Determination of liquid water in frozen soil using dielectric techniques: effects on temperature, ice and measurement frequency

Authors: Seyfried, Mark

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2004
Publication Date: 3/20/2004
Citation: Seyfried, Mark, 2004. Determination of liquid water in frozen soil using dielectric techniques: Effects of temperature, ice and measurement frequency, American Geophysical Union, Eos Trans. v.17, pp 85.

Interpretive Summary:

Technical Abstract: It is well established that ice and liquid water may coexist in soils over a wide temperature range. The proportions of ice and liquid water impact energy balance due to the heat of fusion. Other physical and chemical processes, such as infiltration and nutrient mineralization, are also strongly affected by the freezing process. Extensive research with time domain reflectometry (TDR) has shown that the TDR-measured apparent dielectric permittivity (Ka) is strongly correlated with the liquid water content in frozen soil. TDR is the most extensively studied and applied technique, but results of that research apply, to some extent, to other dielectric-based measurements such as capacitance probes, ground penetrating radar and synthetic aperture radar that are currently in use. Accurate measurement of liquid water depends on assigning an appropriate Ka-water content relationship or calibration. Most field applications rely on laboratory calibrations derived for unfrozen soils. This approach implicitly assumes that: (i) ice and air effects on Ka are equivalent and (ii) that changes in temperature do not affect the calibration. Neither is strictly true. We show that the impact of these assumptions on measurement accuracy is strongly dependent on soil properties and that, in some cases, resultant errors may be substantial. We then describe some approaches, such as the use of mixing model calibration equations or cool temperature calibrations, that may minimize these problems. These effects are also related to measurement frequency, which must also be considered when applying other (not TDR) dielectric techniques to liquid water measurement.