A Preliminary Study of CO2 Flux Measurements by Lidar

A mechanistic understanding of the global carbon cycle requires quantification of terrestrial ecosystem CO2 fluxes at regional scales. In this paper, we analyze the potential of a Doppler DIAL system to make flux measurements of atmospheric CO2 using the eddy-covariance and boundary layer budget methods and present results from a ground based experiment. The goal of this study is to put CO2 flux point measurements in a mesoscale context. In June 2007, a field experiment combining a 2-m Doppler Heterodyne Differential Absorption Lidar (HDIAL) and in-situ sensors of a 447-m tall tower (WLEF) took place in Wisconsin. The HDIAL measures simultaneously: 1) CO2 mixing ratio, 2) atmosphere structure via aerosol backscatter and 3) radial velocity. We demonstrate how to synthesize these data into regional flux estimates. Lidar-inferred fluxes are compared with eddy-covariance fluxes obtained in-situ at 396m AGL from the tower. In cases where the lidar was not yet able to measure the fluxes with acceptable precision, we discuss possible modifications to improve system performance

State-space modelling for heater induced thermal effects on LISA pathfinder's test masses

The OSE (Offline Simulations Environment) simulator of the LPF (LISA Pathfinder) mission is intended to simulate the different experiments to be carried out in flight. Amongst these, the thermal diagnostics experiments are intended to relate thermal disturbances and interferometer readouts, thereby allowing the subtraction of thermally induced interferences from the interferometer channels. In this paper we report on the modelling of these simulated experiments, including the parametrisation of different thermal effects (radiation pressure effect, radiometer effect) that will appear in the Inertial Sensor environment of the LTP (LISA Technology Package). We report as well how these experiments are going to be implemented in the LTPDA toolbox, which is a dedicated tool for LPF data analysis that will allow full traceability and reproducibility of the analysis thanks to complete recording of the processes.Postprint (published version

Studying the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST)

At the end of the afternoon, when the surface heat fluxes start to sharply decrease, the CBL turns from a convective well-mixed layer to an intermittently turbulent residual layer overlying a stably-stratified boundary layer. This transition raises several observational and modelling issues. Even the definition of the boundary layer during this period is fuzzy, since there is no consensus on what criteria to use and no simple scaling laws to apply. Yet it plays an important role in such diverse atmospheric phenomena as transport and diffusion of trace constituents or wind energy production. This phase of the diurnal cycle remains largely unexplored, partly due to the difficulty of measuring weak and intermittent turbulence, anisotropy, horizontal heterogeneity, and rapid time changes. The Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) project is gathering about thirty research scientists from the European Union and the United States to work on this issue. A field campaign (BLLAST-FE) is planned for spring or summer 2011 in Europe. BLLAST will utilize these observations, as well as previous datasets, large-eddy and direct numerical simulations, and mesoscale modelling to better understand the processes, suggest new parameterisations, and evaluate forecast models during this transitional period. We will present the issues raised by the late afternoon transition and our strategy to study it.Peer ReviewedPostprint (published version

Studying the Boundary Layer Late Afternoon nd Sunset Turbulence (BLLAST)

At the end of the afternoon, when the surface heat fluxes start to sharply decrease, the CBL turns from a convective well-mixed layer to an intermittently turbulent residual layer overlying a stably-stratified boundary layer. This transition raises several observational and modeling issues. Even the definition of the boundary layer during this period is fuzzy, since there is no consensus on what criteria to use and no simple scaling laws to apply. Yet it plays an important role in such diverse atmospheric phenomena as transport and diffusion of trace constituents or wind energy production. This phase of the diurnal cycle remains largely unexplored, partly due to the difficulty of measuring weak and intermittent turbulence, anisotropy, horizontal heterogeneity, and rapid time changes. The Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) project is gathering about thirty research scientists from the European Union and the United States to work on this issue. A field campaign (BLLAST-FE) is planned for spring or summer 2011 in Europe. BLLAST will utilize these observations, as well as previous datasets, large-eddy and direct numerical simulations, and mesoscale modeling to better understand the processes, suggest new parameterizations, and evaluate forecast models during this transitional period. We will present the issues raised by the late afternoon transition and our strategy to study it.Peer ReviewedPostprint (published version

The BLLAST field experiment: Boundary-Layer late afternoon and sunset turbulence

Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period. Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.publishedVersio

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Télédétection du CO2 atmosphérique par Lidar DIAL Doppler Hétérodyne à 2 microns.

