ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-25355-2010 Estimate of bias in Aura TES HDO/H<sub>2</sub>O profiles from comparison of TES and in situ HDO/H<sub>2</sub>O measurements at the Mauna Loa Observatory Worden J. 1 Noone D. 2 Galewsky J. 3 Bailey A. 2 Bowman K. 1 Brown D. 2 Hurley J. 3 Kulawik S. 1 Lee J. 1 Strong M. 3 Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA University of Colorado, Boulder, CO, USA University of New Mexico, Albuquerque, NM, USA 01 11 2010 10 11 25355 25388 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/10/25355/2010/acpd-10-25355-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/25355/2010/acpd-10-25355-2010.pdf

The Aura satellite Tropospheric Emission Spectrometer (TES) instrument is capable of measuring the HDO/H<sub>2</sub>O ratio in the lower troposphere using thermal infrared radiances between 1200 and 1350 cm<sup>&minus;1</sup>. However, direct validation of these measurements is challenging due to a lack of in situ measured vertical profiles of the HDO/H<sub>2</sub>O ratio that are spatially and temporally co-located with the TES observations. From 11 October through 5 November 2008, we undertook a campaign to measure HDO and H<sub>2</sub>O at the Mauna Loa observatory in Hawaii for comparison with TES observations. The Mauna Loa observatory is situated at 3.1 km above sea level or approximately 680 hPa, which is approximately the altitude where the TES HDO/H<sub>2</sub>O observations show the most sensitivity. Another advantage of comparing in situ data from this site to estimates derived from thermal IR radiances is that the volcanic rock is heated by sunlight during the day, thus providing significant thermal contrast between the surface and atmosphere; this thermal contrast increases the sensitivity to near surface estimates of tropospheric trace gases. The objective of this inter-comparison is to better characterize a bias in the TES HDO data, which had been previously estimated to be approximately 5% too high for a column integrated value between 850 hPa and 500 hPa. We estimate that the TES HDO profiles should be corrected downwards by approximately 4.1% and 5.6% for Versions 3 and 4 of the data, respectively. These corrections must account for the vertical sensitivity of the TES HDO estimates. We estimate that the uncertainty of this bias correction is approximately 1%. However, future comparisons of TES data to other sensors are needed to refine this bias estimate because these uncertainties are primarily derived from only three sets of measurements.

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