14 August 2002 Two optical methods for vehicle tagging
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Optical tagging methods have the advantage that they cannot be detected by a suspicious criminal or terrorist using a radio frequency (RF) sensitive device to scan his vehicle for the presence of an RF emitting tag. We will describe two optical tagging methods in which the presence of the tagging marks can be visually discovered only by very close observation. On the other hand, the tags can be readily recognized by a surveillance team through the use of infrared imagers, either in the longwave infrared (LWIR) or in the near infrared (NIR). The first approach uses a clear coating that has a higher thermal emissivity than the glass window to which it is applied. This coating can be viewed with a thermal imager that operates in the LWIR, with the tags appearing as bright marks on a dark background. The second method uses an NIR laser illuminator and also quarter-wave thick layers applied to the license plate of a vehicle. When viewed with a polarization-sensitive imager that operates in the NIR, these quarter-wave tags appear as bright marks on a dark background. We will show sample images of both of these optical tags, as viewed in the LWIR and NIR regions, respectively.
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John K. Coulter, John K. Coulter, Christopher F. Klein, Christopher F. Klein, James C. Jafolla, James C. Jafolla, } "Two optical methods for vehicle tagging", Proc. SPIE 4708, Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Defense and Law Enforcement, (14 August 2002); doi: 10.1117/12.479327; https://doi.org/10.1117/12.479327

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