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A snow pillow measures the water content of snowpack, snow that accumulates on the ground. Such measurements are important for health and safety in areas where there are concerns about avalanches and other events. They can also help meteorologists make predictions about water resources, as melting snowpack is a significant source of water in some regions. There may also be concerns about the quality and depth of snow in areas where winter sports like skiing are popular, or in communities where roof cave-ins caused by snow are a known issue.
The device consists of sheets of stainless steel forming an airtight pillow filled with an antifreeze solution. The snow pillow is carefully calibrated so that as snow settles on the steel and displaces the antifreeze, the equipment can measure the hydrostatic pressure. This is the pressure created by water at rest, and provides information about how much water is present in the snowpack. Since snow can fall in a variety of ways and may be of varying density, just knowing the depth of the snow isn’t enough to determine how much water it contains.
One advantage of the snow pillow design is that it can be automated. The measurements generated by the equipment can be transmitted by radio or satellite to a base station. Weather observation stations may include thermometers, wind sensors, and other devices that all return data. This allows for the collection of key information in remote areas that would be difficult or impossible to access in the winter months. Multiple stations may be deployed at key points, sometimes with multiple snow pillow installations to ensure that equipment failure doesn’t make it impossible to collect measurements.
Manufacturers of scientific instruments sometimes produce snow pillows along with accessory equipment. It is also possible to fabricate them, an approach taken in some regions. At the time the device is installed, scientists may also insert probes into the ground to collect temperature and soil moisture data. A snow pillow does require periodic maintenance, which can be performed in the summer months when it is safe to enter remote areas.
Equipment at weather stations can be damaged by harsh weather as well as animal activity. Some are also prone to vandalism, for a variety of reasons. If a station is located in an area where vandalism is a problem, it may be fenced and posted with no trespassing signs to deter unwanted human visitors. If researchers cannot collect data from one or more stations, this could impede their ability to make accurate weather and water supply predictions.