LOA - Laboratoire d'Optique Atmosphèrique - UMR 8518

France Centre de recherche public
Accréditation CIR
Contact principal
Téléphone : 33(0)3 20 43 45 32
Mail : direction-loa@univ-lille1.fr
Adresse :
Bât. P5
59655 Villeneuve d'Ascq
France
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Description
(Extrait du site web)
Activité Générale :

L'optique atmosphérique cherche à modéliser la propagation à travers l'atmosphère de la lumière visible reçue du soleil et de la lumière infrarouge émise par l'ensemble des surfaces et de l'atmosphère terrestres. Les travaux menés au LOA dans ce domaine s'insèrent dans l'étude globale du climat.

Un premier objectif est de quantifier le rôle de ce rayonnement visible et infrarouge dans les échanges énergétiques de la planète, en particulier de préciser le rôle des nuages dans le bilan radiatif de la terre dont ils constituent un facteur essentiel.

Un second axe de recherche porte sur la caractérisation à l'échelle du globe de différents paramètres qui sont en relation directe avec l'évolution climatique (nuages, aérosols, surfaces), en utilisant principalement l'observation satellitaire.
Les travaux menés dans ce contexte mettent en oeuvre:

* La conception de logiciels permettant de simuler le transfert du rayonnement, à l'aide de modèles du système terre - atmosphère.
* L'analyse d'observations acquises par les capteurs satellitaires existants, le plus souvent sous forme d'images traitées sur ordinateur, et la conception d'expériences satellitaires nouvelles.
* La réalisation de campagnes d'observation de terrain, utilisant des appareillages développés par le laboratoire, mis en oeuvre au sol ou à partir d'avions ou de ballons stratosphériques, et destinés à valider les modèles ou à mettre en évidence les processus atmosphériques.

Le LOA est une unité Mixte de Recherches (UMR/CNRS 8518). Il fait partie de la Fédération de Recherches (FR1818) Milieux naturels et anthropisé Flux et dynamique.

Quelques documents de Laboratoire d'Optique Atmosphèrique
Indirect radiative forcing due to aerosols over the North Atlantic region.
ACE-2: CLOUDYCOLUMN
1996 - 1998

Sujets :
Environmental Protection, Meteorology
Participants :
Laboratoire d'Aérologie
Laboratoire d'Aérologie


Laboratoire de Météorologie Physique
Laboratoire de Météorologie Physique


Laboratoire d'Optique Atmosphèrique
Laboratoire d'Optique Atmosphèrique


German Aerospace Center
German Aerospace Center


Secretary of State for Defence - Ministry of Defence
Secretary of State for Defence - Ministry of Defence


Freie Universitaet Berlin
Freie Universitaet Berlin


University of Manchester Institute of Science and Technology (umist)
University of Manchester Institute of Science and Technology (umist)


CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE FRANCE
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
Research

URA 1357 - GROUPE D'ETUDE DE L'ATMOSPHRE MTOROLOGIQUE - GAME Avenue Gustave Coriolis 42, C.N.R. MTtTorologique 31057
FRANCE
FREIE UNIVERSITAET BERLIN DEUTSCHLAND
FREIE UNIVERSITAET BERLIN
Education

INSTITUT FUER WELTRAUMWISSENSCHAFTEN (WE4) - FACHBEREICH GEOWISSENSCHAFTEN Fabeckstrasse 69 14195
DEUTSCHLAND
SECRETARY OF STATE FOR DEFENCE - MINISTRY OF DEFENCE UNITED KINGDOM
SECRETARY OF STATE FOR DEFENCE - MINISTRY OF DEFENCE
Research,Other

METEOROLOGICAL OFFICE FLIGHT RESEARCH D.E.R.A. Aerospace, Building Y 46 GU14 0LX
UNITED KINGDOM
University of Manchester Institute of Science and Technology (UMIST) UNITED KINGDOM
University of Manchester Institute of Science and Technology (UMIST)
Education

Department of Pure and Applied Physics Physics Department PO Box 88 Sackville Street M60 1QD
UNITED KINGDOM
Hide objectives
Cloudy-Column is one of five projects which constitute the European contribution to the second Aerosol Characterisation Experiment (ACE-2) of the International Global Atmospheric Chemistry Project (IGAC). Cloudy-Column is specifically dedicated to the study of the indirect effect. The objective is to develop parameterisations of marine extended stratocumulus for climate models, that include explicitly the characteristics of the aerosol background and their effects on cloud radiative properties.

