Experimental detection of the volume of the drip irrigation soil wetted body using Ground Penetrating Radar

Abstract

The accurate detection of the volume of the soil wetted body (SWB) is the theoretical basis for the optimal design of a drip irrigation system. In view of the shortcomings of traditional detection methods, such as low efficiency, high cost, and poor in situ detection, this paper explores the rapid, in situ, and nondestructive estimation techniques of SWB volume using Ground Penetrating Radar (GPR). Through drip irrigation of different water volumes and geotechnical experiments, the SWBs with different sizes were formed in air-dried soil and natural soil, respectively. The GPR scan lines on the ground were arranged to obtain the SWB radargram, and the profile shape of the wetted body was restored by the F-K transformation process (frequency-wave domain migration algorithm) that can transform the wave equation in the time-space domain into the frequency-wavenumber domain to achieve offset homing. On this basis, the SWB volume estimation model was constructed by three methods: regression analysis, geometric calculation, and profile triple integration (profile area accumulation). Additionally, the accuracies of the models were verified by the measured data of the SWB excavation. For each of these methodologies, we illustrate the quality of the output with the measured data and discuss the possibilities and limitations. The results show that the profile triple integration model is not accurate. The regression analysis model has the greatest accuracy. However, owing to the difference in soil characteristics, the model input parameters must be changed. Relatively, the geometric calculation model is the best model to detect the SWB volume. From the results, we can draw a conclusion that the method combining F-K transformation process and the geometric calculation model can accurately measure the volume of SWB, and it has better adaptability in different soils. We demonstrate the GPR as a rapid geophysical tool that can be used successfully to explore the volume of the SWB formed under drip irrigation. This study expands the agricultural application of GPR and provides a new method for in situ nondestructive rapid detections of the SWB volume.