Determination Method Of The Optimal Antenna Separation For Soil Moisture Monitoring Based On Ground Penetrating Radar

Accurate measurement of soil moisture content in the field is of great significance for crop growth monitoring and refined agricultural production management.At present,there are many methods and technologies for measuring soil water content,such as point-based soil moisture sensors and satellite remote sensing based on large areas,but there are still some interval scales between the point scale and the large regional scale,such as the need for rapid,accurate and non-destructive quantitative depth soil moisture monitoring based on the field scale of small farmland.As a new method for measuring soil water content,ground penetrating radar method can detect deep underground soil moisture content information while ensuring the accuracy of in-situ determination,and has the advantages of high work efficiency and no destructive effect on soil.The ground penetrating radar method has the application potential of soil moisture monitoring at the field scale,but there are many influencing variables such as radar frequency,antenna separation,soil depth and soil structure in the measurement accuracy,and the research basis of the quantitative depth of soil moisture at the field scale based on ground penetrating radar is relatively weak,among which,there are relatively few research literature on the quantitative relationship between different soil depths corresponding to the optimal antenna separation,and the relevant technical parameters need to be further studied and verified.This article conducts experimental research on the quantitative relationship between soil depth and optimal antenna separation in the process of rapid and accurate inversion of soil moisture content at the field scale.In the selected field area,a ground penetrating radar with a center frequency of 1000 MHz was selected.The method of Fixed Offset(FO)was used to measure10 antenna separations of different lengths between 0.2m and 2m in sequence.The reflected radar wave information of different depths of soil layers was obtained,and the soil dielectric constant was calculated.The soil volume water content was calculated using the Roth physical model formula.Select representative monitoring points to sample soil layers at different depths,and use the soil volume moisture content obtained by the drying method as the measured value.Analyze the accuracy of the soil moisture inversion value of the ground penetrating radar,and then determine the optimal antenna separation for inverting soil moisture content at different depths.The research conclusion is as follows:(1)The accuracy analysis of soil moisture content inversion using ground penetrating radar with different antenna separation shows that the optimal inversion depth is 10 cm when the antenna separation is 0.2m;When the antenna separation is 0.4m and 0.6m,the optimal inversion depth is20cm;When the antenna separation is 0.8m and 1.0m,the optimal inversion depth is 30cm;The optimal inversion depth for antenna separation of 1.2m and 1.4m is 40cm;The optimal inversion depth is 50 cm when the antenna separation is 1.6m;The optimal inversion depth for antenna separation of 1.8m and 2.0m is 60 cm.(2)The accuracy analysis results of ground penetrating radar inversion of soil water content at different depths show that The optimal antenna separation for soil moisture content in the 0-10 cm depth range was 0.2m,the optimal antenna separation for soil moisture content in the 0-20 cm depth range was 0.6m,the optimal antenna separation for soil moisture content in the 0-30 cm depth range was 1.0m,the optimal antenna separation for soil moisture content in the inverted0-40 cm depth range was 1.4m,and the optimal antenna separation for inverting soil moisture content in the 0-50 cm and 0-60 cm depth ranges was 1.8m.(3)The optimal inversion depth of 1000 MHz ground penetrating radar is 50 cm,and 1000 MHz ground penetrating radar is not suitable for inverting the water content of surface soil in the field(depth range is 0-10cm).(4)This article determines the optimal antenna separation for ground penetrating radar(GPR)inversion of soil moisture at different depths,providing a reference basis for antenna separation selection in future GPR soil moisture measurement applications,and providing a research foundation for the design and development of new soil moisture sensor prototypes in the next step.