Lidar beams in opposite directions for quality assessment of Cloud-Aerosol Lidar with Orthogonal Polarization spaceborne measurements

International audienceWe present the "lidar beams in opposite directions" (LIBOD) technique and applications for quality assessment of spaceborne observations made by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite. LIBOD is applicable to standard total backscatter lidar because it does not require a priori knowledge of the particle extinction-to-backscatter ratio. In this paper, we present (i) an objective assessment of the lidar signal quality and representativity of correlative ground-based lidar and CALIOP measurements only using normalized range-corrected lidar signals and (ii) a numerical filtering and optimization technique for reducing the spurious oscillations induced by noisy signal differentiation as needed for retrieval of particle extinction coefficients and extinction-to-backscatter ratio profiles. Numerical simulations and Monte Carlo tests are conducted for assessing the performance of the LIBOD technique. The applications are illustrated with examples of actual correlative 532nm lidar profiles from CALIOP and a groundbased lidar deployed in Tamanrasset in the heart of Sahara in 2006 and near Strasbourg, France, in 2007. © 2010 Optical Society of America

Optical and microphysical parameters of dense stratocumulus clouds during mission 206 of EUCREX '94 as retrieved from measurements made with the airborne lidar LEANDRE 1

International audienceCloud parameters derived from measurements performed with the airborne backscatter lidar LEANDRE 1 during mission 206 of the EUCREX '94 campaign are reported. A new method has been developed to retrieve the extinction coefficient at the top of the dense stratocumulus deck under scrutiny during this mission. The largest extinction values are found to be related to the highest cloud top altitude revealing the small-scale structure of vertical motions within the stratocumulus field. Cloud optical depth (COD) is estimated from extinction retrievals, as well as cloud top and cloud base altitude using nadir and zenith lidar observations, respectively. Lidar-derived CODs are compared with CODs deduced from radiometric measurements made onboard the French research aircraft Avion de Recherche Atmosphérique et de Télédétection (ARAT/F27). A fair agreement is obtained (within 20%) for COD's larger than 10. Our results show the potential of lidar measurements to analyze cloud properties at optical depths larger than 5

La canopée forestière vue par un lidar aéroporté de nouvelle génération

National audienceA newly developed UV lidar aboard an ultralight airplane provides detailed vegetation characterization

Adaptive parametric algorithms for processing coherent doppler-lidar signal

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Lidar and satellite retrieval of dust aerosols over the Azores during SOFIA/ASTEX

International audienceThe synergy between active (airborne lidar) and passive (Meteosat) sensors is achieved with the help of a numerical transport model (TM2z) to derive optical properties of Saharan dust during a long range transport over the Azores. Measurements were taken in June 1992 during the surface of the ocean, fluxes and interaction with the atmosphere campaign, which took place during the Atlantic stratocumulus transition experiment. The dust source is identified to be in north Morocco from a TM2z back-trajectory analysis. Lidar observations over the Azores show that the dust is maintained in multiple thin layers (few hundred meters) up to 5 km altitude after a 4-day transport. Horizontal gradients are less marked, with a typical scale of variation of about 5 km. Lidar inversions yield dust optical thicknesses from 0.1 to 0.16 mainly due to two layers centered at 1.3 and 3.7 km. Since the weather was extremely cloudy over this region, the dust plume was not observable on the coincident Meteosat image. We thus processed the image taken two days earlier that clearly shows a dust plume between Azores and Spain. The Meteosat inversion was constrained by using the airborne lidar measurements in the marine boundary layer. The retrieved dust optical thicknesses are in good agreement with that retrieved from the lidar. Coherence of both lidar and radiometry measurements suggests that such a combined analysis is promising for retrieving the optical thickness of elevated dust layers as well as their spatial extent outside the source region even under cloudy conditions

Tunable diode laser measurement of pressure-induced shift coefficients of CO2 around 2.05?m for Lidar application

