Evaluation of Several Dielectric Mixing Models for Estimating Soil Moisture Content in Sand, Loam and Clay Soils
2003
As part of a NOAA-funded project, studies are being conducted at the University of
Puerto Rico-Mayaguez Campus using surface-based ground penetrating radar (GPR) to
measure soil moisture content. The GPR will eventually be used to verify values of soil
moisture at several locations in Puerto Rico using active radar and passive satellite-based
sensors. As a part of the estimation process, it is necessary to relate moisture content to the
GPR-measured dielectric constant. The motivation for this study was the need to select an
appropriate dielectric mixing model for the wide range of soils being considered in the study. An
important requirement of the dielectric mixing model was that it works well with input data
available from NRCS Soil Survey Reports (e.g., soil texture, available water capacity, etc). The
advantage of using this type of data is that it can be readily incorporated into a geographic
information system (GIS) to be used with the geo-referenced dielectric data of the surface and
satellite-based sensors.
This paper provides a review of several dielectric mixing models, and compares
moisture content estimates for sand, loam and clay soils, based on dielectric data
obtained from a GPR, TDR and Theta Probe™. These results are also compared to
soil moisture contents obtained from gravimetric data. Soils were characterized in
terms of their chemical and physical properties; information needed by several of the
dielectric mixing models. In some cases, especially with the loam soil, wide variations
in the dielectric constants and moisture contents were observed.
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