Imaging Fourier Transform Spectrometry of Combustion Events

The Telops, Inc., field-portable imaging radiometric spectrometer technology-midwave extended (FIRST-MWE) was characterized both spatially and spectrally, using blackbody sources in a climate-controlled laboratory environment. Individual pixel temperature variation of less than 0.5°C was demonstrated on a 32 × 32 pixel array while imaging a 3.5 in. blackbody at 65°C. A 150°C blackbody background source was imaged at a distance of 10 m with the FIRST-MWE set to a spectral resolution of 0.25 cm^-1 and a 128 × 128 pixel window. The corresponding spectral radiance was fitted to a line-by-line radiative transfer model (LBLRTM) of the scene based on the HITRAN (high-resolution transmission) database with a high degree of precision. Following demonstration of satisfactory instrument performance in both spatial and spectral domains, hyperspectral and high-speed broadband infrared (IR) imagery of a propane torch in front of a blackbody background were obtained with the FIRST-MWE in spectral mode and camera mode, respectively. Hyperspectral algorithms were employed to differentiate plume from non-plume pixels. Future work will improve this algorithm so that, with proper thresholding, plume pixels can be extracted from the remaining data set. This approach will result in a significant level of data reduction prior to implementing more computer-intensive chemical and temperature analysis on the plume hyperspectral datacube. Finally, exhaust from a diesel-fueled Turbine Technologies, Ltd. SR-30 turbojet engine was imaged with the FIRST-MWE from a side-plume vantage point during steady-state operation in both spectral and camera mode.