A pipeline robot system for monitoring soil water content distribution

•Design a new pipeline robot system for monitoring soil water content distribution.•The robot system performs stable for horizontal and vertical mobile measurements.•The system extends measurement distance and improves positioning accuracy of robot.•The system is feasible for vertically and horizontally monitoring SWC dynamics. Monitoring soil water content (SWC) distribution is crucial for better understanding soil water dynamics and accurate hydrological modeling. In this study, a pipeline robot system for monitoring SWC distribution is designed to improve the current technical problems of insufficient measurement distance and low positioning accuracy of the existing SWC monitoring platform. The system consists of a pipeline robot, a fixed base station and a PVC pipe. The robot could fit into a 55-mm-diameter PVC pipe to measure SWC distribution horizontally, vertically, or at any angle to the horizontal direction. The base station serves as a data collector and also supplies power and distance information for recharging and positioning the robot, respectively. A series of tests for evaluating the performance of the pipeline robot system were conducted. Field experiments were also conducted to monitor soil water infiltration and horizontal distribution of SWC of crop root zone at three plots. The results showed that the minimum radius of volume of sensitivity of the dielectric sensor is about 2.25 cm. The robot for mobile measurement performed stable both in horizontal and vertical directions and the response of the dielectric sensor output to different dielectric materials is significant. The accumulated error of the encoder is effectively decreased from 4.3% to 1.2% by correcting the position error using the laser ranging sensor. The measured SWCs during the calibration experiment were highly correlated with those obtained by the drying method (R2 = 0.990 and RMSE = 0.0181 cm3 cm−3). The results of the field experiments demonstrated that the system is feasible for monitoring soil water infiltration in the vertical direction and SWC distributions of crop root zone horizontally at the three plots, indicating that the potential application of the developed system for long-term monitoring of SWC distribution under field conditions in the near future.