From the Boulder Daily Camera (Laura Snider):
[Ethan Gutmann, a scientist at the National Center for Atmospheric Research] and his colleagues are testing a number of new snow-measuring devices both at NCAR’s Marshall Field Site south of town and at the Niwot Ridge weather station northwest of Nederland.
Today, there are manual methods of measuring snow — think ruler — and automatic methods of measuring snow. Ultrasonic snow depth sensors, for example, essentially send out a pulse of noise and measure how long it takes for the sound waves to bounce back from the snow surface. But sounds waves can be altered by temperature and wind speeds. “In addition to the ultrasonic snow depth sensors, people are starting to use lasers,” Gutmann said. “It’s the same basic principles, but you’re using light instead of sound. And lasers aren’t affected by things like wind and temperature of the air.”
Gutmann is now using a laser measuring device at Niwot Ridge that can take a measurement of a different spot every four seconds. But he’s hoping to win the support of the National Science Foundation to install a laser that can take 12,000 measurements a second, which would allow him to quickly get a picture of how snow is piling up across a landscape. “I don’t want to know the snow depth 12,000 times per second,” he said. “But we want to study snow processes — we want to study the when and why. If you can scan a point and it takes you five days to get back to it, it’s hard to learn much about the processes.”
Gutmann is also working with a collaborator at the University of Colorado, Kristine Larson, to work on ways to use GPS sensors to measure snow depth. When GPS sensors receive satellite signals, they record both the signal that directly hits the device and the signal that bounces off the ground before hitting the sensor. “The receiver you have can’t distinguish between the two,” Gutmann said. “But the reflected signal causes a little bit of noise in the dominant signal that it’s looking at.” That noise changes as the distance between the GPS receiver and the ground changes, like after a snowfall. Using GPS signals to measure snowfall is especially interesting, from a cost efficiency perspective, because existing GPS receivers that are in place around the world could be used for the task.
At the Marshall Field Site south of Boulder, NCAR scientists are also developing instruments for measuring the amount of precipitation that falls during a snowstorm. These sensors, which contain some antifreeze, melt the snow as it falls, and measure the weight of the newly melted precipitation. In terms of gaining a full picture of total precipitation from a storm, these sensors have the benefit of measuring all the water in the snow, whereas snow depth measuring devices may inaccurately gauge precipitation when snow melts before it accumulates. The sensors, though, can be affected by wind.