The Ground Penetrating Radar(GPR) is a typical non-destructive test equipment which is widely used in seeking a cavity or underground facility. Test results are generally expressed 2D monochrome or color images, distribution of the parabolic waveforms are used to determine the existence of cavity and facility. (Fig. 1) But, an analysis method of image may cause errors depending on the knowledge and experience of analyst. In this study, we analyzed the coefficient of correlation between A-Scan data of GPR to judge the existence of cavity located under the pavement layer. The correlation analysis was performed based on the assumption that the relationship of correlation between a number of A-Scan data passing through a non-cavity section is larger than a small number of A-Scan data passing through a cavity section, and relationship of correlation was visualized using Surfer Program. (Fig. 2) In addition, apart from the correlation analysis, we compared the Power spectrum of the A-scan data for the cavity section and non-cavity section. In other words, assuming that the size of the energy changes depending on the existence of the cavity, PSD (Power Spectrum Density) is obtained for all the B-Scan data, and the tendency of the energy size is confirmed using the 3D wireframe map of the Surfer program. (Fig. 3) As a result, the correlation coefficient shows a small tendency in the cavity section and the PSD shows a large tendency, which is intuitively recognized that the energy attenuation in the cavity section is smaller than other material. But, there are some ambiguous sections to judge the tendency clearly, this is estimated to be noise on the underground facility and it is necessary to take measure of mitigating this.

• Sang-yum Lee(Department of Construction Information, Induk University)
• Jung-moo Kim(Department of Construction Information, Induk University)
• Dae-yeol Kwak(Department of Construction Information, Induk University)