Source : Cordis  

Cloud detection and derivation of cloud properties from POLDER
1997
Auteurs : Jean-Claude BURIEZ, B. Bonnel, P. Couvert, Pierre Couvert, Y. FOUQUART, M. HERMAN, Frédéric PAROL, Goloub PHILLIPPE, D. G. SEZE, D. G. SEZE et Claudine VANBAUCE
Masquer le résumé
POLDER (POLarization and Directionality of the Earth's Reflectances) is a new instrument devoted to the global observation of the polarization and directionality of solar radiation reflected by the Earth surface-atmosphere system. This radiometer has been on board the Japanese ADEOS platform since August 1996. This paper describes the main algorithms of the POLDER 'Earth radiation budget (ERB) & clouds' processing line used to derive products on a routine basis in the early phase of the mission. In addition to the bidirectional reflectance and polarization distribution functions, the main products will be the cloud optical thickness, pressure (from two different methods) and thermodynamic phase. Airborne POLDER observations support the present algorithms for the cloud detection and the derivation of cloud properties.
Keywords :
Clouds ; Satellite observation ; Solar radiation ; Algorithm ; Radiation polarization ; Reflectance ; Optical thickness ; Thermodynamic parameter ; Spaceborne instruments ;
Source : Pascal - INIST  

Mineralogy of Saharan dust transported over northwestern tropical Atlantic Ocean in relation to source regions
2002
Auteurs : Sandrine Caquineau, Annie Gaudichet, Annie Gaudichet, Laurent Gomes, Gilet L., Michel LEGRAND et M. Legrand
Masquer le résumé
[1] On the basis of daily Saharan dust samples collected at Sal Island (Cape Verde Archipelagos) and Barbados (Caribbean Sea) over 3 years, this study focuses on the mineralogical signature of the African sources providing dust over the tropical North Atlantic Ocean. First, the sources of the collected dust were localized by using relative clays abundance (illite-to-kaolinite ratio) combined with Meteosat infrared imagery, horizontal visibility, and backward trajectories of dusty air masses. Then, each identified source was linked to a single value of the illite-to-kaolinite ratio. Those results highlight that the clay content of the emitted dust depends directly on both the latitude and the longitude of the source. Dust originating from northwestern sources exhibits illite-to-kaolinite ratios higher than those from Sahelian regions. Likewise, illite-to-kolinite ratio decreases from west to east.
Keywords :
America ; Central America ; West Indies ; Atlantic Ocean Islands ; Atlantic Ocean ; Meteosat satellites ; Caribbean Sea ; Barbados ; Cape Verde Islands ; Tropical Atlantic Ocean ; Inorganic compound ; Image analysis ; Satellite observation ; Atmospheric dust ; Air mass ; Trajectory ; Infrared imaging ; Mineralogy ;
Source : Pascal - INIST  

