Liquid water in a snowpack has been recognized for some time as a quantifiable variable of hydrologic significance. It is also important in the interpretation of snowpack microwave remote sensing data. One effective method for measuring the liquid water content of snow is freezing calorimetry. This technique is presented from theory through application including formulations for calculating the percent of liquid water in the snowpack. Silicone oil has been used successfully as the freezing agent. Consistent results can be obtained with the method, even when using newly-trained operators. Liquid water content data can be obtained approximately every 15 minutes when using two calorimeters and three operators. The freezing calorimetric approach was found to be accurate in determining the liquid water content of the snow to within ± 1.0-2.0 percent by weight.

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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