Remote identification of chemicals concealed behind clothing using near infrared spectroscopy

Abstract

Measurements are presented which demonstrate that near infrared (NIR) spectroscopy can be used to identify chemicals concealed behind clothing. This has been achieved for detector stand-off distances of 3 m. The optical properties of a range of clothing materials have been investigated, and the transmission of NIR signals found to be sufficient for spectroscopy. The study has shown that granular solid materials can be identified when hidden behind a layer of clothing. Examples of chemicals used in this study include ammonium nitrate and other ammonium salts. Details of the current measurements and results are given, together with suggestions for increasing detection sensitivity.