Advances in thermo-time domain reflectometry technique: Measuring ice content in partially frozen soils

Ice content (theta(i)) is a critical parameter affecting soil thermal, mechanical, and hydraulic properties in cold regions. Few techniques are available for accurately determining theta(i) in laboratory samples and in situ. A combined heat-pulse and time domain reflectometry (thermo-TDR) sensor, which measures soil thermal properties and electrical properties simultaneously, can be used to estimate theta(i). The thermo-TDR method determines theta(i) by using a heat-capacity-based (C-based) approach or a thermal-conductivity-based (lambda-based) approach. Here, we describe the principles and procedures of such approaches. The C-based thermo-TDR approach is simple to use and provides reasonable theta(i) values at temperatures below -5 degrees C, but it fails at higher temperatures. The lambda-based approach, which solves for theta(i) from thermo-TDR measurements with an iterative method, gives more accurate theta(i) estimates than does the C-based approach and extends the thermo-TDR measurement range to temperatures near the freezing point of water. Therefore, the lambda-based thermo-TDR method is preferred for determining theta(i) in partially frozen soils.