ABSTRACT

Cross-hole borehole radar is being used for high-resolution characterization of subsurface structure. We conducted fundamental research of borehole radar which includes parallel measurement and fixed transmitter measurement at Tohoku University. Cross-hole radar is an efficient tool for characterization structure due to the sensitivity of water content in soil and rock. We concentrated first arrival time of direct wave and refracted wave in both methods. The first arrival time indicated velocity changes which depend on electromagnetic properties of a different soil layer. We figured out simulated travel times that indicate an arrival time in an ideal layer at each fixed transmitter measurement. Then, we tried to fit the measurement data to the simulated travel time. In high attenuation media, signal to noise ratio was much lower than low attenuation media. The simulated travel time did not fit radar cross sections due to the variation of velocity. As to separating point of the simulated travel time and measurement data, we could define an interface between two layers. The slope of refracted signals depended on a velocity of refraction layer. We overlapped the radar data and the simulated travel time of the refracted signal. The fixed transmitter measurements illustrated the variation of velocity along a vertical and horizontal direction. The simulated travel time assisted to calculate a velocity with high accuracy. As the result of parallel measurement, we could get signal at horizontal intervals. The amplitude of the first arrival signals was quite different in some intervals. Then, we calculated the dielectric permittivity and the volumetric water content using the empirical model for each particular layer.

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