A research team led by the University of Colorado has developed a new way to measure snow depth and water levels using traditional GPS technology, a method that could change the way scientists study the climate.
GPS antennas receive a signal directly from a satellite that enables them to display information about their specific location. In reality, some of the signal from the satellite is actually reflected off the ground, walls and other objects and then received by the antenna after most of the signal has already hit.
Long dismissed by scientists as purely interference, the reflected signal is the basis for the CU team's study, which was released Thursday. By measuring how late the reflected signals hit the GPS antenna, the researchers are able to calculate how much of a certain object -- in this case snow and water -- was present to interfere with the signal.
"You can think of it as measuring the 'echo,'" said CU professor Kristine Larson, who led the study.
Using known values, the team can take the time it took for the reflected signal to hit the antenna and figure out the depth of the snow on the ground or amount of moisture in the soil in the area around the GPS.
Larson said she came up with the idea for the study about five years ago, when she was experimenting using GPS devices as seismographs to calculate the intensity and location of earthquakes.
"My results were completely contaminated by reflections," she said. "I was getting reflections off a water tower that were as big as the actual earthquake. I went from being irritated to thinking how I can actually use these signals."
Larson and other researchers have set up GPS stations at various locations, including a field site in Marshall. Last spring, researchers were able to use GPS signals to calculate the depth of the snow that fell at the Marshall site during two large storms.
Most recently, the group has been working with Munson Farms in Boulder, setting up GPS devices that enable farmers to measure the precise moisture content of the soil and vegetation.
"It allows us to see the moisture content of the entire field, rather than one particular spot," said farm owner Bob Munson, adding that taking moisture readings from only one spot can have a negative effect on the treatment and quality of the harvest.
Larson said she hopes to collaborate with the Boulder-based UNAVCO research group, which has more than 1,000 GPS receivers throughout the Western part of the country. UNAVCO uses the GPS receivers to study plate tectonics, and Larson said she wants to study snow and moisture levels as well.
The technology can be used in the same way to measure the levels of water vapor in the atmosphere, according to John Braun, a member of the University Corporation for Atmospheric Research and co-author of the study.
Larson said the new technique could prove beneficial for meteorologists and scientists who study climate.
"The climate people run these models and make projections based on water levels," she said. "And, they don't really have a good way of measuring these things."
Braun hopes the new technique will help future efforts to deal with water scarcity.
"Water scarcity is going to be a problem for the western United States in the coming century," he said. "Having improved observations of water in all of its phases is going to be an important step as we monitor changes in the environment, which is the most intriguing part of the project for me."