MONITORING THE DRY DENSITY AND THE LIQUID WATER-CONTENT OF SNOW USINGTIME-DOMAIN REFLECTOMETRY (TDR)

Knowledge of the liquid water content of snow is important in snowmelt simulation, avalanche control and runoff modeling. Presently, there i s a need for fast, accurate and non-destructive methods to measure sno w wetness to validate data obtained by remote sensing techniques. In t his study, the primary objective was to develop relations between snow liquid water content, snow density anti dielectric constant. The liqu id water content, the snow density and the dielectric constant were ob tained by the freezing calorimetry technique, with a U.S. Army Cold Re gions Research and Engineering Laboratory (CRREL) corer and with the t ime domain reflectometry (TDR) technique, respectively. The empirical relationship between the liquid water content and the dielectric const ant yields an error of estimate of 1.0% by volume and a mean absolute error of 0.8. When little liquid water exists, the dry snow density ca n be evaluated by the: TDR method with a mean absolute error 0.03 g/cm (3). For short instrument-to-probe cable length, matching the impedanc e between the cable and the probe with a transformer did not improve t he precision nor the accuracy of the measurements. The second objectiv e was to develop and test different experimental probe designs that co uld he used to continuously monitor the in situ liquid water content o f a snowpack at different levels. Three types of horizontal probes wer e tested and transmission line probe made of 0.3 cm diameter parallel rods provided the best results.