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NW Fishletter #368, April 3, 2017
 NASA Tests Snow-Sensing Technologies To Improve Water Supply Forecasts
Accurately measuring how much snow is on the ground and how water is stored in that snow is still a challenge for scientists.
NASA is working on changing that. On Feb. 16, the agency announced it had completed its first flights in a multi-year research effort to ascertain which technologies work best to measure snow in different conditions.
The research campaign, called SnowEx, is being conducted in Grand Mesa, Colo. The location was chosen for its varying forest-cover densities.
Having accurate and available measurements is key to forecasting in the Northwest, where most of the annual streamflow for drinking water, hydropower, fish and irrigation comes from mountain snow pack.
"While the results are a long way off, they could be helpful in our region," said Kevin Berghoff, a hydrologist with the Northwest River Forecast Center.
Detecting snow through trees and occasional vandalism to equipment can be problems in the Northwest, where remote and usually high-elevation SNOTEL sites rely on sensors to measure precipitation and temperatures, which are then transmitted via radio signal to recording stations.
This year's conditions highlight another problem, Berghoff told NW Fishletter. "We don't have a good handle on the amount of snow we have at lower elevations."
In parts of the Snake River basin, there have been record amounts of snow at high elevations. But there are no good estimates of how much has accumulated at lower levels, making it difficult to predict run-off volumes and potential flooding, Berghoff said.
The NASA research could make a difference if it gives us more clues on lower-elevation snow, he said.
Smiley Mtn. SNOTEL, Idaho, 9,520 ft. Credit: Natural Resources Conservation Service
According to a NASA news statement, satellites have so far been unreliable in determining the snow-water equivalent (SWE), which is the amount of water the snowpack holds.
Currently, SWE can be measured in the field or calculated using a combination of remote sensing observations and modeling, as is done in the Northwest.
NASA research flights will carry a range of remote-sensing instruments, including microwave sensors that measure SWE in dry snow; thermal infrared cameras and remote thermometers for calculating surface temperature; and laser devices that measure snow depth.
Another important device on board will be an imaging spectrometer that measures snow albedo--the amount of sunlight reflected and absorbed by snow, which determines the speed of snowmelt and runoff timing.
With changes in the climate and different rates and timing of snowmelt, the information collected by an imaging spectrometer could have a far-reaching impact. Changes in snowmelt patterns can affect spring flooding, stream temperatures and water supplies.
NASA and its team of cooperating scientists from across the United States and elsewhere will evaluate how each sensor performs in measuring snowpack and its properties and how the sensors could best work together.
The knowledge gleaned from these multiple-sensor flights will be used to shape a space-based mission to measure snow across the earth, according to the NASA news statement. It will also help in figuring out how measurements from existing satellites that are designed for other purposes could be used to evaluate global snow-water equivalents.
This past fall the NASA research program flew a lidar device to determine baseline pre-snow conditions. Incorporated in the research is a thorough ground-truthing program of field measurements and sampling that will validate sensor data.
Meanwhile, in the Northwest, the best information available indicates this year's snowpack in the Columbia basin and west of the Cascades is significantly above average. Hydrologists and meteorologists hope they are working with good numbers that can help regional managers handle runoff, water supply and reservoir storage. -Laura Berg
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