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3D Monte Carlo Radiative Transfer for Parameter Retrieval in Planetary Atmospheres
No full textInternational audienceRetrieving planetary atmospheric parameters from observational data is particularly challenging under large observation angles, in thick and highly scattering media (such as Titan and Venus), and in the presence of horizontal heterogeneities, like clouds and hazes. Traditional radiative transfer models, often based on plane-parallel or pseudo-spherical approximations, typically assume horizontally homogeneous layers, which limits their applicability in such scenarios.To overcome these limitations, we have developed a novel 3D radiative transfer solver, htrdr-planets, based on the Monte Carlo method that solves models considering spherical and heterogeneous atmospheres[1]. This solver leverages recent advances from the computer graphics and statistical physics communities to ensure computational efficiency.htrdr-planets supports arbitrary ground geometry, represented as triangular meshes with user-defined surface materials, and atmospheric properties defined on unstructured tetrahedral meshes. Gas absorption is modeled using the k-distribution method, and multiple aerosol and cloud populations with their own radiative properties can be described on separate spatial grids.Critically, we address the need for gradients (i.e., sensitivities) in parameter retrieval. Since conventional finite-difference methods are inefficient or infeasible with Monte Carlo, we differentiate the Monte Carlo estimator itself [2]. By reusing the same radiative paths, we construct a Monte Carlo estimator that computes both the radiance and its gradient with respect to atmospheric and surface parameters at negligible additional time cost.We apply this method to Titan and Venus, producing spatially resolved maps of sensitivity with respect to scattering, absorption, and surface-reflection properties. This framework enables retrievals in geometrically complex cases that defy traditional models, including Titan’s polar cloud structure and haze distribution, using Cassini and JWST datasets. This work is supported by the Agence National de la Recherche (ANR) through the RaD3-net project (ANR-21-CE49-0020-01).[1] htrdr-planets, https://www.meso-star.com/projects/htrdr/htrdr.html[2] He, Zili, et al. "Simultaneous Estimation of Radiance and its Sensitivities to Radiative Properties in a Spherical-Heterogeneous Atmospheric Radiative Transfer Model by Monte Carlo: Application to Titan." (Submitted to Journal of Quantitative Spectroscopy and Radiative Transfer.
Projet Plasti-nium (2021-2025) - Flux de microplastiques via les retombées atmosphériques sur Nantes
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Sixth Workshop on Compressible Multiphase Flows - Derivation, Closure laws, Thermodynamics
No full textFine-scale fluctuations of PM 1 , PM 2.5 , PM 10 and SO 2 concentrations caused by a prolonged volcanic eruption (Fagradalsfjall 2021, Iceland)
No full textAbstract. The 2021 Fagradalsfjall fissure eruption was the first of ongoing eruptions in the most densely populated part of Iceland (70 % of population within 50 km). It was monitored by an exceptionally dense reference-grade air quality network (14 stations within 40 km), and the first time that a reference-grade timeseries of PM1 was collected during an eruption. We used these measurements to identify fine-scale dispersion patterns of volcanic air pollutants (SO2, PM1, PM2.5, PM10) in populated areas. Despite its small size the eruption caused a statistically-significant increase in average and peak PM and SO2 concentrations in at least 300 km distance. Peak daily-means of PM1 peak rose to 18–20 µg/m3 from 5–6 µg/m3; and proportion of PM1 increased relative to coarser PM fractions (21–24 % of PM10 compared to 14 % background). Eruption increased PM10 and PM2.5 by ~50 % in populated areas with low background concentrations, but its impact was not measurable in areas with high background sources. This suggests that ash-poor eruptions are one of, or the most, important source of PM1 in Iceland, and potentially in other areas exposed to volcanic emissions. There were significant fine-scale temporal (≤1 hour) and spatial (<1 km) fluctuations in volcanic pollutant concentrations. In Reykjavík, two stations located <1 km of each other recorded peak hourly-mean concentrations of 480 and 250 µg/m3 SO2, and 5 and 0 exceedance events, respectively, within a ~12-hour plume advection event. This has implications for population exposures estimates
Database on bacterial OTUs (V3-V5) on graves in Père Lachaise Cemetery, Paris, France
No full textInternational audienceThis database includes all FASTQ files for bacterial OTUs V3-V5 collected from graves in Père Lachaise Cemetery and a txt file explaining the date and method of sampling, the stone type of the grave and the GPS coordinates. You can find more details in Paloma Reboah's thesis. https://hal.science/tel-04777374 List of primers used V3-V5 5':GGAAGTAAAAGTCGTAACAAGG3':GCTGCGTTCTTCATCGATG
nextGEMS: entering the era of kilometer-scale Earth system modeling