The first chapter describes the scientific framework of the thesis : atmospheric branch of the carbon cycle, climate change and the Kyoto Protocol, the current monitoring network and major space missions.Le travail de thèse s'organise en plusieurs parties. Le premier chapitre décrit le cadre scientifique dans lequel s'inscrit la thèse : branche atmosphérique du cycle du carbone, changement climatique et protocole de Kyoto, réseau de mesures actuel et principales missions spatiales. Ce chapitre montre notamment comment s'insèrent les différents aspects que j'ai traité pendant la thèse: modélisation, expérimentation et études théoriques dans le cadre plus général de la restitution des flux de surface et de la mesure du C02 atmosphérique. Au final, je m'intéresse plus particulièrement à l'apport scientifique et aux objectifs d'une mesure de C02 atmosphérique par Lidar DIAL à partir de l'espace. Dans le chapitre II, on s'intéresse au domaine d'étude et plus particulièrement à l'évolution du C02 atmosphérique à la méso-échelle. La représentativité temporelle horizontale et verticale d'une mesure de C02 est évaluée dans le but de cadrer l'étude expérimentale. Par ailleurs on y étudie les processus à l'origine de la variabilité du rapport de mélange dans les différentes parties de 1'atmosphère pour mettre au point une méthode de mesure efficace permettant de rendre compte des phénomènes observés. Nous verrons comment cc travail d'étude du C02 atmosphérique à la moyenne échelle a permis, entre autre, de mettre au point une méthode originale de restitution et de caractérisation des flux de surface naturels dans la région du Sud-Ouest parisien. Fort de cette étude et des objectifs de mesure décrits dans le chapitre I, le chapitre III discute la mesure DIAL avant d'en rechercher une optimisation pour obtenir le maximum de précision sur la mesure de concentration. Un soin tout particulier est porté à la spectroscopie, à l'optimisation de paramètre tels que l'épaisseur optique de la colonne d'air sondée et l'énergie des impulsions lasers émises dans l'atmosphère, et à l'analyse des erreurs statistiques et systématiques. Le chapitre IV décrit le système expérimental réalisé au Laboratoire de Météorologie dynamique pendant ces trois années: LIDIA. " Lidar pour la mesure du Dioxyde de carbone Atmosphérique ". Le Lidar DIAL Doppler a été conçu à partir d'un Lidar Doppler déjà existant au Service d'Aéronomie [Bruneau-00, Le Rille-02]. Le chapitre décrit le Lidar, les différentes transformations, les éléments ajoutés et les performances du système global dans le cadre des mesures DIAL. Un intérêt particulier est donné au traitement de signal. Suit alors la partie principale du travail de recherche avec la présentation et la discussion des résultats expérimentaux. Des mesures réalisées de jour et de nuit en fin d'année 2004 et pendant l'année 2005 y sont décrites pour illustrer les différentes possibilités d'une mesure DIAL pour répondre aux objectifs scientifiques décrits dans le chapitre I : mesures intégrées au niveau du sol et validation avec des mesures in-situ, mesures verticales dans la couche limite atmosphérique (CLA), utilisation des cibles nuageuses, mesures dans la troposphère libre et mesures résolues dans la CLA. Nous voyons notamment l'apport de mesures de vent et de vitesses verticales simultanées avec des mesures de concentration pour expliquer les processus naturels ou anthropiques à l'origine de la variation temporelle du rapport de mélange en CO2. Le dernier chapitre s'appuie sur le travail expérimental précédent pour prévoir les performances de futurs systèmes de mesure DIAL aéroporté ou spatial capable de répondre aux objectifs scientifiques à moyen et long terme. Différentes perspectives de travail pour l'amélioration du système expérimental et pour la conception d'un nouveau système y sont abordées. Enfin une conclusion permet de souligner et de rassembler les principaux résultats du travail de thèse

Intérêt du monitorage de la profondeur d'anesthésie par l'entropie spectrale lors de l'intubation orotrachéale dans l'anesthésie pour embolisation d'anévrismes intracrâniens

DIJON-BU Médecine Pharmacie (212312103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF