A new thermo-time domain reflectometry approach to quantify soil ice content at temperatures near the freezing point

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Kojima, Yuki
Nakano, Yuta
Kato, Chihiro
Noborio, Kosuke
Kamiya, Kohji
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Horton, Robert
Distinguished Professor
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The Department of Agronomy seeks to teach the study of the farm-field, its crops, and its science and management. It originally consisted of three sub-departments to do this: Soils, Farm-Crops, and Agricultural Engineering (which became its own department in 1907). Today, the department teaches crop sciences and breeding, soil sciences, meteorology, agroecology, and biotechnology.

The Department of Agronomy was formed in 1902. From 1917 to 1935 it was known as the Department of Farm Crops and Soils.

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  • Department of Farm Crops and Soils (1917–1935)

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Soil ice content (θi) is an important property for many studies associated with cold regions. In situ quantification of θi with thermo-time domain reflectometry (TDR) at temperatures near the freezing point has been difficult. The objective of this study is to propose and test a new thermo-TDR approach to determine θi. First, the liquid water content (θl) of a partially frozen soil is determined from a TDR waveform. Next, a pulse of heat is applied through the thermo-TDR sensor to melt the ice in the partially frozen soil. Then, a second TDR waveform is obtained after melting to determine the θl, which is equivalent to the total water content (θt ) of the partially frozen soil. Finally, θi is calculated as the difference between θt and θl. The performance of the new approach was evaluated in sand and loam soils at a variety of θ t values. The new approach estimated θt , θl, and θi accurately. The root mean square errors (RMSE) of estimation were 0.013, 0.020, and 0.023 m3 m−3 for sand, and 0.041, 0.026, and 0.031 m3 m−3 for loam. These RMSE values are smaller than those reported in earlier thermo-TDR studies. Repeating the thermo-TDR measurements at the same location on the same soil sample caused decreased accuracy of estimated values, because of radial water transfer away from the heater tube of the thermo-TDR sensor. Further research is needed to determine if it is possible to obtain accurate repeated measurements. The use of a dielectric mixing model to convert the soil apparent dielectric constant to θl improved the accuracy of this approach. In our investigation, application of a small heat intensity until the partially frozen soil temperature became larger than about 1°C was favorable. The new method was shown to be suitable for estimating ice contents in soil at temperatures between 0°C and -2°C, and it could be combined with the volumetric heat capacity or thermal conductivity thermo-TDR based methods, which measured ice content at colder temperatures. Thus, the thermo-TDR technique could measure θi at all temperatures.


This is a manuscript of an article published as Kojima, Yuki, Yuta Nakano, Chihiro Kato, Kosuke Noborio, Kohji Kamiya, and Robert Horton. "A new thermo-time domain reflectometry approach to quantify soil ice content at temperatures near the freezing point." Cold Regions Science and Technology (2020): 103060. doi: 10.1016/j.coldregions.2020.103060.

Wed Jan 01 00:00:00 UTC 2020