Large-scale analysis of cirrus clouds from AVHRR data : Assessment of both a microphysical index and the cloud-top temperature
1997
Auteurs : Jean-Claude BURIEZ, Y. FOUQUART, V. GIRAUD, Frédéric PAROL et G. Sèze
Masquer le résumé
An algorithm that allows an automatic analysis of cirrus properties from Advanced Very High Resolution Radiometer (AVHRR) observations is presented. Further investigations of the information content and physical meaning of the brightness temperature differences (BTD) between channels 4 (11 μm) and 5 (12 μm) of the radiometer have led to the development of an automatic procedure to provide global estimates both of the cirrus cloud temperature and of the ratio of the equivalent absorption coefficients in the two channels, accounting for scattering effects. The ratio is useful since its variations are related to differences in microphysical properties. Assuming that cirrus clouds are composed of ice spheres, the effective diameter of the particle size distribution can be deduced from this microphysical index. The automatic procedure includes first, a cloud classification and a selection of the pixels corresponding to the envelope of the BTD diagram observed at a scale of typically 100 X 100 pixels. The classification, which uses dynamic cluster analysis, takes into account spectral and spatial properties of the AVHRR pixels. The selection is made through a series of tests, which also guarantees that the BTD diagram contains the necessary information, such as the presence of both cirrus-free pixels and pixels totally covered by opaque cirrus in the same area. Finally, the cloud temperature and the equivalent absorption coefficient ratio are found by fitting the envelope of the BTD diagram with a theoretical curve. Note that the method leads to the retrieval of the maximum value of the equivalent absorption coefficient ratio in the scene under consideration. This, in turn, corresponds to the minimum value of the effective diameter of the size distribution of equivalent Mie particles. The automatic analysis has been applied to a series of 21 AVHRR images acquired during the International Cirrus Experiment (ICE'89). Although the dataset is obviously much too limited to draw any conclusion at the global scale, it is large enough to permit derivation of cirrus properties that are statistically representative of the cirrus systems contained therein. The authors found that on average, the maximum equivalent absorption coefficient ratio increases with the cloud-top temperature with a jump between 235 and 240 K. More precisely, for cloud temperatures warmer than 235 K, the retrieved equivalent absorption coefficient ratio sometimes corresponds to very small equivalent spheres (diameter smaller than 20 μm). This is never observed for lower cloud temperatures. This change in cirrus microphysical properties points out that ice crystal habits may vary from one temperature regime to another. It may be attributed to a modification of the size and/or shape of the particles.
Keywords :
Cirrus ; Physical parameter ; Automatic analysis ; Algorithm ; Image analysis ; Absorptance ; Brightness temperature ; Temperature difference ; Classification ; Particle size ;
Source : Pascal - INIST  

Cirrus microphysical properties and their effect on radiation : survey and integration into climate models using combined satellite observations (CIRAMOSA)
CIRAMOSA
2001 - 2003

Sujets :
Measurement Methods, Environmental Protection, Resources of the Sea, Fisheries, Meteorology, Forecasting
Participants :
Laboratoire de Météorologie Dynamique
Laboratoire de Météorologie Dynamique


Laboratoire d'Optique Atmosphèrique
Laboratoire d'Optique Atmosphèrique


Centre National de la Recherche Scientifique
Centre National de la Recherche Scientifique


Secretary of State for Defence - Ministry of Defence
Secretary of State for Defence - Ministry of Defence


CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE FRANCE
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
Research

URA 0713 - LABORATOIRE D'OPTIQUE ATMOSPHÉRIQUE Laboratoire d'Optique Atmosphérique (URA 713) UER de Physique Fondamentale Université de Lille 59655
FRANCE
SECRETARY OF STATE FOR DEFENCE - MINISTRY OF DEFENCE UNITED KINGDOM
SECRETARY OF STATE FOR DEFENCE - MINISTRY OF DEFENCE
Research

METEOROLOGICAL OFFICE HADLEY CENTRE FOR CLIMATE PREDICTION AND RESEARCH Fitzroy Road, Metz Office EX1 3PB
UNITED KINGDOM
Hide objectives
The radiation effect due to changes of microphysical properties within cirrus clouds can be very important. We will provide a long-term survey of these properties, together with cirrus macrophysical properties, and then establish a compilation of correlations between them and the state of the atmosphere. This information is essential for the understanding of changes in clouds expected by a global climate change. Satellite instruments measuring radiation with a good spectral resolution as well as multi-angular measurements of polarized reflectance used with newly developed retrieval algorithms are now capable to give this information over the whole globe. Extensive care will be taken of the validation of the retrieved cirrus properties by intercomparison with data sets from regional measurement campaigns. Models for climate prediction can profit from the outcome of this proposal by using the most appropriate correlations in their radiation codes.

