Advances in thermo‐time domain reflectometry technique: Measuring ice content in partially frozen soils
Zhengchao Tian, Yuki Kojima, Joshua L. Heitman, Robert Horton, Tusheng Ren
Abstract
Abstract Ice content (θ i ) is a critical parameter affecting soil thermal, mechanical, and hydraulic properties in cold regions. Few techniques are available for accurately determining θ 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 θ i . The thermo‐TDR method determines θ i by using a heat‐capacity‐based ( C ‐based) approach or a thermal‐conductivity‐based (λ‐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 θ i values at temperatures below −5°C, but it fails at higher temperatures. The λ‐based approach, which solves for θ i from thermo‐TDR measurements with an iterative method, gives more accurate θ 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 λ‐based thermo‐TDR method is preferred for determining θ i in partially frozen soils.