Apports du sondage infrarouge à l'étude des aérosols atmosphériques

Pour obtenir les articles associés à la thèse, vous pouvez me contacter par email : [email protected] 2001 report from the Intergovernmental Panel on Climate Change emphasized the very low levelof understanding of atmospheric aerosol effects on climate. These particles originate either fromnatural sources (dust, volcanic aerosols...) or from anthropogenic sources (sulfates, soot...). They areone of the main sources of uncertainty on climate change, partly because they show a very highspatio-temporal variability. Observation from space, being global and quasi-continuous, is therefore afirst importance tool for aerosol studies.Remote sensing in the visible domain has been widely used to obtain a better characterization of theseparticles and their effect on solar radiation. On the opposite, remote sensing of aerosols in the infrareddomain still remains marginal. Yet, not only the knowledge of the effect of aerosols on terrestrialradiation is needed for the evaluation of their total radiative forcing, but also infrared remote sensingprovides a way to retrieve other aerosol characteristics (observations are possible at night and day,over land and sea).In this PhD dissertation, we show that aerosol optical depth, altitude and size can be retrieved frominfrared sounder observations. We first study the sensitivity of aerosol optical properties to theirmicrophysical properties, we then develop a radiative transfer code for scattering medium adapted tothe very high spectral resolution of the new generation sounder NASA-Aqua/AIRS, and we finallyfocus on the inverse problem. The applications shown here deal with Pinatubo stratospheric volcanicaerosol, observed with NOAA/HIRS, and with the building of an 8 year climatology of dust over seaand land from this sounder. Finally, from AIRS observations, we retrieve the optical depth at 10 μm,the average altitude and the coarse mode effective radius of mineral dust over sea.Le rapport du Groupe Intergouvernemental d'experts sur l'Evolution du Climat de 2001 soulignait leniveau très imparfait de notre compréhension de l'effet des aérosols atmosphériques sur le climat. Cesparticules d'origines naturelles (poussières, aérosols volcaniques...) ou anthropiques (sulfates,suies...) sont une des principales sources d'incertitude sur le changement climatique. Une des raisonsà cela est leur très grande variabilité spatio-temporelle. Par nature globale et quasi-continue,l'observation spatiale des aérosols est donc un outil indispensable à leur étude.Si la télédétection dans le domaine visible s'est beaucoup développée pour permettre de mieuxcaractériser ces particules et leur effet sur le rayonnement solaire, l'utilisation de la télédétection dansle domaine infrarouge est encore sous-exploitée. Or, non seulement la connaissance de l'effet desaérosols sur le rayonnement terrestre est indispensable à l'évaluation de leur forçage radiatif total,mais la télédétection infrarouge permet aussi la mesure de grandeurs inaccessibles à la télédétectionvisible (observations possibles de nuit comme de jour, sur terre comme sur mer).Dans cette thèse, nous montrons que les observations des sondeurs infrarouges permettent decaractériser les aérosols en épaisseur optique infrarouge, en altitude, et en taille. Après une étude de lasensibilité des propriétés optiques des aérosols à leur microphysique, et le développement d'un codede transfert radiatif pour un milieu diffusant adapté à la haute résolution spectrale du sondeur denouvelle génération NASA-Aqua/AIRS, nous abordons le problème inverse. Les applicationsprésentées ici couvrent entre autres les aérosols stratosphériques volcaniques du Pinatubo, observésavec le sondeur NOAA/HIRS, et la construction d'une climatologie de 8 ans des poussièresdésertiques sur mer et sur terre avec ce même instrument. L'inversion des observations AIRS nous apermis ensuite de déterminer l'épaisseur optique à 10 μm, l'altitude moyenne et le rayon effectif dumode grossier des poussières au-dessus des mers

Measurements of stratospheric volcanic aerosol optical depth from NOAA TIROS Observational Vertical Sounder (TOVS) observations

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Averaging Bias Correction for Future IPDA Lidar Mission MERLIN

The CNES/DLR MERLIN satellite mission aims at measuring methane dry-air mixing ratio column (XCH4) and thus improving surface flux estimates. In order to get a 1% precision on XCH4 measurements, MERLIN signal processing assumes an averaging of data over 50 km. The induced biases due to the non-linear IPDA lidar equation are not compliant with accuracy requirements. This paper analyzes averaging biases issues and suggests correction algorithms tested on realistic simulated scenes

