Methods of Personnel Screening for Concealed Contraband Detection by Millimeter-wave Radiometric Imaging

摘要

The currently emerging terrorism and violence crimes in the scope of worldwide have posed increasingly extensive threats to the personnel and public security. Therefore, it is crucial to carry out personnel screening in the areas of airports, subways, customs and critical infrastructure, in order to detect contraband concealed underneath a person's clothing, such as guns, plastic explosives and drugs. With the advances in millimeter-wave (MMW) technology, MMW radiometric imaging has attracted an increasing interest in the application of security screening. Both the high transparency of clothing at millimeter wavelengths and the spatial resolution required to generate adequate images combine to make MMW radiometric imaging a natural approach of personnel screening for concealed contraband detection. On the basis of the principle of MMW radiometric imaging for applications of concealed contraband detection, a brief overview of some representative applied systems from abroad is given in this paper, according to the categories of different imaging mechanisms. Then, a series of researches on MMW radiometric imaging for personnel screening carried out at MMW Applied Laboratory of Nanjing University of Science and Technology are described in detail from different aspects. These researches mainly focus on the improved radiometer uncertainty equation of planar scanning imaging system, the motion-blur parameters identification of MMW radiometric images and the radiometric image fusion involving concealed contraband detection. Moreover, when the MMW radiometric imaging is carried out indoors, the benefit of the sky illumination no longer exists and the radiometric temperature contrast between the targets and the background decreases sharply, which results in the degradation of MMW radiometric images. Hence, the method of noise illumination is adopted in the application of indoor radiometric imaging. Ultimately, the development trends of MMW radiometric imaging with respect to personnel screening for concealed contraband detection is summarized.