KEYWORDS: Calibration, Absorption, Spectral calibration, Apodization, Black bodies, Signal to noise ratio, Instrument modeling, Temperature metrology, Staring arrays, Fourier transforms
The Telops Hyper-Cam midwave (InSb 1.5-5.μm) imaging Fourier-transform spectrometer observed the plume from a coal-burning power plant smokestack. From a distance of 600 meters, the plume was captured on a 128×64 pixel sub-window of the focal-plane array with each pixel imaging a 19.5×19.5cm2 region. Asymmetric interferograms were collected with long side and short side maximal optical path differences of 2.4cm and 0.9cm, respectively. Interferograms were recorded for each scan direction. The plume was strongly emissive across 1800-3000cm-1, and raw spectra revealed emissions from CO2, CO, H2O, NO, SO2, and HCl. A complete description of the instrument calibration and lineshape modeling is presented, including a simple and computationally efficient method of averaging spectra from forward- and reverse-scan interferograms that avoids the need to model a complex instrument lineshape. A simple radiative
transfer model is developed to interpret the spectrum between 2565 ≤ ~ν ≤ 3000cm-1. Examination of the HCl spectrum demonstrates exceptional agreement between the data and an ideal instrument lineshape. For a pixel immediately above the stack exit, the plume temperature is estimated to be 399.6±0.6K with an SO2 concentration of 376±10ppmv, and these values agree well with in situ measurements of 407.0±0.2K and 383±2ppmv, respectively.
A midwave infrared (MWIR) imaging Fourier transform spectrometer (FTS), the Telops FIRST-MWE (Field-portable
Imaging Radiometric Spectrometer Technology - Midwave Extended) has been utilized for the standoff detection and
characterization of chemical plumes. Successful collection and analysis of MWIR hyperspectral imagery of jet engine
exhaust has allowed us to produce spatial profiles of both temperature and chemical constituent concentrations of
exhaust plumes. Successful characterization of this high temperature combustion event has led to the collection and
analysis of hyperspectral imagery of lower temperature emissions from industrial smokestacks. This paper presents
MWIR data from remote collection of hyperspectral imagery of methyl salicilate (MeS), a chemical warfare agent
simulant, during the Chemical Biological Distributed Early Warning System (CBDEWS) test at Dugway Proving
Grounds, UT in 2008. The data did not contain spectral lines associated with emission of MeS. However, a few broad
spectral features were present in the background-subtracted plume spectra. Further analysis will be required to assign
these features, and determine the utility of MWIR hyperspectral imagery for analysis of chemical warfare agent plumes.
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