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The inter-comparison of IASI water vapour retrieval schemes

The inter-comparison of IASI water vapour retrieval schemes. Martin Stengel , Marc Schröder, Nadine Schneider, Theo Steenbergen, Marc Schwärz, Katie Lean, Roger Saunders, Adrian Doicu. Outline. Background IASI assessment in GlobVapour Retrieval systems Comparison approach First results

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The inter-comparison of IASI water vapour retrieval schemes

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  1. The inter-comparison of IASI water vapourretrieval schemes Martin Stengel, Marc Schröder, Nadine Schneider, Theo Steenbergen,Marc Schwärz, Katie Lean, Roger Saunders, Adrian Doicu

  2. Outline • Background • IASI assessment in GlobVapour • Retrieval systems • Comparison approach • First results • Outlook

  3. Outline • Background • IASI assessment in GlobVapour • Retrieval systems • Comparison approach • First results • Outlook

  4. Background • Previous studies and investigations have shown the benefit of Infrared Atmospheric Sounding Interferometer (IASI) measurements for atmospheric analysis in one- and multi-dimensional analysis schemes. • Beside IASI’s application in e.g. NWP frameworks, growing long-term records of its measurements suggest the utilization of IASI retrieval products of atmospheric parameters for climate monitoring and subsequently for e.g. evaluation of climate models (i.e. hintcast simulations) • The (inter-) comparisons of IASI retrieval schemes has only been tackled by a few studies so far (e.g. Hilton et al., 2009)

  5. Background • As a substantial part of the ESA DUE GlobVapour project, DWD and project partners are conducting a comprehensive IASI retrieval inter-comparison study. • The focus of this assessment is directed towards the identification of an optimal algorithm scheme for climate monitoring of atmospheric water vapour. • Comparison criteria include the retrieval quality and application limitations, but also the performance and applicability in re-processing frameworks. • The study will include several IASI retrieval algorithms provided by the project partners (DLR, UK Met-Office, DWD) and additionally participating groups (EUMETSAT, NOAA).

  6. Background • Hilton et al. (2009): An investigation into the performance of retrievals of temperature and humidity from IASI: • Nine different physically based retrieval schemes were applied to 25 clear sky cases IASI footprints over the Gulf of Mexico, which were characterized by near-coincident dropsonde observations taken during the Joint Airborne IASI Validation Experiment (JAIVEx) campaign of April-May 2007 • On focus of this study: Can fine vertical structure and sharp gradients be seen in the retrievals even though if they are not present in the a priori profile information used by the retrieval system.

  7. Background • Case study of dry layer atapprox. 720 hPa: (from Hilton et al., 2009)

  8. Background • Case study of dry layer atapprox. 720 hPa: (from Hilton et al., 2009)

  9. Background • Assessing the impact of type of background information (from Hilton et al., 2009)

  10. Background • Assessing the impact of type of background information (from Hilton et al., 2009)

  11. Outline • Background • IASI assessment in GlobVapour • Retrieval systems • Comparison approach • First results • Outlook

  12. IASI assessment in GlobVapour • The focus of this assessment is directed towards the identification of an optimal algorithm scheme for monitoring of atmospheric water vapour. • It was planned to include the ‘winner’-algorithm in a joint-retrieval processor (together with SEVIRI LCWV) to produce a superior water vapour dataset for three tropospheric layers, benefiting from the high quality, vertically-resolved IASI retrievals and the high temporal resolution of SEVIRI retrievals (Nowcasting SAF retrieval system) • Goals: • Determination of absolute accuracy of each participating retrieval by comparison with ground-based reference measurements • Analysis of the deviations among the retrieval systems and their strengths and weaknesses with respect to a long-term analysis of the water vapour in a reprocessing framework

  13. IASI assessment in GlobVapour • Participating groups • DWD (1D-Var) • UK Met Office (1D-Var) • DLR - German Aerospace Center • NOAA • EUMETSAT (v4, v5) • Data production • The IASI retrieval algorithms will be run at each of the participating institutions. • Provision of retrieved profiles of temperature and specific humidity to DWD (including additional information, e.g. vertical grid, latitude, longitude, quality flags and time stamps, …) • All this information will be inferred for 121 footprints in a 11-by-11 footprints box, which is centered at the corresponding reference sites.

  14. IASI assessment in GlobVapour • Reference sites & data (3 ARM, 2 GUAN sites) • Lindenberg, Sodankyla, Barrow, Lamont, Nauru • Six months considered (July, August 2007, and January, June, August, December 2008) • TCWV (ground-based MWR), WV profiles (radiosondes)

  15. IASI assessment in GlobVapour • Data availability

  16. IASI assessment in GlobVapour • Data availability 1 3 2

  17. IASI assessment in GlobVapour • Selection criteria: • Select closest clear-sky-retrieval pixel (with respect to the reference site) from each retrieval • Select case if MWR ‘says’ clear-sky (LWP .lt. threshold) • All selected pixels from all retrievals have to match site’s location within 0.75° distance and temporally match the ground radiosonde measurement within ± 3 hours

  18. IASI assessment in GlobVapour • Case 1: June 2008, Lindenberg • UKMO 1D-Var only partly available

  19. IASI assessment in GlobVapour • Case 1: June 2008, Lindenberg • UKMO 1D-Var only partly available ERA-Interim forecast might bevery closed to radiosondes sincethey are assimilated

  20. IASI assessment in GlobVapour • Case 2: August 2008, Lamont

  21. IASI assessment in GlobVapour • Case 2: August 2008, Lamont

  22. IASI assessment in GlobVapour • Case 3: July 2007, Lamont

  23. IASI assessment in GlobVapour • Case 3: July 2007, Lamont Missing bias correction?!

  24. Summary and Outlook • IASI retrieval assessment has started within the ESA DUE GlobVapour project • First results have been collected and inter-compared • More data needed to draw possible conclusions • NOAA retrieval data will included soon, maybe also EUMETSAT v5

  25. Summary and Outlook • Also use other pixels in comparisons… • Advanced validation tools to be used: • Software following the approach of Pougatchev (2008), Pougatchev et al. (2009). • The model developed accounts for differences in horizontal, vertical, and temporal resolution as well as noise level of the IASI instrument and radiosondes. • We plan to adapt this metho-dology also to the problem ofcomparison of TCWV estimatesto ground-based observationsand to comparisons among theproducts.

  26. Fiona Hilton, Paolo Antonelli, Xavier Calbet, Tim Hultberg, Lydie Lavanant, Xu Liu, Guido Masiello, Stuart Newman, Jonathan Taylor, Carmine Serio, Daniel Zhou, 2009: AN INVESTIGATION INTO THE PERFORMANCE OF RETRIEVALS OF TEMPERATURE AND HUMIDITY FROM IASI, Conference proceeding EUMETSAT conference 2009 • N. Pougatchev, T. August, X. Calbet, T. Hultberg, O. Oduleye, P. Schlüssel2, B. Stiller, K. St. Germain, and G. Bingham, 2009: IASI temperature and water vapor retrievals – error assessment and validation, Atmos. Chem. Phys., 9, 6453–6458 • Pougatchev, N. S.: Validation of atmospheric sounders by correlative measurements, Appl. Opt., 47,4739–4748, 2008. www.globvapour.info Thank you

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