**6. GPR**

Ground penetrating radar (GPR) is a useful method for shallow geophysical exploration and is widely used for the detection of buried objects such as pipes and cables and voids under pavement. GPR basically has a pair of transmit and receive antennas. By scanning the GPR unit, GPR profiles along the survey line can be obtained. In order to extend the swath width in the direction perpendicular to the survey line, we can set multiple radar units and measure simultaneously. If the multiple radar devices are synchronized, it is a multi-static radar and can greatly improve the quality of radar data. And if we use all the combinations of the transmit and receive antennas, we can configurate MIMO GPR.
