[A-GE30] Subsurface Mass Transport and Environmental Assessment

[AGE30-P03] A new sensor that simultaneously determines soil temperature, water content, electrical conductivity, and matric potential

*Yuki Kojima¹, Manabu Matsuoka¹ (1.Department of Civil Engineering, Gifu University)

Keywords:soil moisture content, soil matric potential, soil electrical conductivity, soil temperature, time domain transmissiometry

Quantifying in-situ soil properties with sensors is essential for understanding mass and energy transport in subsurface soil. In this study, we aimed to develop a new time domain transmissiometry (TDT)-based sensor to simultaneously determine soil temperature, water content, electrical conductivity, and matric potential with a single probe, and to evaluate its performance. TDT is a technique to measure soil dielectric permittivity, which is strongly correlated with soil water content, and electrical conductivity by electromagnetic pulse propagating two parallel guide rods. The newly developed sensor determines soil water content and electrical conductivity with TDT, and soil matric potential by measuring the electrical capacity of a porous medium embedded on the sensor probe. Soil temperature is measured with a thermistor embedded in the sensor circuit. A series of laboratory experiments were performed to obtain the relationships between soil properties and sensor outputs. In addition, the temperature dependence of the sensor outputs was evaluated. A field experiment was performed to evaluate the sensor performance in a natural environment. The results of laboratory experiments showed that the outputs of the new sensor are strongly correlated to the soil properties, and models to convert the sensor outputs to soil properties were developed. The new sensor could measure soil water content with 5% accuracy and matric potential ranging between -100 and -10 kPa. Electrical conductivity measurements also had high reliability. The new sensor was not susceptible to temperature except for the dry range of matric potential. The field experiment showed that the new sensor could capture the soil temperature, water content, matric potential, and electrical conductivity dynamics due to solar radiation, precipitation, and daily evaporation well. The sensor could stably operate for a long period. In addition, It was found that the new sensor has the ability to produce in-situ soil water retention curves. The new sensor can contribute to various subsurface soil mass and energy transport studies.