ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-4491-2011 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, California, USA University of Colorado, CIRES Boulder, Colorado, USA University of New Mexico, Dept. of Earth and Planetary Sciences, Albuquerque, New Mexico, USA 12 05 2011 11 9 4491 4503 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.net/11/4491/2011/acp-11-4491-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/4491/2011/acp-11-4491-2011.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>−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 4.8 % and 6.3 % 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 precision of this bias correction is approximately 1.9 %. The accuracy is driven by the corrections applied to the in situ HDO and H<sub>2</sub>O measurements using flask data taken during the inter-comparison campaign and is estimated to be less than 1 %. Future comparisons of TES data to accurate vertical profiles of in situ measurements are needed to refine this bias estimate.

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