Recovering hidden sub-layers of repainted automotive paint by 3D optical coherence tomography

In violent vehicular crimes, the damaged area of a vehicle is usually repainted artificially in order to conceal the evidence. Detecting and recovering the hidden sub-layer morphology of repainted automotive paint is highly valuable for providing trace evidence in hit-and-run cases. Optical coherence tomography (OCT) is a novel forensic imaging technique for repainted automotive paint analysis with the advantages of non-destructive, noncontact, high-resolution and cross-sectional imaging. In this study, we applied a custom-built spectral-domain OCT configuration with ~6 μm axial and lateral resolution to obtain three-dimensional (3D) images of an artificially prepared, internally-damaged, repainted automotive paint surface. Two-dimensional (2D) cross-sectional images were produced to locate the damaged area and 3D-OCT reconstruction was performed to directly visualize the sub-layers beneath the repainted paint surface. The results demonstrate that 3D-OCT technology manages to recover high-resolution sub-layer images of the repainted automotive paint through volumetric imaging, and thus provides more valuable information for forensic purposes.