Horizontally Elongated Time Domain Reflectometry System for Evaluation of Soil Moisture Distribution.

Area of Science:

• Geotechnical Engineering
• Environmental Science
• Soil Physics

Background:

• Accurate soil water content (SWC) assessment is crucial for various environmental and agricultural applications.
• Traditional methods often struggle with nonuniformly wetted soils, leading to inaccurate estimations.
• Time Domain Reflectometry (TDR) is a common technique, but its application in heterogeneous soil conditions requires further development.

Purpose of the Study:

• To develop and validate a Horizontally Elongated Time Domain Reflectometry (HETDR) system.
• To evaluate the HETDR system's capability in assessing SWC in nonuniformly wetted soil samples.
• To compare the performance of HETDR with conventional vertical TDR probes.

Main Methods:

• Designed and constructed an HETDR probe with a specific three-rod configuration connected to a coaxial cable.
• Utilized a segmented acrylic container to create controlled nonuniformly wetted soil specimens.
• Placed the HETDR probe horizontally within the soil specimens and a conventional TDR probe vertically.
• Analyzed the relationship between signal amplitude, duration, and SWC in different soil segments.

Main Results:

• Observed an inverse relationship between average signal amplitude and SWC; higher SWC correlated with lower amplitude.
• Found a positive correlation between signal duration and SWC; increased duration indicated higher SWC.
• Demonstrated that estimated SWC generally increased with measured SWC.
• Highlighted significant accuracy in estimating segment length with HETDR, particularly under dry soil conditions.

Conclusions:

• The developed HETDR system is a viable tool for evaluating SWC in nonuniformly wetted soils.
• HETDR offers a promising approach for field-based measurements of average soil water content.
• The system shows particular strength in characterizing water content under drier soil conditions, improving upon existing methods.