Cathy Clerbaux

Retrieval of CO from nadir remote-sensing measurements in the infrared by use of four different inversion algorithms

Four inversion schemes based on various retrieval approaches (digital gas correlation, nonlinear least squares, global fit adjustment, and neural networks) developed to retrieve CO from nadir radiances measured by such downward-looking satelliteborne instruments as the Measurement of Pollution in the Troposphere (MOPITT), the Tropospheric Emission Spectrometer (TES), and the Infrared Atmospheric Sounding Interferometer (IASI) instruments were compared both for simulated cases and for atmospheric spectra recorded by the Interferometric Monitor for Greenhouse Gases (IMG). The sensitivity of the retrieved CO total column amount to properties that may affect the inversion accuracy (noise, ancillary temperature profile, and water-vapor content) was investigated. The CO column amounts for the simulated radiance spectra agreed within 4%, whereas larger discrepancies were obtained when atmospheric spectra recorded by the IMG instrument were analyzed. The assumed vertical temperature profile is shown to be a critical parameter for accurate CO retrieval. The instruments line shape was also identified as a possible cause of disagreement among the result provided by the groups of scientist who are participating in this study.

Retrieval of ozone from infrared IASI measurements

The Infrared Atmospheric Sounding Interferometer (IASI), which is due for launch in 2005 aboard the European METOP satellite, will record the infrared radiation of the Earth/atmosphere system in a nadir-viewing geometry. The sensitivity studies carried out on simulated IASI spectra allowed us to highlight its capability to retrieve both total and tropospheric column amounts of ozone. Two algorithms based on neural network techniques have been developed to retrieve these quantities. The averaging kernels characterizing the results show that the information corresponding to the different atmospheric layers can be isolated. However, for the tropospheric ozone retrieval, the lower stratosphere is not totally decoupled, which induces larger uncertainties for the tropospheric columns than for the total columns. Nevertheless, very satisfactory performance has been achieved for both algorithms, with inversion errors smaller than 5 % for the total column retrieval and smaller than 20 % for the tropospheric column retrieval. The Interferometer Monitor for Greenhouse Gases (IMG), which flew aboard the Japanese ADEOS platform was based on the same observation technique as IASI, which enabled us to test our algorithms on real data. Both algorithms have been applied to these data for June 1997. The distributions obtained are in good agreement with the Total Ozone Mapping Spectrometer (TOMS) measurements.

Iasi-NG : un concentré d'innovations technologiques pour l'étude de l'atmosphère terrestre

Les sondeurs infrarouges hyperspectraux embarqués à bord de satellites permettent le suivi, de jour comme de nuit, sur terre comme sur mer, d’un grand nombre de variables climatiques, thermodynamiques et de composants chimiques de l’atmosphère. La mission Iasi, réalisée par le Cnes en collaboration avec Eumetsat dans le cadre de son programme EPS-Metop de satellites météorologiques européens en orbite polaire, a mis en évidence la gamme très vaste des composés chimiques et climatiques qu’il était possible de mesurer ou de détecter grâce aux observations dans l’infrarouge thermique (H2O, CO2, CO, CH4, O3, SO2, NH3, aérosols, etc.) (Phulpin et al., 2011 ; Hilton et al., 2012). Iasi a permis de dresser des cartes d’espèces qui n’avaient jamais pu être observées auparavant à l’échelle globale et depuis l’espace, et assure un suivi en temps quasi réel de gaz clefs pour l’étude du climat et de la chimie atmosphérique. La nécessité pour la météorologie opérationnelle de disposer de sondeurs infrarouges performants a également été illustrée par Iasi : son impact sur les performances des prévisions numériques du temps de différents centres (MétéoFrance, Centre européen pour les prévisions météorologiques à moyen terme, Met Office, etc.) est le plus important parmi les instruments spatiaux aujourd’hui disponibles pris individuellement.

Mesure du SO2 et des cendres volcaniques avec IASI

Les mois de mai et juin 2011 ont ete marques par une succession de trois eruptions volcaniques, mettant en alerte continue les centres responsables de la surveillance des espaces aeriens. Le sondeur infrarouge IASI, embarque sur le satellite MetOp depuis fin 2006, permet de suivre les panaches de SO2 et de cendres associes aux eruptions volcaniques. Cet article illustre les performances de linstrument pour fournir des informations en temps quasi reel pour laviation civile et detaille les methodes qui ont ete mises en oeuvre pour calculer les concentrations en gaz et en particules.

Apport de l'observation satellitaire à l'analyse et à la prévision de la qualité de l'air

This paper presents what can be achieved with the use of satellite observations in the framework of atmospheric composition studies, including for air quality analysis and forecast. The different measurements currently available are presented with their main strengths and limitations. On the basis of examples from recent studies, the use and the gain obtained by these observations are discussed.This includes analysis of pollutant transport events, refinement of the databases used in the models, modeling of satellite observations and data assimilation. The recent Copernicus service is detailed in this context and the prospects for using these observations are finally explained.

La contribution du spatial en France aux sciences de l'atmosphère et du climat

Over the last 30 years, satellite data have been playing a key role for the monitoring of the Earths atmosphere and climate, with an important French and European contribution. This article summarizes the successive stages of a space mission for Earths observation, describes the geophysical variables that can be derived from the measurements, and presents the societal benefits associated with these observations.

Trace gas concentration retrieval from measurements provided by a nadir-looking Fourier transform spectrometer

To prepare the mission of the Infrared Atmospheric Sounding Interferometer (IASI), which will be launched in 2005 aboard the European METOP satellite, the measurement capability to retrieve trace gases concentrations from nadir radiances was investigated. This included sensitivity studies, development of an innovating inversion algorithm, cloud-filtering, and use of data assimilation techniques for validation purposes. The availability of nadir radiances measured by the IMG instrument allowed us to test the tools under development on real data. This paper summarizes the current status of the work.