Estimating soil profile volumetric water content using ground penetrating radar in southern slopes of Alborz Mountain

Ground penetrating radar (GPR) is a rapid and non-destructive technique that has been proposed for measuring soil water content (SWC) at intermediate scales from field scale to sub-watershed. The objectives of this study were: i) to test the capability of GPR technique for predicting profile of SWC at field scale, and ii) evaluate GPR techniques compared with both the laboratory measurements and time domain reflectometry (TDR) method to provide accurate SWC. Consequently, a GPR apparatus (Akulla 9000) equipped with 700 MHz antennas was used as a common-offset to collect the data at three soils texture classes (sandy loam, loam and silty loam). Volumetric soil water content was obtained from laboratory measurements of gravimetric soil moisture and dry bulk density. A hyperbolic curve was fitted to the radar gram to estimate the velocity and dielectric constant of GPR signals. The dielectric constant values were then feed to the experimental function suggested by Topp et al. (1980). Comparing the GPR and laboratory measurement results, the root mean square error (RMSE) and maximum error (ME) were equal to 3.32 and 5.8, respectively. Regarding to the TDR results, as the target values, the RMSE and ME values were equal to 2.4 and 5, respectively. The correlation coefficient between the GPR values and the laboratory measurements were 0.86. In conclusion, GPR method, due to a higher sampling density, could be used as a rapid, cost-effective and non-destructive technique to estimate profile of SWC at scales from fields to sub-watershed.