Inverse spectral analysis of spectrum-feature-enhanced diffuse reflectance measured using infrared backscatter imaging spectroscopy

Abstract

This report describes inverse spectral analysis of diffuse-reflectance spectra measured using Infrared Backscatter Imaging spectroscopy (IBIS). In IBIS, a tunable infrared laser illuminates a target while an infrared camera detects the backscatter. Target analytes are identified by analyzing the pattern of absorption dips in the detected backscatter and comparing them to the known or simulated reflectance spectra of hazardous materials. The backscatter spectrum is comparable to diffuse reflectance measured using a Fourier transform infrared (FTIR) spectrometer. The analysis methodology applied here entails iterative adjustment of spectra using phenomenological backgrounds. and estimation of absorbance using the Kubelka-Munk (KM) theory of diffuse reflectance. Applying spectrum-feature enhancement, measured with a field spectrometer, can provide a better estimation of dielectric response, which is for comparison to reference dielectric functions, for identification of target materials.