Mapping spatial variation in surface soil water content: comparison of ground-penetrating radar and time domain reflectometry

Abstract Mapping soil water content (SWC) is a difficult but important task in many fields, such as hydrology, agronomy and soil science. Ground-penetrating radar (GPR) is a valuable technique to measure surface SWC at an intermediate scale in between the scales of time domain reflectometry (TDR) and remotely sensed data. To measure SWC with GPR, the surface soil permittivity was determined with the ground wave velocity. The first aim of this study was to evaluate the potential of GPR to measure spatial SWC variation. The second aim was to compare GPR and TDR with respect to the type of spatial SWC structures that can be measured by these methods. A spatial structure in SWC was created by heterogeneous irrigation with sprinklers of various intensities. Then spatial SWC variation was measured with both GPR and TDR. The experiment showed that GPR is well able to measure spatial SWC variation as expressed by the variogram. The larger measurement volume of GPR filtered out small-scale spatial variation ( 5 m) in SWC. Especially the boundaries between areas with different SWC were better resolved in case of GPR because of the large number of GPR measurements obtained with the same measurement effort. Small-scale features (

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