Source : Cordis  

Remote sensing of aerosols over boreal forest and lake water from AVHRR data
1997
Auteurs : N. T. O'NEILL, A. ROYER, V. SOUFFLET et Didier TANRE
Masquer le résumé
A complete set of advanced very high resolution radiometer (AVHRR) data and ground-based measurements of aerosol and water-vapor content are used to test an algorithm for the retrieval of aerosol properties over dense vegetation in the red and over lake water in both the red and the near-infrared AVHRR channels. With the assumptions of a weak and reasonably constant surface reflectance and an appropriate aerosol model in the radiative transfer code, the remaining variance in the satellite signal is interpreted in terms of aerosol optical thickness. From theoretical computations, it appears that the algorithm is particularly sensitive to the surface albedo and that an uncertainty of 0.01 in reflectance leads to an error of ±0.1 in the retrieved optical thickness. This theoretical estimate is confirmed by data acquired over a boreal forest region in Canada and over one of the Great Lakes (Ontario). In particular, channel 1 observations over vegetation in the forward scattering direction are well suited for retrievals because vegetation pixels appear darker owing to shadowing effects. Conversely, the forward scattering geometry over lakes introduces large errors in both channels owing to specular reflections (glint effects). Even for observations well removed from the forward scattering principal plane, lake surface reflections clue to sky radiance glint have to be taken into account. Because the accuracy of the retrieval algorithm is affected by water-vapor absorption in channel 2 and by variations in lake-water turbidity in channel 1, the optimal retrieval configuration is to employ vegetation observations in channel 1. Bidirectional effects have to be considered, however, for observations in the backscatter direction.
Keywords :
Remote sensing ; Aerosols ; Taiga ; Lake Ontario ; Vegetation index ; Humidity ; Spectral properties ; Pixel ; Radiative transfer ; AVHRR radiometer ; Great Lakes of America ; North America ; America ; Multispectral scanner ;
Source : Pascal - INIST  

Ground measurements of the polarized bidirectional reflectance of snow in the near-infrared spectral domain : Comparisons with model results
1998
Auteurs : J.-L. Deuzé, M. FILY, Michel Fily, C. LEROUX, C. Leroux, Goloub PHILLIPPE, C. SERGENT et C. SERGENT
Masquer le résumé
Ground-based measurements were carried out in the French Alps in March 1995 to study the bidirectional and polarized bidirectional reflectances of various snow covers. Atmospheric (optical thickness) and snow characteristics (grain size and type) were measured simultaneously. The ground reflectance data are compared with snow reflectance modeling results. A radiative transfer model based on the adding-doubling method is used to compute the snow reflectance. The single-scattering parameters are determined by a Mie or a ray-tracing code depending on the particle shape introduced in the model (spherical or hexagonal ice particles). Special attention is paid to the comparisons in the near-infrared spectral range (1.65 μm) because of the sensitivity of snow reflectance to the grain size and shape. In the visible and near-infrared domains of the solar spectrum, the amplitude of the polarized signal is very low and independent of the snow grain size. The agreement between measurements and model results is good if hexagonal particles are introduced in the model instead of the spherical snow grains commonly used in reflectance studies.
Keywords :
Snow cover ; Ground based measurement ; Solar radiation ; Radiation polarization ; Polarimetry ; Near infrared spectrum ; Reflectance ; Radiative transfer ; Observation data ; Comparative study ; Particle shape ; Grain size ; Alps ; France ; Bidirectional reflectance model ; Europe ;
Source : Pascal - INIST  





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