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Proceedings Paper

Gas-cell measurements for evaluating longwave-infrared passive-sensor performance
Author(s): Alan S. Cummings; Roger J. Combs; Mark J. Thomas; Timothy Curry; Robert T. Kroutil
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Paper 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 5oC to 50oC. 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.

Paper Details

Date Published: 25 October 2006
PDF: 22 pages
Proc. SPIE 6378, Chemical and Biological Sensors for Industrial and Environmental Monitoring II, 63780M (25 October 2006); doi: 10.1117/12.675961
Show Author Affiliations
Alan S. Cummings, Tetra Tech EM Inc. (United States)
Roger J. Combs, Research and Technology Consultants (United States)
Mark J. Thomas, U.S. EPA (United States)
Timothy Curry, U.S. EPA (United States)
Robert T. Kroutil, Los Alamos National Lab. (United States)

Published in SPIE Proceedings Vol. 6378:
Chemical and Biological Sensors for Industrial and Environmental Monitoring II
Steven D. Christesen; Arthur J. Sedlacek III; James B. Gillespie; Kenneth J. Ewing, Editor(s)

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