NASA mission targets more accurate snowpack data

NASA Airborne Snow Observatory measurements of snow water equivalent (top image) and snow albedo, or reflectivity (bottom image) for the Tuolumne River Basin in California’s Sierra Nevada on April 21, 2013. The snow water equivalent measured the total water contained as snow in the basin on that date at 375 million cubic meters, or enough to fill the Rose Bowl about 1,180 times. The albedo map expresses the percentage of sunlight reflected back to space by the snow. The lower the albedo, the faster the snowmelt rate and runoff. Image credit: NASA/JPL-Caltech.

Aerial surveys with high-tech instruments will create detailed snow maps, yielding better runoff forecasts

FRISCO — Data from an ambitious new NASA aerial program could help resource managers get a jump on global warming, with more precise and timely snowpack measurements.

By Summit Voice

NASA’s Airborne Snow Observatory began it’s three-year demonstration mission in April, with weekly flights over the Tuolumne River Basin in California’s Sierra Nevada and monthly flights over Colorado’s Uncompahgre River Basin. Scientists involved in the program hope to start covering the entire Upper Colorado River Basin.

The data is already paying off for power companies and water managers, who can use real-time updates to allocate water resources more efficiently, for storage, irrigation and municipal supplies.

Most snowpack measurements are currently collected via ground-based surveys and from automated SNOTEL sites. Airborne mapping can cover more ground and gather data from areas without observation stations, resulting in more accurate forecasts.

Instead of having a few scattered readings and filling in the gaps, the new lidar and specrtometer data creates detailed regional snowpack maps. The instruments can calculate snow depth to within about 4 inches (10 centimeters) and snow water equivalent to within five percent. Data are processed on the ground and made available to participating water managers within 24 hours.

“The Airborne Snow Observatory is on the cutting edge of snow remote-sensing science,” said Jared Entin, a program manager in the Earth Science Division at NASA Headquarters in Washington.

Tom Painter of NASA’s Jet Propulsion Laboratories at the California Institute of technology, said the mission fills a critical need in an increasingly thirsty world, initially focusing on the western United States, where snowmelt provides more than 75 percent of the total freshwater supply.

“Changes in and pressure on snowmelt-dependent water systems are motivating water managers, governments and others to improve understanding of snow and its melt,” said Painter, the mission’s principal investigator. “The western United States and other regions face significant water resource challenges because of population growth and faster melt and runoff of snowpacks caused by climate change. NASA’s Airborne Snow Observatory combines the best available technologies to provide precise, timely information for assessing snowpack volume and melt,” he said.

A scanning lidar system from the Canadian firm Optech Inc. of Vaughan, Ontario, measures snow depth with lasers to determine the first property, snow water equivalent. Snow water equivalent represents the amount of water in the snow on a mountain. It is used to calculate the amount of water that will run off.

An imaging spectrometer built by another Canadian concern, ITRES of Calgary, Alberta, measures the second property, snow albedo. Snow albedo represents the amount of sunlight reflected and absorbed by snow. Snow albedo controls the speed of snowmelt and timing of its runoff.

The mission is a collaboration between NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the California Department of Water Resources in Sacramento.

The flights will run through the end of the snowmelt season, which typically occurs in July. The Tuolumne watershed and its Hetch Hetchy Reservoir are the primary water supply for San Francisco. The Uncompahgre watershed is part of the Upper Colorado River Basin that supplies water to much of the western United States.

Before now, Sierra Nevada snow water equivalent estimates have been extrapolated from monthly manual ground snow surveys conducted from January through April. These survey sites are sparsely located, primarily in lower to middle elevations that melt free of snow each spring, while snow remains at higher elevations.

Water managers use these survey data to forecast annual water supplies. The information affects decisions by local water districts, agricultural interests and others. The sparse sampling can lead to large errors. In contrast, the NASA observatory can map all the snow throughout the entire snowmelt season.

“The Airborne Snow Observatory is providing California water managers the first near-real-time, comprehensive determination of basin-wide snow water equivalent,” said Frank Gehrke, mission co-investigator and chief of the California Cooperative Snow Surveys Program for the California Department of Water Resources.

“Integrated into models, these data will enhance the state’s reservoir operations, permitting more efficient flood control, water supply management and hydroelectric power generation.” Gehrke said the state will continue to conduct manual surveys while it incorporates the Airborne Snow Observatory data.

“The snow surveys are relatively inexpensive, help validate observatory data and provide snow density measurements that are key to reducing errors in estimating snow water equivalent,” he said.

Painter plans to expand the airborne mapping program to the entire Upper Colorado River Basin and Sierra Nevada.

“We believe this is the future of water management in the western United States,” he said.

For more on NASA’s Airborne Science program, visit: .

The California Institute of Technology in Pasadena manages JPL for NASA.


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