IASI on Metop-A: Operational Level 2 retrievals after five years in orbit Thomas August n , Dieter Klaes, Peter Schl ¨ ussel, Tim Hultberg, Marc Crapeau, Arlindo Arriaga, Anne O’Carroll, Dorothe ´ e Coppens, Rose Munro, Xavier Calbet EUMETSAT, Eumetsat Allee 1, D-64295 Darmstadt, Germany article info Available online 9 March 2012 Keywords: Hyperspectral infrared sounding IASI Metop Operational retrievals abstract Geophysical parameters from the IASI instrument on Metop-A are essential products provided from EUMETSAT’s Central Facility in near real time. They include vertical profiles of temperature and humidity, related cloud information, surface emissivity and temperature, and atmospheric composition parameters (CO, ozone and several other trace gases). As compared to previous operational processor versions, the latest processor version 5 delivers significant improvements in retrieval performance for most major products. These include improvements to cloud properties products, cloud detection (with a positive impact on the knowledge of the sea surface temperature, SST), the temperature profile (especially in the mid and upper troposphere), and ozone and carbon monoxide total columns. This paper provides a comprehensive summary of the processing algorithms, the latest scientific developments, and the related validation studies and activities. It concludes with a discussion of the future outlook. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. The EUMETSAT Polar System The EUMETSAT Polar System (EPS) is EUMETSAT’s contribution to the Initial Joint Polar System (IJPS). The IJPS provides observations for operational meteorology and climate monitoring from both the mid morning orbit, under the responsibility of EUMETSAT, and the afternoon orbit, under the responsibility of NOAA. The Metop satellite series is the space component of the EUMETSAT Polar System (EPS). Metop-A, the first in a series of three spacecraft, was launched in October 2006. Since May 2007 it has provided data continuously from the eight meteorological instruments on board. The three Metop satellites (with launches of Metop-B and -C planned in 2012 and 2017, respectively) will provide a continuous service from the mid-morning orbit (9:30 Local Solar Time equator crossing time, descending node) for at least 15 years. More details on the EPS/Metop system can be found in [1]. The most innovative and one of the key instruments on Metop is the Infrared Atmospheric Sounding Interferom- eter (IASI). Three instruments were developed for Metop by CNES (Centre National d’Etudes Spatiales) in coopera- tion with EUMETSAT. They are built to provide tempera- ture, moisture with unprecedented accuracy and resolution and additionally to provide information for the monitoring of atmospheric trace gases. IASI is a Michelson interferometer measuring in the infrared. It measures 8461 spectral samples between 3.62 and 15.5 mm with a resolu- tion of 0.5 cm 1 after apodisation. IASI scans across-track in 30 successive elementary fields of view (EFOV), each composed of 4 instantaneous fields of view (IFOV). The EFOVs span a 748.331 range, symmetric with respect to Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jqsrt Journal of Quantitative Spectroscopy & Radiative Transfer 0022-4073/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jqsrt.2012.02.028 n Corresponding author. Tel.: þ49 6151 807 5650; fax: þ49 6151 807 8380. E-mail address: thomas.august@eumetsat.int (T. August). Journal of Quantitative Spectroscopy & Radiative Transfer 113 (2012) 1340–1371