An experimental study of calibration of soil moisture content by using the frequency domain reflectometry

Long-term and continuous monitoring of soil moisture content in a landslide body is important for the analysis and safety warning of landslides. Based on the frequency domain reflectometry (FDR), the principle of measuring soil moisture content is described in this paper. In order to improve the accuracy of soil water content measured by the FDR method, the soil moisture content of the landslides near the Jietai Temple is calibrated by the combination of indoor and field calibration methods, respectively. By comparing and analyzing the data of soil moisture measured by the FDR method and drying method, the corresponding relationship between the voltage signal, water content, absolute error and relative error is discussed, and a function model is established. The test results show that the soil moisture content measured by the FDR method is higher than that of the drying method. Through fitting and regression analyses of the test data with linear, multiple power curves and exponential forms, the four power curve is determined as the calibration method. The accuracy of soil moisture content measured after calibration is obviously improved, and the mean absolute error can be controlled within 2%. The calibration curve can be applied to the determination of soil moisture content with the FDR method in the landslide near the Jietai Temple and other similar areas.