Study on the relationship between depth of asphalt pavement cavity defect and GPR antenna transceiver distance based on SSIM-S

The forward modeling of ground penetrating radar (GPR) is one of the core topics of road non-destructive testing. The relationship between antenna transceiver distance and cavity defect depth is of great significance to reveal features of radar signals. This paper conducted forward modeling of cavity defects in asphalt pavements based on the FDTD method. The cavity defects were filled with air. The simulated radar frequency was 400 MHz. The boundary conditions related to FDTD were determined. A total of 360 forward models of the experimental group and the control group were established. A new evaluation index SSIM-S (Structural similarity − Spearman rank order correlation coefficient) was proposed to characterize the relationship between different antenna transceiver distance and different cavity defect depth. The results indicate that a higher SSIM-S value corresponds to more pronounced features of cavity defect radar signals in the images. When the antenna transceiver distance is less than 25 cm, SSIM-S shows a positive correlation with cavity defect depth and a negative correlation with antenna transceiver distance. As the cavity defect depth increases, its influence by antenna transceiver distance decreases. Considering data volume and other practical detection issues, an antenna transceiver distance between 10 cm and 20 cm is optimal.