A detector for determining snow water content based on attenuation of cosmic radiation

Water content of the snow pack is measured at approximately 100 sites within the State of California by snow sensors. The sensors detect the water content as a weight exerted on either stainless steel or rubber bladders filled with fluid. The tanks are connected to either a stilling well with a shaft encoder or a pressure transducer. The resulting signal is proportional to the weight of the water in the snow. These sensors suffer from a variety of problems. They require a large footprint, at least 7.5 square meters to avoid edge effects, with consequent environmental disruption. The tanks and associated plumbing are prone to puncture from both human and animal disturbance. Transport of the bladders poses significant t difficulties in wilderness areas where mechanical transport is prohibited. Loss of the sensors for an entire season is not uncommon due to water intrusion into the transducer or leaks in the tanks. Adding insult to injury, the sensors do not accurately measure the water content under certain conditions. Extensive ice layers in the snow can support part of the pack's weight so that the registered water content is less than actual. Later, after these layers lose some of their structure, or additional snow accumulates to collapse the bridging structure, the sensor readings will reflect actual snow water content.This paper will describe the development of a detector which measures cosmic radiation and determines the snow water equivalent based on the attenuation of the radiation. The detector has had two seasons of field verification tests at the Central Sierra Snow Laboratory with very promising results.