An improved thermo-time domain reflectometry method for determination of ice contents in partially frozen soils

作者：Tian, Zhengchao; Ren, Tusheng; Kojima, Yuki; Lu, Yili; Horton, Robert; Heitman, Joshua L.^*

来源：Journal of Hydrology, 2017, 555: 786-796.

DOI：10.1016/j.jhydrol.2017.10.055

• Thermo-TDR probe
• Soil ice content
• Heat capacity-based approach
• Thermal conductivity-based approach

Measuring ice contents (theta(i)) in partially frozen soils is important for both engineering and environmental applications. Thermo-time domain reflectometry (thermo-TDR) probes can be used to determine theta(i), based on the relationship between theta(i), and soil heat capacity (C). This approach, however, is accurate in partially frozen soils only at temperatures below -5 degrees C, and it performs poorly on clayey soils. In this study, we present and evaluate a soil thermal conductivity (lambda)-based approach to determine theta(i), with thermo-TDR probes. Bulk soil lambda is described with a simplified de Vries model that relates lambda to theta(i). From this model, theta(i); is estimated using inverse modeling of thermo-TDR measured lambda. Soil bulk density (rho(b)) and thermo-TDR measured liquid water content (theta(i)) are also needed for both C-based and lambda-based approaches. A theoretical analysis is performed to quantify the sensitivity of C-based and lambda-based theta(i) estimates to errors in these input parameters. The analysis indicates that the lambda-based approach is less sensitive to errors in the inputs (C, lambda, theta(i), and rho(b)) than is the C-based approach when the same or the same percentage errors occur. Further evaluations of the C-based and theta(i)-based approaches are made using experimentally determined theta(i), at different temperatures on eight soils with various textures, total water contents, and rho(b). The results show that the lambda-based thermo-TDR approach significantly improves the accuracy of theta(i) measurements at temperatures <=-5 degrees C. The root mean square errors of lambda-based theta(i), estimates are only half those of C-based theta(i). At temperatures of -1 and -2 degrees C, the lambda-based thermo-TDR approach also provides reasonable theta(i), while the C-based approach fails. We conclude that the lambda-based thermo-TDR method can reliably determine theta(i), even at temperatures near the freezing point of water (0 degrees C).

• 出版日期2017-12
• 单位中国农业大学