Water Vapor Spectroscopic Data for Lidar Water Vapor Measurements in the 720-nm Wavelength Region

Abstract

The Differential Absorption Lidar (DIAL) technique can be used to remotely measure profiles of atmospheric gases such as water vapor. The application of this technique requires accurate water vapor spectroscopic data on line strength, pressure broadening, pressure shifts, and linewidth temperature dependence in the wavelength region of interest. As part of NASA's atmospheric research program, the NASA Langley Research Center is currently involved in developing a DIAL system for the Lidar Atmospheric Sensing Experiment (LASE)(1). This DIAL system will use tunable Alexandrite lasers and operate from a high-altitude ER-2 (extended range U-2) aircraft for the measurement of tropospheric water vapor distributions. To support this experiment, a high- resolution spectroscopy setup consisting of a cw ring dye laser and two White cells was used to provide measurements of needed water vapor line parameters. Measurements were made of the absorption line strength, width, and pressure shift in air, and the temperature dependence of linewidth and shift for 270 absorption lines lying between 717 and 738 nm. The line shapes were also studied, and deviations from the standard Voigt profile were found resulting from the Dicke-narrowing effect. In addition, linewidths and shifts have been investigated in various buffer gases including nitrogen, oxygen, argon, and xenon.