Experimental Studies for Monitoring Water-level by Dipole-antenna Array Radar Fixed

We propose a method for monitoring the movement of moving targets, such as water-level, at con-siderable depth, using dipole array-type radar with the dipoles fixed at various positions in the subsurface. We report on monitoring the water-level variation in a sand tank over several hours with the dipole-antenna array. A dipole-antenna with an optical modulator made of non-metallic mate-rial is used as the receiving antenna element. The antenna has little effect on the electromagnetic field being measured, and the optical modulator does not need electrical power. The basic idea of a radar system fixed in a subsurface is to distribute the dipole-antennae and to monitor the movement of a target, such as water distribution, over long periods of time, using scattered waves from the target. In order to demonstrate the validity of the radar system, we carried out laboratory experi-ments. We positioned several receiving dipole-antennae with the optical modulators, in a small package inside the sand. We raised the height of the water-level in the sand and measured waves scattered from the boundary between the saturated and unsaturated layers. We analysed the radar signals with the MUSIC algorithm utilizing Method of Moment analysis and monitored the 2D location of a moving scattering centre over several hours. By comparing the water-level in a vertica