Three-dimensional vadose zone hydrology based on high-density electrical resistivity tomography

Highdensity electrical resistivity tomography, which bases on the measurements of material resistivity, is one of the geophysical prospecting methods recently developed. With its convenient, fast and usable in multiscale advantages, the technique can be used to conduct noninvasive monitoring in threedimensions. Since the physical, chemical, biological and hydrological processes occurred in the vadose zone unavoidably would result in changes in the material resistivity, electrical resistivity tomography is helpful in understanding these processes. In this paper, first, the electrode array, measurement method and inversion algorithm for the method were introduced. Then, factors that affect the material resistivity were discussed. Finally, several applications that base on the spatial heterogeneity and temporal variations in resistivity were reviewed, including process monitor and parameter estimation in water pollution, unsaturated zone water flow, solute and heat transport, and material structure change under stress. Applications of the method in the performance evaluation of engineering projects were also introduced. By these reviews, we hope that the researches in threedimensional vadose zone hydrology could benefit from the electrical resistivity tomography well.