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Laboratory Spectroscopy of CO2 for Earth Observations


EMSL Project ID
25719

Abstract

For several instruments on the AURA and AQUA satellites, retrievals of atmospheric temperature profiles are based on observed radiances in infrared spectral regions where emission from atmospheric CO2 predominates. Microwindows in the strong fundamental CO2 band system at 15 μm are used for some of these retrievals. While the accuracies of the radiances observed at the satellite are ~0.2 K, the residuals between the data and forward model calculations in these CO2 spectral regions are still large with the maximum brightness temperature differences approaching ~2 K in some regions. In order to achieve improved retrieval accuracy, systematic errors in the forward model must be reduced, especially those associated with errors in the spectral line calculation. Since retrievals of the concentration profiles of other atmospheric gases (e.g., ozone) depend on accurate knowledge of the temperature profiles, it is critical to understand the source of these apparently systematic errors in the CO2 spectroscopic parameters.
We propose laboratory measurements of the 15-μm band system of CO2 to accurately determine line intensities, air- and N2-broadened widths and pressure-induced line shifts, along with their temperature dependences. Line mixing and other non-Lorentz, non-Voigt line shapes will also be assessed. Spectra will be recorded with high-resolution Fourier transform spectrometers and temperature-controlled sample cells. Analysis will be done using a multispectrum fitting technique to retrieve the spectroscopic parameters. Results will be communicated to members of the TES and AIRS Science Teams for testing in their forward model calculations. The final results will also be contributed to future updates of the HITRAN spectroscopic parameters database.

Project Details

Project type
Exploratory Research
Start Date
2007-05-01
End Date
2008-05-04
Status
Closed

Team

Principal Investigator

Mary Smith
Institution
NASA Langley Research Center

Team Members

Thomas Blake
Institution
Pacific Northwest National Laboratory

Related Publications

Smith MAH, CP Rinsland, TA Blake, RL Sams, DC Benner, and VM Devi. 2008. "Low Temperature Measurements of HCN Broadened by N2 in the 14-micron Spectral Region." Journal of Quantitative Spectroscopy and Radiative Transfer 109(6):922-951. doi:10.1016/j.jqsrt.2007.12.017