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[1] We present global, vertical profile estimates of the HDO/H 2 O ratio from the Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS) Aura satellite. We emphasize in this paper the estimation approach and error characterization, which are critical to determining the very small absolute concentration of HDO relative to H 2 O and its uncertainty. These estimates were made from TES nadir-viewing (downlooking) thermal infrared spectral radiances observed on 20 September 2004. Profiles of HDO and H 2 O are simultaneously estimated from the observed radiances and a profile of the ratio is then calculated. This simultaneous, or ''joint,'' estimate is regularized with an a priori covariance matrix that includes expected correlations between HDO and H 2 O. This approach minimizes errors in the profile of the HDO/H 2 O ratio that are due to overlapping HDO and H 2 O spectroscopic lines. Under clear-sky conditions in the tropics, TES estimates of the HDO/H 2 O ratio are sensitive to the distribution of the actual ratio between the surface and about 300 hPa with peak sensitivity at 700 hPa. The sensitivity decreases with latitude through its dependence on temperature and water amount. We estimate a precision of approximately 1% to 2% for the ratio of the HDO/H 2 O tropospheric densities; however, there is possibly a bias of approximately 5% in the ratio due to the HDO spectroscopic line strengths. These global observations clearly show increased isotopic depletion of water vapor at higher latitudes as well as increased depletion in the upper troposphere versus the lower troposphere.

Abstract-Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). With the exception of HIRDLS, all of the instruments are performing as expected, and HIRDLS will likely be able to deliver most of their planned data products. We summarize the mission, instruments, and synergies in this paper.

The Tropospheric Emission Spectrometer (TES) is an imaging infrared Fourier-transform spectrometer scheduled to be launched into polar Sun-synchronous orbit aboard the Earth Observing System's Aura satellite in June 2003. The primary objective of the TES is to make global three-dimensional measurements of tropospheric ozone and of the physical-chemical factors that control its formation, destruction, and distribution. Such an ambitious goal requires a highly sophisticated cryogenic instrument operating over a wide frequency range, which, in turn, demands state-of-the-art infrared detector arrays. In addition, the measurements require an instrument that can operate in both nadir and limb-sounding modes with a precision pointing system. The way in which these mission objectives flow down to the specific science and measurement requirements and in turn are implemented in the flight hardware are described. A brief overview of the data analysis approach is provided.

The Tropospheric Emission Spectrometer (TES) on the Earth Observing System (EOS)‐Aura spacecraft measures global profiles of atmospheric ozone with vertical resolution of 6–7 km in the troposphere for the nadir view. For a first validation of TES ozone measurements we have compared TES‐retrieved ozone profiles to ozonesondes from fall, 2004. In some cases the ozonesonde data are from dedicated launches timed to match the Aura overpass, while other comparisons are performed with routine data available from the Southern Hemisphere Additional Ozonesonde (SHADOZ) archive and World Ozone and Ultraviolet Data Center (WOUDC) data archives. We account for TES measurement sensitivity and vertical resolution by applying the TES‐averaging kernel and constraint to the ozonesonde data before differencing the profiles. Overall, for V001 data, TES ozone profiles are systematically higher than sondes in the upper troposphere but compare well in the lower troposphere, with respect to estimated errors. These comparisons show that TES is able to detect relative variations in the coarse vertical structure of tropospheric ozone.