Lasers, GPS Measure Snowfall

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Knowing the amount of snow isn't just important to skiers. Scientists and water resource managers need that info too. But measuring snow isn't as easy as just sticking a ruler into the ground into a snowbank. And snow gauges don't always pick up accurate readings in windy weather.

To fix this issue, scientists have turned to devices that use GPS signals and laser pulses to get a more accurate reading of how much snow has fallen in a given region.

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At the National Center for Atmospheric Research, geologist Ethan Gutmann, a postdoctoral fellow, is developing a laser instrument that can measure snow depth over an area the size of a football field. The laser sends light pulses that can read depths to within a half an inch, forming a grid pattern made of 1,000 different points. The result is a 3-D picture of the snow, which shows contours, making it much easier to calculate how much is there. Doing the same thing with snow gauges would be next to impossible.

The big limitation on lasers is that they can't see through anything solid, so if you put them in wooded areas, you need more than one covering the same stretch of ground.

Lasers are great, but if you want to see snow cover over really wide swathes of the country, there's no better vantage point than orbit. That's where GPS comes in. Gutmann and colleague Kristine Larson at the University of Colorado are looking at how GPS sensors can pick up signals that bounce off the ground to measure snow cover. Snow shifts the frequency of the signals in a way that bare soil does not, and that shift tells scientists how deep the snow is.

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While there's the advantage of an existing GPS network, it's still not completely clear how snow density and surface roughness affect the signals, so there is still some work to be done. 

All this may seem like a lot of effort to measure snowfall, but it is important for more than weather forecasting and climatology. Snow depth is a critical factor in assessing avalanche risk, or whether to close airports; thus anything that makes it simpler and cheaper to measure the snow will be welcome -– in addition to meaning that fewer people will have to trudge out with yardsticks.

Via University Corporation for Atmospheric Research

Top Photo: Ethan Gutmann checks out his laser instrument that can measure snow depth.

Credit: UCAR/Carlye Calvin

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