Gas-cell measurements for evaluating longwave-infrared passive-sensor performance

Alan S. Cummings; Roger J. Combs; Mark J. Thomas; Timothy Curry; Robert T. Kroutil

doi:10.1117/12.675961

25 October 2006 Gas-cell measurements for evaluating longwave-infrared passive-sensor performance

Alan S. Cummings, Roger J. Combs, Mark J. Thomas, Timothy Curry, Robert T. Kroutil

Proceedings Volume 6378, Chemical and Biological Sensors for Industrial and Environmental Monitoring II; 63780M (2006) https://doi.org/10.1117/12.675961
Event: Optics East 2006, 2006, Boston, Massachusetts, United States

Abstract

A longwave-infrared (LWIR) passive-spectrometer performance was evaluated with a short-pathlength gas cell. This cell was accurately positioned between the sensor and a NIST-traceable blackbody radiance source. Cell contents were varied over the Beer's Law absorbance range from the limit of detection to saturation for the gas analytes of sulfur hexafluoride and hexafluoroethane. The spectral impact of saturation on infrared absorbance was demonstrated for the passive sensor configuration. The gas-cell contents for all concentration-pathlength products was monitored with an active traditional-laboratory Fourier Transform Infrared (FTIR) spectrometer and was verified by comparison with the established PNNL/DOE vapor-phase infrared (IR) spectral database. For the passive FTIR measurements, the blackbody source employed a range of background temperatures from 5^oC to 50^oC. The passive measurements without the presence of a gas cell permitted a determination of the noise equivalent spectral noise (NESR) for each set of passive gas-cell measurements. In addition, the no-cell condition allowed the evaluation of the effect of gas cell window materials of low density poly(ethylene), potassium chloride, potassium bromide, and zinc selenide. The components of gas cell, different window materials, temperature differentials, and absorbances of target-analyte gases supplied the means of evaluating the LWIR performance of a passive FTIR spectrometer. The various LWIR-passive measurements were found to simulate those often encountered in open-air scenarios important to both industrial and environmental monitoring applications.

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Alan S. Cummings, Roger J. Combs, Mark J. Thomas, Timothy Curry, and Robert T. Kroutil "Gas-cell measurements for evaluating longwave-infrared passive-sensor performance", Proc. SPIE 6378, Chemical and Biological Sensors for Industrial and Environmental Monitoring II, 63780M (25 October 2006); https://doi.org/10.1117/12.675961

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KEYWORDS

Absorbance

Chlorine

Spectroscopy

FT-IR spectroscopy

Black bodies

Long wavelength infrared

Interferometers

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