Observations of Earth's Downwelling Far-Infrared Spectral Radiance at Cerro Toco, Chile, and Table Mountain, California

The Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument has recorded observations of downwelling spectral radiance at two high-altitude, dry locations. The reported spectral range is 200 to 800 wavenumbers (50 to 12.5μm). In late 2009 FIRST observed the downwelling far-infrared spectra at Cerro Toco, Chile, at an altitude of 17,500 feet above sea level. In late 2012, FIRST made similar observations at Table Mountain, California, at 7500 feet. Both sets of ground-based observations were accompanied by radiosonde measurements to provide temperature and moisture profiles that can be used to compute the far-infrared radiance with an existing line-by-line radiative transfer code for comparison with the FIRST observations. In this talk we show comparisons between FIRST observations and calculated radiances. The comparisons are presented with consideration of measurement and computation radiance uncertainties. The uncertainties in FIRST spectra are based on a recent laboratory calibration of the instrument. Implications from the model/data comparisons, for the spectroscopy of water vapor in the 400-600 wavenumber region, will be discussed.