In recent years, the demand for ground penetrating radar（GPR）technology has increased in the cavity exploration along with the market expansion of the maintenance field in the underground of the road, the port facilities and the river embankment.

However, when the GPR is compared with the other geophysical explorations, the GPR obtains the high resolution result although the application is only to the cavity exploration and geological survey of the near surface in the current status. On the other hand, it is impossible to detect a detailed structure of the near surface by the seismic exploration and electrical prospecting although the applied depth is over 10m depth because their resolution is several meters. Therefore it is a problem to extend the penetration depth of GPR with high resolution.

We have developed a new GPR technique applying to a chirp signal to extend the penetration depth and to maintain the resolution. We conducted the experiment for buried pipe, the cavity and geological structure detection by the chirp radar to enhance the GPR.

As a result, we confirmed the 5 meters penetration depth without impairing the resolution and operability of the GPR. The developed chirp radar is able to extend the depth of penetration while maintaining high resolution.