Remote sensing by open-path FTIR spectroscopy. Comparison of different analysis techniques applied to ozone and carbon monoxide detection

The analysis of FTIR spectra is usually carried out by commercial programs that use methods based on classical least-squares (CLS) procedures These procedures are normally appropriate to analyse O-P FTIR spectra, but some occasional discrepancies with standard extractive methods have been observed.In this work, a line-by-line method (SFIT) is additionally used. Our purpose is to explain the sporadic discrepancies observed between CLS and standard extractive method results and to study the capability of both methods (CLS and SFIT) to analyse open-path measurements. This capability has been studied for ozone and carbon monoxide.It has been demonstrated that in CLS-based methods discrepancies are induced by the experimental background reference spectrum. In these cases, SFIT results are in very good agreement with the standard extractive methods.