Estimates of snow water equivalent derived from measurements of the attenuation of terrestrial gamma radiation are systematically biased downward if variability in the snow water equivalent exists in the snowpack. The degree of underestimation is a function of both the shape and the variance of the distribution. The effects of these two factors on the estimate of snow water equivalent are examined for three assumed distributions (discrete, normal, and uniform) over a wide range of variances. The downward bias that results in each of the examined distributions can be corrected if the variance in the snow water equivalent is known. Examples of the application of the methodology are provided for flight lines located in the plains of western Canada and in the mountainous region of Colorado. The methodology presented can aid National Weather Service hydrologists in improving river and flood forecasts, water supply forecasts, and spring flood outlooks for large areas of the United States and Canada.
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Carroll et al. (1989) studied this question.