Experimental considerations for the proximate standoff detection of highly scattering hazardous materials using infrared techniques

Infrared spectroscopy is a powerful laboratory technique for detection of and discrimination between hazardous chemical threats, such as explosive materials, and non-hazardous background chemicals. Transitioning this method to the field however has significant challenges, especially when being deployed as a standoff, or proximate standoff technique. The main issue for proximate standoff detection lies in the ability of a system to collect enough reflected light from a source illuminating a surface to provide chemical information for the target material. This issue is further exacerbated when trying to detect highly scattering materials on surfaces, such as particulates or powders, which are typical forms for explosive materials. While diffuse reflectance from such materials provides good chemical vibrational absorption band information, when being collected at some distance away from the sample, this scattering provides a significant detection challenge. We present detection results for highly scattering inkjet printed explosive standards, collected at proximate standoff distances ( 0.5 m) in a laboratory environment. Discrimination between these standards using both conventional infrared spectroscopy, as well as NRL's unique optical filter based biomimetic sensing approach are discussed. This work is meant to inform the rational development of portable infrared optical sensors for detection of explosives at proximate distances in operational environments.