Dual-band discrimination and imaging of plastic objects

Plastics are often used in mine and IEDs. Difficult to detect with traditional approaches, plastics are spectrally active in the shortwave and mid-infrared due to vibrational absorptions from the C-H bonds of which they are composed; bonds and vibrations that are diagnostic of and spectrally vary with composition. Hyperspectral infrared imaging has proven exceedingly capable of detecting and categorizing plastics. Here we pursue a dual-band imaging approach that leverages the ubiquitous presence of the ~1.7-micron harmonic of the ~3.4-micron fundamental absorption feature for a low SWaP (Size, Weight, and Power) instrument concept. The 1.7-micron band is also in a spectral region free of telluric and almost all geologic absorption features, making its presence in a reflectance spectrum almost a unique marker for plastics. We have developed and tested a two-camera, dual-band sensor, emphasizing imaging over spectroscopy and implementing on-camera processing to achieve near real-time, partially autonomous detection and imaging of plastic objects. The sensor has proven successful in discriminating and imaging plastics such as fiberglass, styrene, and acrylics from background materials such as grass, dirt, rocks, and brush. The sensor is challenged by certain plastics, especially thin, transparent plastics (less relevant to mines and IEDs) even if they are spectrally active near 1.7 microns. Also, photometric variations in the observing conditions can mask weak plastic signatures. We will discuss our current measurement and technical approach, the results and the challenges that remain to implementing an effective low SWaP sensor for the detection and imaging of plastic objects.