Spatial Distribution of the Tuolumne River Basin

Spatial distribution of snow water equivalent across the Tuolumne River Basin from April 10 to June 1, 2013 as measured by NASA's Airborne Snow Observatory.

Flying aboard a Twin Otter aircraft, the Airborne Snow Observatory measures two properties most critical to understanding snowmelt runoff and timing: snow depth and snow reflectivity. By combining snow depth with estimated density, snow water equivalent -- the amount of water in the snow -- is derived and used to calculate the amount of water that will run off. Snow reflectivity, or albedo, is the fraction of the incoming amount of sunlight reflected by snow. Subtracting reflected sunlight from incoming sunlight gives the absorbed sunlight, which largely controls the speed of snowmelt and timing of its runoff.

Map credit: NASA/JPL-Caltech

Note: For more information, see NASA Snow Mapper Reaps Big Benefits for California.