Retrieving the effective radius of Saharan dust coarse mode from AIRS

International audienceWe show that the effective radius of the dust coarse mode can be retrieved from Aqua/AIRS observations, using a two step process. First, for each AIRS observation, the dust infrared optical depth, the mean altitude of the dust layer and an estimate of the temperature and water vapor profiles are obtained from 8 spectral channels, using a Look‐Up‐Table approach. Second, the effective radius is obtained from an additional AIRS channel (located at 9.32 μm), selected for its sensitivity to dust particle size and its insensitivity to dust particle shape or to other potential contaminants (ozone, for example). The dust coarse mode effective radius is retrieved from AIRS over the Atlantic Ocean for the period April to June 2003. It compares well with in situ measurements, transport model simulations and sun‐photometer retrievals. We find that the coarse mode effective radius decreases slightly with transport distance, from 2.4 μm to about 2 μ

Probabilistic global maps of the CO 2 column at daily and monthly scales from sparse satellite measurements

International audienceThe column-average dry air-mole fraction of carbon dioxide in the atmosphere (XCO 2) is measured by scattered satellite measurements like those from the Orbiting Carbon Observatory (OCO-2). We show that global continuous maps of XCO 2 (corresponding to level 3 of the satellite data) at daily or coarser temporal resolution can be inferred from these data with a Kalman filter built on a model of persistence. Our application of this approach on 2 years of OCO-2 retrievals indicates that the filter provides better information than a climatology of XCO 2 at both daily and monthly scales. Provided that the assigned observation uncertainty statistics are tuned in each grid cell of the XCO 2 maps from an objective method (based on consistency diagnostics), the errors predicted by the filter at daily and monthly scales represent the true error statistics reasonably well, except for a bias in the high latitudes of the winter hemisphere and a lack of resolution (i.e., a too small discrimination skill) of the predicted error standard deviations. Due to the sparse satellite sampling, the broad-scale patterns of XCO 2 described by the filter seem to lag behind the real signals by a few weeks. Finally, the filter offers interesting insights into the quality of the retrievals, both in terms of random and systematic errors

Development and Validation of an End-to-End Simulator and Gas Concentration Retrieval Processor Applied to the MERLIN Lidar Mission

International audienceIn the context of MERLIN (MEthane Remote LIdar missioN), a French-German spatial lidar mission dedicated to monitoring the atmospheric methane content, two software programs have been developed: LIDSIM (LIDar SIMulator) and PROLID (PROcessor LIDar). The objectives are to assess whether the instrument design meets the performance requirements and to study the sensitivity of this performance to geophysical parameters. LIDSIM is an end-to-end mission simulator and PROLID is a retrieval processor that provides mole fractions of methane in dry air, averaged over an atmospheric column. These two tools are described in this paper. Results of the validation tests and the first full orbit simulations are reported. Merlin target performance does not seem to be reachable but breakthrough performance is reached

An end-to-end simulator and gas concentration retrieval processor applied to the MERLIN lidar mission to check its performance and study its sensitivity to geophysical parameters

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An end-to-end simulator and gas concentration retrieval processor applied to the MERLIN lidar mission to check its performance and study its sensitivity to geophysical parameters

International audienc

Towards IASI-New Generation (IASI-NG): impact of improved spectral resolution and radiometric noise on the retrieval of thermodynamic, chemistry and climate variables

Besides their strong contribution to weather forecast improvement through data assimilation, thermal infrared sounders onboard polar-orbiting platforms are now playing a key role for monitoring atmospheric composition changes. The Infrared Atmospheric Sounding Interferometer (IASI) instrument developed by the French space agency (CNES) and launched by Eumetsat onboard the Metop satellite series is providing essential inputs for weather forecasting and pollution/climate monitoring owing to its smart combination of large horizontal swath, good spectral resolution and high radiometric performance. EUMETSAT is currently preparing the next polar-orbiting program (EPS-SG) with the Metop-SG satellite series that should be launched around 2020. In this framework, CNES is studying the concept of a new instrument, the IASI-New Generation (IASI-NG), characterized by an improvement of both spectral and radiometric characteristics as compared to IASI, with three objectives: (i) continuity of the IASI/Metop series; (ii) improvement of vertical resolution; (iii) improvement of the accuracy and detection threshold for atmospheric and surface components. In this paper, we show that an improvement of spectral resolution and radiometric noise fulfill these objectives by leading to (i) a better vertical coverage in the lower part of the troposphere, thanks to the increase in spectral resolution; (ii) an increase in the accuracy of the retrieval of several thermodynamic, climate and chemistry variables, thanks to the improved signal-to-noise ratio as well as less interferences between the signatures of the absorbing species in the measured radiances. The detection limit of several atmospheric species is also improved. We conclude that IASI-NG has the potential for strongly benefiting the numerical weather prediction, chemistry and climate communities now connected through the European GMES/Copernicus initiative