Infrared Reflectance Characterization of Ammonium Nitrate Residue on Roughened Aluminum for Potential Bioinspired Stand-off Sensor

摘要

Detection of explosives on surfaces could potentially be achieved using handheld standoff optical sensors, providing rapidintelligence and safety to the warfighter or first responder. Recent work has shown the capability to discriminate variouschemical vapors using a bioinspired or biomimetic detection system modeled on human color vision. This biomimeticsystem utilizes three overlapping broadband infrared optical filters to discriminate between various chemicals. Preliminaryreflectance data of chemicals on surfaces indicate a capability for discrimination of target chemicals and interferents byanalysis of biomimetic sensor output using novel analytical methods such as “Comparative Discrimination SpectralDetection” (CDSD). Transitioning this detection method to threats on surfaces at proximate standoff distances (~1 m)requires additional considerations including surface characteristics and angle of detection. This work explores sensordetection parameters for ammonium nitrate residue on aluminum surfaces of various roughnesses. Samples of theexplosives component ammonium nitrate, NH4NO3, diluted at 10%, 5%, and 1% in DI water, were prepared by dropcastingonto aluminum coupons with four surface finishes: polished, brushed, extruded, and sandblasted. Surface roughnesseswere measured. Single beam reflectance spectra (2 – 20 μm) were collected using a FTIR spectrometer over multipleindependent angles of incidence and collection (15° - 80°). Multiple factors were analyzed including albedo, and potentialsensor configurations. Characteristics for future MWIR and LWIR sensors, such as illumination power and detectorsensitivity, are evaluated which enable chemical spectral identification across range of aluminum surface roughness forproximate standoff distances and different angles of incidence.