"The Wind River Range is a very high mountain range, with lots of snow," said Dorothy Hall, lead author of the study and a senior research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Earlier snowmelt impacts the water resources of most of the state of Wyoming, which has been undergoing a drought since 1999."
Hall and her team analyzed snow maps derived from the NASA-U.S. Geological Survey (USGS) Landsat satellite program, which has been operating since 1972. The scientists sorted through more than 1,000 Landsat scenes to create 227 snow maps for the 42-year period extending from 1972 to 2013. Much of the work to create snow maps for this study could not be automated, Hall said. For example, each map had to be checked manually to make sure clouds were not obscuring the snow in the basin.
Because so few clear-sky Landsat images are available during the snowmelt season, the team developed a method to fill in the gaps. They plotted all available snow extent data for a given decade and used a computer program to fit a curve, connecting the observed data points. This showed the trend of the timing of snowmelt in each decade, though the changes can only be given as an approximation, because there weren’t enough data available to give precise dates.
This video shows the progression of snowmelt in 2013, based on data from the Landsat 7 and the Landsat 8 satellite.