep, variable topography requires higher resolution data than are currently available from operational remote sensing instruments. Models using the higher-resolution satellite data expected during the next decade show good results with test data acquired from aircraft platforms. Determination of other snowpack properties in alpine areas, such as grain size and albedo (from visible/infrared) and snow-water equivalence (from active microwave) are topics of continuing research. Progress in both algorithm development and testing with field data sets shows that obtaining these properties is achievable. The volume integrating capability of microwave remote sensing has received much attention, because it offers the possibility of remote determination of whole snowpack properties. However, the lack of multipolarizing SAR will limit the ability to reliably estimate SWE in alpine areas.
Progress in snow chemistry is also producing a more detailed understanding of snowpack and snowmelt processes, which is needed for integrated modeling to address ecological and global-change questions.
This authors' research is supported in part by National Science Foundation and in part through the National Aeronautics and Space Administration's Earth Observing System program. The second author was also a 1993 recipient of the American Geophysical Union's Horton fellowship. R. Brice did the manuscript preparation.