Experimental studies for monitoring water distribution by e-field sensor array type radar fixed in underground

We propose a method to monitor movement of some moving targets such as water distribution in deep depth with dipole array-type radar, which are varied and fixed in underground. In this paper, we report on monitoring water level movement in a sand tank for several hours with the dipole antenna array. The dipole antenna sensor with the optical modulator is made of non-metallic material except for the antenna itself. Therefore the antenna has little effect on the electromagnetic field being measured. A basic idea of the radar fixed in underground is to distribute the dipole antennas as receivers for long period, and monitor movement of some targets such as water distribution. In order to verify the radar system, we carried out laboratory experiments. We distributed four receiving dipole antennas using the optical modulators inside the sand, and fixed them. We increased height of the water level in the sand tank, and we measured reflected waves from a boundary between a saturated and an unsaturated layer with the antennas. We analyzed the radar signals, and tried monitoring 2- D estimation of a scattering center, which moves for several hours. We found that we could track a water level position for several hours by the radar in 2-D space.