Atmospheric Measurement Techniques Discussions www.atmos-meas-tech-discuss.net 1867-8610 3 4 2010 10.5194/amtd-3-3489-2010 http://www.atmos-meas-tech-discuss.net/3/3489/2010/ http://www.atmos-meas-tech-discuss.net/3/3489/2010/amtd-3-3489-2010.html http://www.atmos-meas-tech-discuss.net/3/3489/2010/amtd-3-3489-2010.pdf 3489 3534 2010-08-18 A geostationary thermal infrared sensor to monitor the lowermost troposphere: O₃ and CO retrieval studies M. Claeyman marine.claeyman@aero.obs-mip.fr J.-L. Attié V.-H. Peuch L. El Amraoui W. A. Lahoz B. Josse P. Ricaud T. von Clarmann M. Höpfner J. Orphal J.-M. Flaud D. P. Edwards K. Chance X. Liu F. Pasternak R. Cantié Laboratoire d'Aérologie, Université de Toulouse, CNRS/INSU, Toulouse, France CNRM-GAME, Météo-France and CNRS URA 1357, Toulouse, France NILU, N-2027 Kjeller, Norway Karlsruhe Institute of Technology, IMK, Karlsruhe, Germany Laboratoire Interuniversitaire des Systèmes Atmosphériques, CNRS UMR 7583, Université de Paris-Est, Créteil, France National Center for Atmospheric Research, Boulder, Colorado, USA Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA Astrium-EADS, Toulouse, France This paper describes the capabilities of a nadir thermal infrared (TIR) sensor proposed for embarkation onboard a geostationary platform to monitor ozone (O₃) and carbon monoxide (CO) for air quality (AQ) purposes. To assess the capabilities of this sensor we perform idealized retrieval studies considering typical atmospheric profiles of O₃ and CO over Europe with different instrument configurations (signal to noise ratio and spectral sampling interval) using the KOPRA forward model and the KOPRA-fit retrieval scheme based on the Tikhonov-Phillips regularization. We then select a configuration, referred to as GEO-TIR, optimized for providing information in the lowermost troposphere (LmT; 0–3 km in height). For the GEO-TIR configuration we obtain around 1.5 degrees of freedom for O₃ and 2 for CO at altitudes between 0 and 15 km. The error budget of GEO-TIR, calculated taking account of the principal contributions to the error (namely, temperature, measurement error, smoothing error) shows that information in the LmT can be achieved by GEO-TIR. We also retrieve analogous profiles from another geostationary infrared instrument with characteristics similar to the Meteosat Third Generation Infrared Sounder (MTG-IRS) which is dedicated to numerical weather prediction, referred to as GEO-TIR2. Comparison between GEO-TIR and GEO-TIR2 allows us to quantify the added value of GEO-TIR, a mission complementing the AQ observing system. To better characterize the information provided by GEO-TIR and GEO-TIR2 in the LmT, we retrieve two typical profiles of O₃ and CO for different thermal contrast ranging from –10 K to 10 K. The shape of the first averaging kernel (corresponding to the surface level) confirms that GEO-TIR has good sensitivity to CO in the LmT and also to O₃ for high positive thermal contrast. GEO-TIR2 has very low sensitivity in the LmT to O₃ but can have sensitivity to CO with high positive thermal contrast. To quantify these results for a realistic atmosphere, we simulate it using the chemical transport model MOCAGE (MOdèle de Chimie Atmospherique à Grande Echelle) – this is the nature run. We simulate the O₃ and CO spatial and temporal distributions from GEO-TIR observations in the LmT in July 2009 over Europe by sampling the nature run. Results show that GEO-TIR is able to capture well the spatial and temporal variability in the LmT for both O₃ and CO, particularly during periods with high positive thermal contrast near the ground and high surface temperature, which results in active photochemistry and a raised planetary boundary layer. These results also provide evidence of the significant added value in the LmT of GEO-TIR compared to GEO-TIR2 by showing GEO-TIR is closer to the nature run than GEO-TIR2 for various statistical parameters (correlation, bias, standard deviation). 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