Abstract: The subject matter discloses a method for detecting concentration of air contaminants, comprising obtaining an average sample single beam value, the average sample single beam value comprises a first set of single beam measurements obtained from a detector; obtaining an average background single beam value, the average background single beam value comprises a second set of single beam measurements obtained from the detector; comparing the average sample single beam value to the average background single beam value to determine the concentration of air contamination; continuously updating the averages upon detection of new single beam measurements; wherein the second set of single beam measurements comprises a plurality of single beam measurements that were detected by the detector prior to the detection of the single beam measurements included in the first set of single beam measurements. In some cases, the first set partially overlaps with the second set.

Abstract: An improved method for use with an open-path fast Fourier infrared spectrometer performs real-time, spectral alignment on measured interferograms to reduce measuremental errors. The improved method includes the step of selecting a plurality of water-vapor lines in a defined spectral region and comparing the centerline of these measured water vapor lines to a reference library. From these comparisons, the spectrometer calculates correction factors to apply to the spectrometer bandwidth. The improved spectrometer performs transform functions on selected segments of the spectrometer bandwidth which introduce integer-continuous corrective shifts on subsequently measured interferogram data.

Abstract: An improved open-path fast Fourier infrared spectrometer includes a circuit or algorithm which performs real-time, spectral alignment on measured interferograms to reduce measuremental errors. The improved spectrometer measures selected water vapor lines in a measurement path and compares the centerline of these measured water vapor lines to a reference library. From two or more such comparisons within the spectrometer bandwidth, the spectrometer calculates correction factors for the entire bandwidth. The improved spectrometer performs an overlap and add algorithm which applies the correction factors to perform bandwidth segment-specific shifts on subsequently measured interferograms.