Instrument calibration and lineshape modeling for ultraspectralimagery measurements of industrial smokestack emissions

摘要

The Telops Hyper-Cam midwave (InSb 1.5-5.5μm) imaging Fourier-transform spectrometer observed the plume froma coal-burning power plant smokestack. From a distance of 600 meters, the plume was captured on a 128 x 64 pixelsub-window of the focal-plane array with each pixel imaging a 19.5 × 19.5 cm~2 region. Asymmetric interferograms werecollected with long side and short side maximal optical path differences of 2.4 cm and 0.9 cm, respectively. Interferogramswere recorded for each scan direction. The plume was strongly emissive across 1800-3000 cm~(-1), and raw spectra revealedemissions from CO_2, CO, H_2O, NO, SO_2, and HCl. A complete description of the instrument calibration and lineshapemodeling 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 radiativetransfer model is developed to interpret the spectrum between 2565 < V < 3000 cm~(-1). Examination of the HCl spectrumdemonstrates exceptional agreement between the data and an ideal instrument lineshape. For a pixel immediatelyabove the stack exit, the plume temperature is estimated to be 399.6 ±0.6 K with an SO_2concentration of 376 ± 10 ppm,and these values agree well with in situ measurements of 407.0 0.2 K and 383 ± 2 ppm_v, respectively.