No full textInternational audienceAbstract. The Next Generation of Earth Modeling Systems (nextGEMS) project aimed to produce multidecadal climate simulations, for the first time, with resolved kilometer-scale (km-scale) processes in the ocean, land, and atmosphere. In only 3 years, nextGEMS achieved this milestone with the two km-scale Earth system models, ICOsahedral Non-hydrostatic model (ICON) and Integrated Forecasting System coupled to the Finite-volumE Sea ice-Ocean Model (IFS-FESOM). nextGEMS was based on three cornerstones: (1) developing km-scale Earth system models with small errors in the energy and water balance, (2) performing km-scale climate simulations with a throughput greater than 1 simulated year per day, and (3) facilitating new workflows for an efficient analysis of the large simulations with common data structures and output variables. These cornerstones shaped the timeline of nextGEMS, divided into four cycles. Each cycle marked the release of a new configuration of ICON and IFS-FESOM, which were evaluated at hackathons. The hackathon participants included experts from climate science, software engineering, and high-performance computing as well as users from the energy and agricultural sectors. The continuous efforts over the four cycles allowed us to produce 30-year simulations with ICON and IFS-FESOM, spanning the period 2020–2049 under the SSP3-7.0 scenario. The throughput was about 500 simulated days per day on the Levante supercomputer of the German Climate Computing Center (DKRZ). The simulations employed a horizontal grid of about 5 km resolution in the ocean and 10 km resolution in the atmosphere and land. Aside from this technical achievement, the simulations allowed us to gain new insights into the realism of ICON and IFS-FESOM. Beyond its time frame, nextGEMS builds the foundation of the Climate Change Adaptation Digital Twin developed in the Destination Earth initiative and paves the way for future European research on climate change
Impact de la certification foncière sur les pratiques agricoles et l'environnement à partir de données satellitaires : Cas des Plans Fonciers Ruraux (PFR) au Bénin
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/615837/) * Autres projets (id;sigle;titre): ;OBSYDYA;(EU) Observatoire pilote des paysages et des dynamiques agricoles du Bénin// ;DeSIRA;(EU) Development Smart Innovation through Research in Agriculture//International audienceL'accès à la terre est au coeur de la lutte contre la pauvreté, et sa sécurisation demeure déterminante. En Afrique subsaharienne, plusieurs pays ont mis en place des programmes de formalisation des droits fonciers coutumiers afin de renforcer la stabilité sociale, la sécurité alimentaire et la gestion durable des ressources naturelles. Au Bénin, les Plans Fonciers Ruraux (PFR), ont ainsi permis la certification des droits fonciers dans 300 villages dans les années 2010 et 2011. L'impact des PFR sur les pratiques agricoles reste difficile à documenter et, compte tenu de la forte dépendance des résultats au contexte local, une évaluation rigoureuse est nécessaire pour orienter les politiques publiques. Dans le travail consacré à l'analyse de l'impact des PFR sur les pratiques agricoles et les espaces naturels au Bénin, les données agro-socio-économiques et les produits dérivés d'imagerie satellitaire (cartes d'occupation des sols issues d'images à haute et très haute résolution, ex. Sentinel-2, SPOT6/7) ont été combinés, afin d'identifier des indicateurs permettant d'éclairer les changements intervenus au sein des terroirs villageois. La méthodologie a consisté à une analyse comparative entre villages certifiés PFR et villages non certifiés, portant sur l'organisation spatiale de l'espace cultivé (cultures annuelles et ligneuses) et naturel en 2023 et éclairant sur les impacts à long terme des PFR à partir d'indicateurs de proportions et de métriques paysagères (compacité, fragmentation). Les résultats ont montré une augmentation des plantations et la fragmentation de l'espace cultivé dans les parcelles PFR par rapport aux villages non-PFR, ce qui a reflété à la fois un accroissement des investissements et une diminution de l'intensification agricole (jachère). Ces résultats ouvrent des perspectives pour une analyse plus approfondie de l'impact des PFR sur la sécurité alimentaire. Des études comparatives avant/après PFR basées sur les cartes d'occupation des sols, l'analyse des changements à partir d'indicateurs spatio-temporels dérivés d'images satellitaires MODIS (haute résolution et profondeur temporelle), ainsi que l'intégration des tendances issues des enquêtes de ménages, sont en cours afin de mieux objectiver l'impact des PFR au Bénin
Impact des ruptures de fils sur le comportement mécanique des câbles de précontrainte extérieure
No full textInternational audienceExternal prestressing is a construction technique widely employed since the 1980s for large civil engineering structures to reduce the cross-sectional area of structures and thus their permanent load, and more recently to reinforce structures. External prestressing tendons are composed of strands, each comprising 7 wires with a very high elastic limit, laid in a HDPE sheath, anchored in reinforced concrete blocks and generally tensioned to 80% (excluding creep and shrinkage) of their ultimate tensile strength. To safeguard the cables, grout was injected into the sheaths. However, this protection system has not always prevented the corrosion of the strands. When wires and strands re-anchor through friction in the grout after fracturing due to corrosion, the stress on the remaining tendon increases until the breaking load of the entire tendon is reached. The sudden release of energy from such a break can jeopardize the structure and endanger any personnel present on-site.Therefore, understanding the state of the cable at a given level of degradation and the permissible degradation before failure is crucial for structure managers.Several 46 m long cables between supports were tested and brought to failure by the progressive cutting of the wires composing the strands. Initially, three tendons, each