Estimating the Variance of Airborne Snow Water Equivalent Estimates Using Computer Simulation Techniques

Estimates of snow water equivalent derived from measurements of the attenuation of terrestrial gamma radiation vary as a function of several known sources of error. In this study, a computer simulation of the physically-based model used to obtain estimates of snow water equivalent is developed and the variance in estimates of snow water equivalent is investigated using simulation techniques. Several of the principle sources of error in the estimating model are simulated and studied for various conditions under which snow water equivalent estimates are obtained. The simulation results indicate that the error in airborne snow water equivalent estimates made in both forested and open environments with up to 60 cm of snow water equivalent is less than 12 per cent of the estimate for typical flight lines. The results of this study 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.