Remote Sensing of the Vertical Ozone Profile Using A Tunable CO2 Sideband Laser Heterdyne Spectrometer

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A continuously tunable and very compact mid-infrared (9-12 um) CO2 sideband laser spectrometer was developed under prior a NSF grant (ATM-9011067). This instrument has been used to obtain accurate data on absorption line positions, line strengths, line width and frequency shift of NH3 molecules. The application of this laser for remote sensing of stratospheric ozone (O3) and HNO3 will be investigated in this project. Development of the technique will also be extended to other stratospheric molecules such as CF2Cl2 (Frcon-12). This two year year research program will obtain quantitative vertical concentration profiles of these species by conducting the field measurements using a heterodyne radiometer with the tunable sideband CO2 laser as a local oscillator. The field measurements will be analyzed by using existing models and comparing them with existing vertical profiles. A parallel study will be performed to measure the critical line shape parameters for O2 under controlled laboratory conditions. In this effort, the tunable sideband laser spectrometer will provide direct absorption measurements under simulated stratospheric conditions with sufficient resolution to obtain the desired spectroscopic line parameters. In the first year, a heterodyne radiometer system consisting of a solar- tracker, optical combiner, a local oscillator, a photomixer, RF filter band and signal processor will be designed, assembled and calibrated. In particular, noise characteristics of the sideband laser will be studied by heterodyining with blackbody radiation and potential methods to reduce the amplitude and phase noise will be explored. The goal is to approach short-noise- limited performance and thereby achieve maximum signal to noise ratio for the heterodyne system. In parallel, a system for delivering and analyzing gas mixtures will be constructed and calibrated. During the second year, laboratory absorption measurements of O2, HNO3 and CF2Cl2 will be perfo rmed with extremely high resolution (+0.00001 cm-) under stratospheric conditions to obtain accurate correlations between line shape parameters and analyte concentrations. Field measurements will be conducted and analyzed simultaneously utilizing the newly acquired line shape parameters. A model which yields an accurate vertical ozone concentration profile between 15 to 50 km will be developed. The ultimate application for the model lies in the interpretation of the dynamics and chemistry related to the stratospheric ozone layer.