comprising a single strand of seven wires, were tested. Subsequently, three tendons, each comprising five strands, were examined.The experiments conducted and the analysis of the results have enhanced the understanding of the evolution of tension in the tendon as it becomes damaged. To this end, a model was developed to estimate the length affected by wire ruptures. This work also presents findings regarding the transfer of stresses within the tendon and strands resulting from these ruptures.Finally, a model that estimates tension loss due to the sliding of wires after they break is presented.La précontrainte extérieure est une technique de construction largement employée depuis les années 1980 pour les grands ouvrages de génie civil afin de réduire la section des structures et donc leur charge permanente, et plus récemment pour renforcer des structures. Les câbles de précontrainte extérieure sont composés de torons, chacun comprenant 7 fils à très haute limite élastique, disposés dans une gaine en PEHD, ancrés dans des blocs de béton armé et généralement tendus à 80% (hors fluage et retrait) de leur résistance à la traction ultime. Pour protéger les câbles, du coulis a été injecté dans les gaines. Cependant, ce système de protection n'empêché pas toujours la corrosion des torons. Lorsque les fils et les torons, après rupture due à la corrosion, se réancrent par frottement dans le coulis, la contrainte dans la partie saine du câble augmente jusqu'à ce que la charge de rupture de l'ensemble du câble soit atteinte. La libération soudaine d'énergie lors d'une telle rupture peut mettre en péril la structure et mettre en danger le personnel présent sur site. Par conséquent, la compréhension de l'état du câble à un niveau de dégradation donné et de la dégradation admissible avant rupture est cruciale pour les gestionnaires d'ouvrages. Plusieurs câbles de 46 m de long entre appuis ont été testés et amenés à la rupture par découpe progressive des fils composant les torons. Dans un premier temps, trois câbles, comprenant chacun un seul toron de sept fils, ont été testés. Par la suite, trois câbles, comprenant chacun cinq torons, ont été examinés. Les expérimentations menées et l'analyse des résultats ont permis d'améliorer la compréhension de l'évolution de la tension dans le câble au fur et à mesure de son endommagement. À cette fin, un modèle a été développé pour estimer la longueur affectée par les ruptures de fils. Ce travail présente également des résultats concernant le transfert des contraintes au sein du câble et des torons résultant de ces ruptures. Enfin, un modèle estimant la perte de tension due au glissement des fils après leur rupture est présenté
Dissecting cirrus clouds: navigating effects of turbulence on homogeneous ice formation
No full textInternational audienceTurbulent air motions determine the local environment in which cloud ice crystals form. Homogeneous freezing of aqueous solution droplets is the most fundamental pathway to nucleate ice crystals in cirrus. Lack of knowledge about the role of turbulence in cirrus ice formation limits our understanding of how uncertainties in small-scale cloud processes affect the climatological radiative effect of cirrus. Here we shed first light on how turbulent fluctuations in temperature and supersaturation interact with probabilistic homogeneous freezing. We show that spatial model resolution substantially below 1-10 m is needed to properly simulate homogeneous freezing events. Importantly, microscale turbulence generates large variability in nucleated ice crystal number concentrations. Previous research ascribed this variability to mesoscale dynamical forcing due to gravity waves alone. The turbulence-generated microphysical variability has macrophysical implications. The wide range of predicted cloud radiative heating anomalies in anvil cirrus due to turbulence-ice nucleation interactions, comparable to typical mean values, is potentially large enough to affect the response of tropical cirrus cloud systems to global warming. Our results have ramifications for the multiscale modeling of cirrus clouds and the interpretation of in situ measurements
Can Households Drive the Energy Transition?
No full textTo accelerate the energy renovation of buildings necessary to achieve carbon neutrality by 2050, the French government has launched an energy renovation plan for buildings. This plan allocates funds across various subsidy and aid mechanisms for housing renovation. What is the impact of these investment subsidies for energy retrofit on such investment and on the consumption and savings of a homeowner household that is not in fuel poverty? How much subsidy is needed to make homes energy efficient? To answer these questions, we develop a two-period, two-goods model that incorporates "essential baskets", i.e., baskets of goods (with a "minimum energy" level and an "essential composite good"). Investment subsidy for energy retrofit is effective if it is targeted and, this targeting should not be based solely on income. Indeed, we highlight non-monetary side effects as one of the key parameters of policy effectiveness. To be effective and as inexpensive as possible for public authorities, subsidies must depend not only on household income, but also on the cost of the work and therefore on the condition of the housing before the work is carried out. For illustrative purposes, we estimate and calibrate the parameters of the model with data from French households that only use electricity as an energy source for their homes. We determine the subsidies that encourage households to renovate their homes to make them more energy efficient