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Proceedings Paper

Open-path FTIR data reduction algorithm with atmospheric absorption corrections: the NONLIN code
Author(s): William Phillips; George M. Russwurm
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Paper Abstract

This paper describes the progress made to date in developing, testing, and refining a data reduction computer code, NONLIN, that alleviates many of the difficulties experienced in the analysis of open path FTIR data. Among the problems that currently effect FTIR open path data quality are: the inability to obtain a true I degree or background, spectral interferences of atmospheric gases such as water vapor and carbon dioxide, and matching the spectral resolution and shift of the reference spectra to a particular field instrument. This algorithm is based on a non-linear fitting scheme and is therefore not constrained by many of the assumptions required for the application of linear methods such as classical least squares (CLS). As a result, a more realistic mathematical model of the spectral absorption measurement process can be employed in the curve fitting process. Applications of the algorithm have proven successful in circumventing open path data reduction problems. However, recent studies, by one of the authors, of the temperature and pressure effects on atmospheric absorption indicate there exist temperature and water partial pressure effects that should be incorporated into the NONLIN algorithm for accurate quantification of gas concentrations. This paper investigates the sources of these phenomena. As a result of this study a partial pressure correction has been employed in NONLIN computer code. Two typical field spectra are examined to determine what effect the partial pressure correction has on gas quantification.

Paper Details

Date Published: 10 February 1999
PDF: 10 pages
Proc. SPIE 3534, Environmental Monitoring and Remediation Technologies, (10 February 1999); doi: 10.1117/12.338998
Show Author Affiliations
William Phillips, SpectraSoft Technology (United States)
George M. Russwurm, ManTech Environmental Technology, Inc (United States)

Published in SPIE Proceedings Vol. 3534:
Environmental Monitoring and Remediation Technologies
Tuan Vo-Dinh; Robert L. Spellicy, Editor(s)

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