Abstract
Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) onboard the MetOp satellite measures carbon monoxide (CO) on a global scale, twice a day. CO total columns and vertical profiles are retrieved in near real time from the nadir radiance spectra measured by the instrument in the thermal infrared (TIR) spectral range. This paper describes the measurement vertical sensitivity and provides a first assessment of the capabilities of IASI to measure CO distributions. On the global scale, 0.8 to 2.4 independent pieces of information are available for the retrieval. At mid latitudes, the information ranges between 1.5 and 2, which enables the lower and upper troposphere to be distinguished, especially when thermal contrast is significant. Global distributions of column CO are evaluated with correlative observations available from other nadir looking TIR missions currently in operation: the Measurements of Pollution in the Troposphere (MOPITT) onboard TERRA, the Atmospheric Infrared Sounder (AIRS) onboard AQUA and the Tropospheric Emission Spectrometer (TES) onboard AURA. The IASI CO columns are compared with MOPITT, AIRS and TES CO columns, adjusted with the a priori, for three different months: August 2008, November 2008 and February 2009. On average, total column discrepancies of about 7% are found between IASI and the three other sounders in the Northern Hemisphere and in the equatorial region. However when strong CO concentrations are present, such as during fire events, these discrepancies can climb as high as 17%. Instrument specifications of IASI versus other missions are also discussed.
Highlights
As one of the most important precursors of ozone (O3), carbon monoxide (CO) is an important trace gas for the understanding of both air quality and climate forcing
We focus on comparison of monthly averaged total column CO distributions for three months at different seasons, in order to derive general trends in terms of discrepancies
This paper presents a first assessment of the capabilities of Infrared Atmospheric Sounding Interferometer (IASI) to measure CO on the global scale
Summary
As one of the most important precursors of ozone (O3), carbon monoxide (CO) is an important trace gas for the understanding of both air quality and climate forcing. Nadir viewing remote sensors offer the advantage of sounding into the lower atmosphere, with a limited vertical resolution, as was demonstrated from MOPITT/TERRA (Deeter et al, 2003; Edwards et al, 2004), SCIAMACHY (Buchwitz et al, 2004, 2007; de Laat et al, 2006, 2007; Frankenberg et al, 2005), TES/AURA (Rinsland et al, 2006; Luo et al, 2007a and b), AIRS/AQUA (McMillan et al, 2005), and IASI/MetOp (Turquety et al, 2004; Clerbaux et al, 2009) Both nadir viewing and limb viewing instruments are often impacted by the presence of clouds. We conclude with an analysis of the observed agreement and discrepancy
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