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A method for passive measurements of water vapor concentration in the atmosphere in the presence of solar radiation has been proposed and tested. The location of the measurements is the northeast of the Moscow region. When processing the results of measurements carried out on a single water absorption line, a coincidence of experimental data and data obtained from direct meteorological measurements with an error of no more than ~7.5 % was revealed. It was also found that on the water absorption line in the region of 1653 nm, the interfering factor is the nearby methane absorption line, which introduces a systematic error in the measurement results, and the results turn out to be underestimated. A possible reason is that the absorption cross section of methane molecules is ~4 orders of magnitude larger than that of water vapor molecules and light radiation is absorbed to a greater extent by methane, reducing the fraction of absorption of water vapor at a wavelength close to the methane absorption line. Compensatory corrections have been introduced to determine the concentration and moisture content in the atmospheric column with an accuracy of several percent at this wavelength. The proposed technique allows both long-term monitoring of concentration and moisture content in the atmosphere and obtaining operational information in real time. The results of the measurements performed are, on average, consistent with the results of measurements obtained using radiometers operating in the ultrahigh frequency range.
Vladimir I. Grigorievsky (Mon,) studied this question.