snow blown into the container and how much is fallen snow. Another problem occurs when both snow and rain fall before the observer has time to change the gauge. In all of these cases the observer must judge how much of the water is snow and how much is rain. Other snow gauges Automated Remote reading gauges, such as used by weather stations, work similarly to rain gauges. They have a large catch area (such as a drum sawn in half, top to bottom) which collects snow until a given weight is collected. When this critical weight is reached, it tips and empties the snow catch. This dumping trips a switch, sending a signal. The collection then repeats. If the catch container has a heater in it, it measures the snow weight accurately. It is also possible to tip based on volume instead of weight, with appropriate fill sensing. Snow pillow Another snow sensor called a snow pillow looks like a round bag lying on the ground. Inside the pillow is a liquid such as an environmentally safe antifreeze. Usually the snow pillow will be connected to a manometer. The manometer reading will vary based on how much snow is sitting on the pillow. This type of sensor works well for many locations but is more difficult to use in areas of hard blowing snow. References External links Chinese inventions Meteorological instrumentation and equipment Snow Hydrology instrumentation