Snow Wetness Influence on Impulse Radar Snow Surveys Theoretical and Laboratory Study

The snow-water equivalent of late-winter snowpack is of utmost importance for hydropower production in areas where a large proportion of the reservoir water emanates from snowmelt. Impulse radar can be used to estimate the snow-water equivalent of the snowpack and thus the expected snowmelt discharge. Impulse radar is now in operational use in some Scandinavian basins. With radar technology the radar wave propagation time in the snowpack is converted into snow-water equivalent with help of a parameter usually termed the a -value. Use of radar technology during late winter brings about risk for measurements on wet snow. The a -value for dry snow cannot be used directly for wet snow. We have found that a liquid-water content of 5% (by volume) reduces the a -value by approximately 20%. In this paper an equation, based on snow density and snow liquid water content, for calculation of wet-snow a -value is presented.