the inter-comparison of iasi water vapour retrieval schemes

The inter-comparison of IASI water vapourretrieval 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

• Outlook

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)

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).

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.

Background

• Case study of dry layer atapprox. 720 hPa:

(from Hilton et al., 2009)

Background

• Assessing the impact of type of background information

(from Hilton et al., 2009)

Outline

• Background

• IASI assessment in GlobVapour• Retrieval systems• Comparison approach• First results

• Outlook

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


• 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.


• 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)


• Data availability

Jul 2007 Aug 2007 Jan 2008 Jun 2008 Aug 2008 Dec 2008

Site Li S B L N Li S B L N Li S B L N Li S B L N Li S B L N Li S B L N

UKMO y y y y y y y y y y - - - - - y y y y y - - - - - y y y y y

NOAA - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

EUMETSAT v4 - - - - - - - - - - y y y y y y y y y y y y y y y y y y y y

EUMETSAT v5 - - - - - - - - - - - - - - - - - - - - y y y y y - - - - -

DLR y - - - - y - - - - - - - - - - - - - - - - - - - - - - - -

DWD y y y y y y y y y y y y y y y y y y y y y y y y y y y y y y


• Data availability




NOAA - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


EUMETSAT v5 - - - - - - - - - - - - - - - - - - - - y y y y y - - - - -

DLR y - - - - y - - - - - - - - - - - - - - - - - - - - - - - -


1 23


• 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


• Case 1: June 2008, Lindenberg• UKMO 1D-Var only partly available


• Case 1: June 2008, Lindenberg• UKMO 1D-Var only partly available

ERA-Interim forecast might bevery closed to radiosondes sincethey are assimilated


• Case 2: August 2008, Lamont


• Case 3: July 2007, Lamont


• Case 3: July 2007, Lamont

Missing bias correction?!

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




NOAA - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


EUMETSAT v5 - - - - - - - - - - - - - - - - - - - - y y y y y - - - - -

DLR y - - - - y - - - - - - - - - - - - - - - - - - - - - - - -


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.

• 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.

Thank you

www.globvapour.info

the inter-comparison of iasi water vapour retrieval schemes

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