|Bjorneberg, David - Dave|
Submitted to: Vibrational Spectroscopy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/26/2006
Publication Date: 8/17/2006
Citation: Shao, L., Pollard, M.J., Griffiths, P.R., Westermann, D.T., Bjorneberg, D.L. 2006. Rejection criteria for open-path Fourier transform infrared spectrometry during continuous atmospheric monitoring. Vibrational Spectroscopy. 43:78-85. Interpretive Summary: Open-path Fourier transform infrared (OP/FT-IR) spectrometry is a sensitive and non-invasive method for measuring atmospheric compounds. When weather or environmental conditions are not optimal, as much as 10% of the readings may be invalid due to interference. An automatic exclusion procedure was developed to identify readings that should be rejected. This procedure reduces the time required to quality check data and allows measurements to be made at 1-min intervals over a period of several days.
Technical Abstract: Over 32,000 interferograms measured during open-path Fourier transform infrared (OP/FT-IR) measurements at dairy and hog farms were evaluated for anomalies. Five types of anomalies could be distinguished: a reduction in the interferogram intensity because of weather-related optical misalignment; an increase in the amplitude of interferograms measured with too short a path-length that leads to a non-linear detector response; a periodic interference caused by wind-induced vibrations; the presence of spikes in the interferogram; and an increase in the noise level of the interferogram (and hence of the spectrum) because of the effect of electrical interference. Prior to testing for the presence of anomalous data, each interferogram is subjected to a high-pass filter. A noise level index is then calculated from the wings of the interferogram and interferograms are rejected if the value of this parameter is too high. When the criteria developed in this project are applied, OP/FT-IR spectra may be measured at 1-min intervals over a period of several days.