From the Boulder Daily Camera (Peter Budoff):
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.