Simultaneous multichannel multi‐offset ground‐penetrating radar measurements for soil characterization

For vadose zone studies, it is essential to characterize the soil heterogeneity. However, manual soil coring is time consuming and lacks spatial coverage. Ground‐penetrating radar (GPR) has a high potential to map these parameters. However, with conventional common‐offset profile (COP) measurements, soil layer changes are only detected as a function of time, and no exact determination of velocities, and thus permittivity, is possible. For velocity estimation, time‐consuming point‐scale common midpoint (CMP) or wide‐angle reflection and refraction (WARR) measurements are necessary. Recently, a novel simultaneous multi‐offset multichannel (SiMoc) GPR system was released, enabling rapid profiling with virtually continuous acquisition of WARR gathers. For this system, we developed a new processing approach. First, time shifts caused by the different cables and receivers were eliminated by a novel calibration method. In the obtained CMP gathers, groundwave and (when present) reflection velocities were determined with an automated semblance approach. The obtained velocity can be converted to permittivity and soil water content. We tested SiMoc GPR with a synthetic study and time‐lapse field measurements. In the synthetic study, the accuracy of velocity and layer thickness were within 0.02 m ns−1 and 2 cm. The SiMoc field results (spatial sampling of 5 cm) are consistent with coarse sampled single‐channel data (spatial sampling of 10 m). Soil water content changes over the different measurement days were in agreement with nearby installed sensors (one per hectare). Overall, SiMoc GPR is a powerful tool for fast imaging of spatially highly resolved permittivity, and soil water content at a large scale.