Evaluation of Snow Water Equivalent by Airborne Measurement of Passive Terrestrial Gamma Radiation

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Abstract
Recent research studies have investigated an airborne gamma radiation detection system to determine the water equivalent of snowpacks in nonmountainous areas. Snow attenuates natural gamma emissions from the soil, and the magnitude of attenuation is related to the mass of the water blanket between the soil and the detector. Gamma spectral and total counting rates are collected and recorded by an airborne system using 14 4‐ by 4‐inch sodium iodide (NaI (Tl)) crystals. These data are corrected for soil moisture, background radiation, and effects of air density. Extensive snow depth and density measurements were taken to determine ‘ground truth’ water equivalent under the flight path. Results of the first year of research indicate that gamma spectral data may be expected to give areal measurement of snow water equivalent within at least 0.2–0.5 inch over favorable terrain. The use of total count data is even more promising but requires methodology still under development for eliminating background interference.

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