Stray Satellite Signals Help Measure Snowfall in Arid West

DENVER -- Climate scientists are gleaning valuable information about snowfall and droughts from errant satellite signals once considered a nuisance. The data comes from GPS receivers, mostly ones used by earthquake researchers to detect motion in the Earth's surface. The receivers use signals from GPS satellites to measure movement. But there's a problem: In addition to picking up signals directly from the satellites, the receivers also pick up satellite signals that bounce off the ground first, providing false readings. "First I tried to get rid of them because they were making the earthquake data bad," said Kristine Larson, a professor of aerospace engineering at the University of Colorado. But about four years ago, Larson and other Colorado scientists discovered those nuisance signals have some value.

In winter, researchers can determine the depth of nearby snow by how long it takes the reflected signals to reach the receiver. If the ground is bare, they can tell how much moisture is in the soil by the strength of the reflected signal. That can be valuable information, particularly in the arid West, where snow depth in remote mountain ranges determines how much water will be available to cities, farms and wildlife when the spring melt begins.

Larson and a team of researchers now monitor about 500 GPS receivers, mostly in the western United States, for snow and moisture data. The National Drought Mitigation Center at the University of Nebraska-Lincoln uses the information from Larson's team to supplement data from a nationwide snow-measuring network of about 3,000 human observers and more than 730 automated stations called SNOTEL, for Snowpack Telemetry.

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— The Associated Press