Non-destructive inspection of buildings using radar polarimetry

Natural disasters such as earthquakes often occur in Japan. Houses and buildings are broken due to earthquakes. It is difficult to know how much damage is caused inside a wall only by a visual observation. GB-SAR (Ground-Based Synthetic Aperture Radar) measurement is a way to measure the inside of a wall as a nondestructive inspection. By using GB-SAR, it can measure the inside without contacting a wall. In this study, imaging latticed rebars and damages inside a wall is an objective. For the study, a polarimetric radar system was built based on a vector network analyzer (VNA). Spiral antennas were used to achieve a wide frequency bandwidth. We carried out measurements with 2-dimentional scan. The scanning was repeated three times with different combinations of polarization, i.e., LL, RR, and LR. These radar data could image all the rebars. The measured data in the circular polarization basis are transformed to the linear polarization, i.e., HH, VV and HV. The obtained radar image in the HH polarization shows an only horizontally placed rebars and VV shows only vertical one.