A 16-channel, cross-reactive remote infrared chemical sensor for detection of toxic industrial chemicals in fixed-location applications is being developed. The outputs of the 16 channels, uncooled pyroelectric detectors fitted with infrared bandpass filters, can be viewed as a coarse spectrum of the chemical(s) in the field of view. This spectrum must be unmixed, wherein the identity and optical depth of the chemical(s) are estimated by processing the spectrum with a library of known signatures for the chemical(s) of interest.
Several unmixing methods are presented, including enhancements to linear projection methods, parameterization (curve fitting) of the system response, and non-linear, iterative techniques. It is found that linear methods and simple curve parameterizations produce excessive unmixing errors. Higher-order parameterization and iterative methods provide much better estimates, with the latter being more computationally intensive. The suitability of the methods for the application at hand is discussed.