Minimizing the effect of extraneous spikes in open-path Fourier transform infrared interferograms

Intense spikes caused by extraneous factors are sometimes found in the interferograms of open-path Fourier transform infrared (OP/FT-IR) measurements. Those spikes result in dominant oscillations in the corresponding spectra and make the true spectral features indistinguishable from the noise. Three techniques were designed to remove the spikes: replacing the affected region by zeroes; grafting the data from the corresponding region on the other side of the centerburst ("homografting"); and grafting the data from the same region on the same side of the centerburst from a neighboring interferogram ("heterografting"). Results showed that all three techniques were effective to remove the spikes, but at the cost of introducing more noise into the corresponding spectrum. The performance of the heterograft technique was the best in terms of noise reduction. The factors affecting the noise level of spectra computed from spike-removed interferograms were also explored. A procedure was proposed to minimize the effect of spikes on OP/FT-IR spectra, and a Matlab program with a graphical user interface is available upon request to facilitate the implementation.