International audienceAtmospheric carbon dioxide (CO2) is one of the main contributors to the greenhouse effect. A global monitoring of CO2 from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO2 and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO2 spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO2 molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (2001)III(0000)I band of CO2 at 2.05?m. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients. © 2011 Elsevier Ltd

Synergy between lidar and Meteosat measurements for a Saharan dust event during SOFIA/ASTEX

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Validation of POLDER/ADEOS data using a ground-based lidar network: Preliminary results for cirrus clouds

International audiencePOLDER-1 on board the Japanese ADEOS platform has collected 8 months of data (October 1996 to June 1997). POLDER is a visible radiometer with multi-directional and polarization capabilities. These features allow to obtain information both on cloud thermodynamical phase and cloud altitude. The POLDER cloud algorithms are currently under validation. For cirrus clouds, a validation based on a comparison between cloud properties inferred from POLDER-1 data and cloud properties retrieved from a ground-based lidar network is currently under consideration. In this paper, preliminary comparisons between cloud altitude inferred from POLDER-1 and lidars are presented. These comparisons show an under-estimation of cloud altitude by POLDER-1 for optically thin clouds. A first theoretical analysis based on radiative transfer simulations allows to explain the difference between POLDER and lidar altitudes. Moreover, a preliminary comparison between thermodynamical cloud phase (liquid water / ice) obtained with POLDER-1 and cloud temperature inferred from radiosoundings and cloud altitudes shows that cirrus clouds at temperatures lower than −40°C are correctly identified as ice layers by POLDER-

A synthesis of the Air Pollution over the Paris Region (ESQUIF) field campaign

Tropospheric photooxidant pollution was investigated in detail for the first time over the Paris area during the Air Pollution Over the Paris Region (ESQUIF) project. From 1998 to 2000, 12 intensive observation periods (IOPs) were carried out. They represented various meteorological situations, all leading to strong polluted events over Paris and its surroundings. During these periods, measurements were performed with a new strategy of circular flights around the city, coupled to stations or remote sensing surface measurements. Such data obtained at various altitudes and at different ranges from the city center document the evolution of pollution events on horizontal and vertical scales. In addition, ESQUIF also allowed for the evaluation of models developed in parallel to the project. In this overview, ESQUIF is presented in terms of the set of IOPs. Periods are compared in terms of meteorology and resulting types of pollution episodes. The occurrence of these latter events is discussed in terms of local production and influence of long-range transport. Using both measurements and model simulations, some important results are highlighted, especially concerning accuracy of boundary conditions, processes of mixing within the boundary layer, surface emissions estimation (including biogenic), and photolysis attenuation. Finally, results from data assimilation studies and sensitivity studies using adjoint modeling and a Monte Carlo approach are also presented

Les avions français de recherche atmosphérique et de télédétection : bilan et perspectives

International audienceWe are planning to replace the French airplanes used for atmospheric research and remote sensing, and we wish to describe some of the current systems (aircraft, instrumentation and data processing) and give some examples of their use. The last part of the article looks the future. It is a summary of proposals made by the Scientific Committee for Atmospheric and Remote Sensing Research Aircraft of future needs, and infers the specifications required for the future aircraft and their instrumentation.Alors que nous sommes en train de planifier le remplacement des avions français utilisés par la communauté scientifique en recherche atmosphérique et en télédétection, nous avons voulu présenter un état des lieux montrant les moyens disponibles (les avions, leur instrumentation et leurs filières de traitement des données) et quelques exemples de travaux scientifiques ayant bénéficié de ces outils. La dernière partie de l'article est tournée vers l'avenir. Elle présente une synthèse des travaux prospectifs réalisés par le Conseil scientifique des avions de recherche atmosphérique et de télédétection pour évaluer les besoins futurs de la communauté scientifique et en déduire les qualités et les performances requises pour les futurs avions de recherche et leur instrumentation