title: Characterization of automotive paint by optical coherence tomography.
abstract: Automotive paint is common trace evidence that plays a significant role in many vehicle-related criminal cases. However, the conventional methods of obtaining tomographic images tend to damage the samples. Optical coherence tomography (OCT) is a novel method to obtain high-resolution and cross-sectional images of the automotive paints in a non-destructive, and high-speed manner. In this study, OCT was applied to image and analyze the automotive paint, using scanning electron microscope (SEM) as reference. Eight automotive paint samples of different brands were examined. The images of multi-layer structures provided by OCT system with 5μm depth resolution were consistent with those by SEM. To distinguish different paints with similar visual appearance, we extracted internal structural features from the images using peak analysis and optical attenuation fit. Six characterized parameters were found to distinguish the samples including the optical path length (OPL) of base coat, the optical attenuation coefficient (OAC) of base coat, the OPL of clear coat, the back-scattering ratio (BSR) of clear coat and base coat, the OPL of primer surfacer, and the BSR of base coat and primer. Statistical differences were evaluated by an independent t-test with p<0.05. OCT was applied to analyze repainted paint as well. Three-dimensional OCT reconstruction of the paints was also implemented to create en face (transverse section) images for morphology examination and comparison. These results suggest that OCT imaging can provide additional new features for analyzing the automotive paints and thereby may be a promising supplement to traditional methods. Meanwhile, the OCT system is favorable for achieving in-situ and real-time examination at the scene of crime.
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China. Electronic address: zhangning@cifs.gov.cn.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Low-dimensional Quantum Physics, Department of Physics, Tsinghua University and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Chengming
authors.initials: C
authors.lastname: Wang
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Zhenwen
authors.initials: Z
authors.lastname: Sun
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Hongcheng
authors.initials: H
authors.lastname: Mei
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Huang
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Xu
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Lanchi
authors.initials: L
authors.lastname: Xie
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Guo
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Yuwen
authors.initials: Y
authors.lastname: Yan
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Li
authors.affiliation: Institute of Forensic Science, Ministry of Public Security , Beijing 100038, China.
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Low-dimensional Quantum Physics, Department of Physics, Tsinghua University and Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Xue
authors.affiliation: College of Forensic Science, People's Public Security University of China, Beijing 100038, China.
authors.forename: Ningning
authors.initials: N
authors.lastname: Liu
keywords: Automotive paint; Forensic imaging; Optical Coherence Tomography; Trace evidence