Multiwavelength technique for open-path measurements of the concentrations of atmospheric constituents

A multiwavelength technique for open-path spectrophotometric measurements of the concentrations of the principal constituents of the atmosphere is presented. It uses a standard least squares procedure to minimize deviations of the calculated optical thickness of the working path from the measured value. The novel feature of this technique is that the effects of various sources of error on the computational results are interpreted as the difference in spectra of the probe radiation propagating along the working path and a comparison path. This difference yields a systematic error that is independent of the actual concentrations. The advantage of the multiwavelength technique is that an increased number of measurement wavelengths significantly reduces the effect of the various sources of error on the results.