Monitoring the unfrozen water content of soil and snow using time domain reflectometry

Abstract

Time domain reflectometry is a technique that can be used to indirectly measure the in situ moisture content of soil. Previously, this method was not used in the field to continuously monitor the liquid water content because of the influence it had on the wetting, drying, freezing and thawing cycles of the soil. The principal objectives of this field investigation were, apply the TDR technique to monitor the unfrozen water content in the soil, utilize this technique to determine snowmelt infiltration into seasonally frozen soils, and explore the feasibility of using the TDR technique to monitor snowmelt percolation in the snowpack. An additional goal of this paper was to explain in a straightforward manner how to use the TDR technique to obtain the liquid water profile in a soil. Various configurations of parallel transmission lines were installed horizontally at various depths in the soil and also in the snowpack. This technique gave a good delineation of the unfrozen water content with depth in frozen soils. Results looked promising in snow if in situ snow density measurements were taken along with the TDR measurements.