by Sean Morris
Scientists at the National Center for Atmospheric Research (NCAR) are working to improve the accuracy of snow measurements on the ground using specialized lasers and GPS technology.
For years snowfall has been measured with snow gauges and yardsticks. However, snow amounts can greatly vary within a single field or neighborhood. Ultimately, snow measurements using the traditional methods do not provide an accurate picture of the amount of snow on the ground.
Getting accurate snowfall measurements is very important for a number of reasons. Emergency managers rely on snowfall measurements to determine where snow plows are needed. Accurate snowfall measurements can also be used to determine whether or not airports will be shut down or highways closed. Measurements are also used to determine whether or not avalanches are a threat or if melting snow will result in significant flooding.
The methods that are now used to measure snowfall can greatly under- or over-estimate the amount of snow that falls in a region. According to NCAR, during windy conditions, such as blizzards, snow gauges miss up to a third of the snow that has fallen in a particular area. Some snow gauges are protected by fencing to reduce the wind’s impacts, but even with the fences, the amounts can be very inaccurate.
Observations of snowfall amounts are also determined by using a flat, white piece of board known as a snow board. The procedure used to check for snowfall using a snow board is inefficient, requiring weather observers to check the boards every three hours and clear them every six hours. The National Weather Service’s cooperative Observer Program and the community Collaborative Rain, Hail and Snow Network (CoCoRaHS) involves thousands of volunteers nation-wide using snow boards to record snow depth. Their reports are only filed once a day.
To improve snowfall measurements, researchers are now testing a laser instrument to measure snowfall across very large areas. Recent tests by NCAR scientist Ethan Gutmann show that a laser instrument, installed above a tree line in the Rocky Mountains west of Boulder, can measure ten inches or more of snow with an accuracy of up to one-half inch.
“If we are successful, all of a sudden these types of instruments will reveal a continually updated picture of snow across an entire basin,” Gutmann says.
There are a few limitations to using laser beams to measure snow fall. The beams can’t penetrate objects such as trees or buildings. To work around this, Guttman and Kristine Larson, a colleague at the University of Colorado, is working on measuring snowfall using GPS sensors. GPS signals bounce off of snow at a different frequency than they do when they bounce off of bare ground. By measuring the change in frequency they are able to determine how much snow is on the ground. But like the laser beam method, there are a few drawbacks to using GPS signals. The roughness of the snow and the density of the snow can alter the signals.
“Our hope is to develop a set of high-tech tools that will enable officials to continually monitor snow depth, even during an intense storm,” Larson says. “While we still have our work cut out for us, the technology is very promising.”
“I think this technology has great potential to benefit emergency managers and other decision makers, as well as forecasters,” Gutmann says.