IR reflectance signatures, as measured for surface distributed particles, differ from absorbance spectra (found incommercial libraries) or those associated with reflectance from surfaces of bulk materials. Accordingly, analyte-particlesizes and morphology, as well as the influence of particle-substrate coupling, must be considered for development ofmodels and detection algorithms. This report describes preliminary results concerning modeling and measurement of IRreflectance signatures for micron-sized and irregularly-shaped particulates. Modeling is based on Mie scattering theory,combined with a model of particle-substrate interaction. The model inputs involve particle and substrate opticalconstants (complex index of refraction - n and k), particle size (diameter) distribution parameters, average areal massloading and substrate roughness. The modeling results are compared to empirical diffuse reflectance spectra (measuredby a benchtop FTIR spectrometer) as well as back-reflectance spectra (measured using our quantum cascade laser-basedfieldable standoff detection platform). This model is currently being used to generate large synthetic datasets fordetection algorithm testing and development purposes.
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