Di-Sense: In situ real-time permittivity estimation and soil moisture sensing using wireless underground communications

Internet of Underground Things (IOUT) communications have the potential for soil properties estimation and soil moisture monitoring. In this paper, a method has been developed for real-time in situ estimation of relative permittivity of soil, and soil moisture, that is determined from the propagation path loss, and velocity of wave propagation of an underground (UG) transmitter and receiver link in wireless underground communications (WUC). The permittivity and soil moisture estimation processes (Di-Sense, where Di- prefix means two) are modeled and validated through an outdoor UG software-defined radio (SDR) testbed, and indoor greenhouse testbed. SDR experiments are conducted in the frequency range of 100–500 MHz, using antennas buried at 10 cm, 20 cm, 30 cm, and 40 cm depths in different soils under different soil moisture levels, by using dipole antennas with over the air (OTA) resonant frequency of 433 MHz. Experiments are conducted in silt loam, silty clay loam, and sandy soils. By using Di-Sense approach, soil moisture and permittivity can be measured with high accuracy in 1–15 m distance range in plant root zone up to depth of 40 cm. The estimated soil parameters have less than 8% estimation error from the ground truth measurements and semi-empirical dielectric mixing models.