CO2 lidars have heretofore been used to measure water vapor concentrations primarily using the 10R(20) line at 10.247 μm, which has a strong overlap with a water vapor absorption line. This paper discusses the use of that line as well as other CO2 laser lines for which the absorption coefficients are weaker. The literature on measurement of water vapor absorption coefficients using CO2 lasers is reviewed, and the results from four laboratories are shown to be generally consistent with each other after they are normalized to the same partial pressure, temperature, and ethylene absorption coefficient for the 10P(14) CO2 laser line; however, the agreement with the Air Force Geophysics Laboratory's hitran and fascod 2 spectral data tapes is not good either for the water vapor absorption lines or for the water vapor continuum. Demonstration measurements of atmospheric water vapor have been conducted using the Mobile Atmospheric Pollutant Mapping System, a dual CO2 lidar system using heterodyne detection. Results are discussed for measurements using three sets of laser line pairs covering a wide range of water vapor partial pressures.
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Adjusted to 760 Torr, 300 K.
At 360 Torr, converted to 35.96 atm−1 cm−1 at 760 Torr.
Table II
Water Vapor Absorption Coefficients at 300 K, 10-Torr Partial Pressure, and α C2H4 = 34.76 atm−1 cm−1, for Selected CO2 Laser Lines (10−6 cm−1) for 10 Torr, 300 K
Ammonia interference possible for this CO2 laser line.
Table III
Comparison of Water Vapor Absorption Coefficients Determined Using CO2 Lasers with the Values on the AFGL Spectral Data Tapes for 10-Torr Partial Pressure, 300 K, α C2H4 = 35.0 atm−1 cm−1
Ref. 30.
Includes 6.24% uncertainty due to the uncertainty in determining the value of the ethylene absorption coefficient for the 10P(14) CO2 laser line.
JPL and AFGL29 determinations estimated to be accurate to 10%.
Table IV
CO2-Laser Determined Values for the Water Vapor Continuum Absorption for 300 K, 10-Torr Partial Pressure, 760-Torr Total Pressure
Adjusted to 760 Torr, 300 K.
At 360 Torr, converted to 35.96 atm−1 cm−1 at 760 Torr.
Table II
Water Vapor Absorption Coefficients at 300 K, 10-Torr Partial Pressure, and α C2H4 = 34.76 atm−1 cm−1, for Selected CO2 Laser Lines (10−6 cm−1) for 10 Torr, 300 K
Ammonia interference possible for this CO2 laser line.
Table III
Comparison of Water Vapor Absorption Coefficients Determined Using CO2 Lasers with the Values on the AFGL Spectral Data Tapes for 10-Torr Partial Pressure, 300 K, α C2H4 = 35.0 atm−1 cm−1
Ref. 30.
Includes 6.24% uncertainty due to the uncertainty in determining the value of the ethylene absorption coefficient for the 10P(14) CO2 laser line.
JPL and AFGL29 determinations estimated to be accurate to 10%.
Table IV
CO2-Laser Determined Values for the Water Vapor Continuum Absorption for 300 K, 10-Torr Partial Pressure, 760-Torr Total Pressure
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