Abstract

Many agricultural and hydrological processes require the detailed knowledge of soil water content (SWC) in the vertical profile. Quantifying real-time and in situ SWC is difficult due to time, cost, toil, and technical issues. This paper describes the development of a multi-depth SWC monitoring sensor which can estimate the SWC from 4 vertical depths simultaneously. The probe is a type of electromagnetic (EM) sensor that indirectly measures the SWC on the basis of dielectric theory. The sensor was calibrated with soil samples of three distinct topographical locations. The calibration models were established by fitting linear order equations. The performance of the sensor was evaluated in situ field conditions. A multi-depth SWC curve was investigated to examine the impact of continuous estimations of SWC at specified depths on the sensor performance. The sensor was integrated with vertical interpolation technique to improve the measurement accuracy. The results indicated the optimal range of the SWC measurements, and the estimation error was less than 5%, except irrigation cycles. The linear fit coefficient of determination (R²) ranged from 0.957 to 0.993 and root mean square error (RMSE) was ranging from 1.565 to 4.456. The results showed that the sensor performed consistently better for at least 4 months within acceptable soil conditions. The sensor will be advantageous for continuous estimations of SWC, and managing the irrigation practices.

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