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Journal articles on the topic "Observations par sodar"
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Trotta, Domenico, Andrew P. Dimmock, Xochitl Blanco-Cano, Robert J. Forsyth, Heli Hietala, Naïs Fargette, Andrea Larosa, et al. "Observation of a Fully-formed Forward–Reverse Shock Pair due to the Interaction between Two Coronal Mass Ejections at 0.5 au." Astrophysical Journal Letters 971, no. 2 (August 1, 2024): L35. http://dx.doi.org/10.3847/2041-8213/ad68fa.
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Abstract We report direct observations of a fast magnetosonic forward–reverse shock pair observed by Solar Orbiter on 2022 March 8 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions, is due to the interaction between two successive coronal mass ejections (CMEs), never previously observed to give rise to a forward–reverse shock pair. The scenario is supported by remote observations from extreme ultraviolet cameras and coronagraphs, where two candidate eruptions compatible with the in situ signatures have been found. In the interaction region, we find enhanced energetic particle activity, strong nonradial flow deflections, and evidence of magnetic reconnection. At 1 au, well radially aligned Wind observations reveal a complex event, with characteristic observational signatures of both stream interaction region and CME–CME interaction, thus demonstrating the importance of investigating the complex dynamics governing solar eruptive phenomena.
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Wang, Mingming, and Leiming Zhang. "Synchronous Changes of GPP and Solar-Induced Chlorophyll Fluorescence in a Subtropical Evergreen Coniferous Forest." Plants 12, no. 11 (June 5, 2023): 2224. http://dx.doi.org/10.3390/plants12112224.
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Using in situ near-surface observations of solar-induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) of a subtropical evergreen coniferous forest in southern China, this study analyzed the dynamics of SIF, GPP and their environmental responses, and explored the potential of SIF in characterizing the variation of GPP. The results showed that SIF and GPP have similar diurnal and seasonal variation and both reach the highest value in summer, indicating that the SIF can be applied to indicate the seasonal variation of GPP for the subtropical evergreen co-niferous. With the increase in temporal scale, the correlation between SIF and GPP becomes more linear. The diurnal variations of both SIF and GPP were characterized by photosynthetically active radiation (PAR), the seasonal variations of SIF and GPP were influenced by air temperature (Ta) and PAR. Probably due to the absent of drought stress during the study period, no significant correlation was detected between soil water content (SWC) and either SIF or GPP. With the in-crease in Ta, PAR or SWC, the linear correlation between the SIF and GPP gradually decreased, and when Ta or PAR was relatively higher, the correlation between SIF and GPP become weakly. Further research is still needed to illustrate the relationship between SIF and GPP under drought condition which occurred frequently in this region based on longer observation.
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Gerland, S., G. E. Liston, J. G. winther, J. B. Ørbæk, and B. V. Ivanov. "Attenuation of solar radiation in Arctic snow: field observations and modelling." Annals of Glaciology 31 (2000): 364–68. http://dx.doi.org/10.3189/172756400781820444.
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AbstractSolar radiation was measured above and in the snowpack on Svalbard using a spectroradiometer and a quantum meter measuring average photosynthetically active radiation (PAR). In order to specify the effect of melting on the snow’s radiation properties, all measurements were performed before and during the melt season in May and June 1997 and 1998. Along with the radiation measurements, physical and structural snow properties were logged in snow pits. A physically based model was used to simulate the penetration of radiation into the snow The model formulation accounts for the spectrally dependent interactions between the radiation and snow grains, and requires inputs of the incoming solar radiation spectrum and the vertical snow density and grain-size. The vertical radiation-flux profile was computed using a two-stream radiation approximation where the absorption and reflection coefficients are related to the surface albedo, solar spectrum, grain-size and number of grains per unit volume. In general, snow before the onset of melt attenuates solar radiation more than coarser-grained snow that has been exposed to melting conditions. Quantum-meter measurements of PAR before and during melt can be explained by model outputs using both constant and variable extinction coefficients. Spectroradiometer measurements at fixed depth levels showed, in addition, that impurities in the snow reduce its transparency and therefore have the opposite effect to aging.
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Joiner, Joanna, Yasuko Yoshida, Philipp Köehler, Petya Campbell, Christian Frankenberg, Christiaan van der Tol, Peiqi Yang, Nicholas Parazoo, Luis Guanter, and Ying Sun. "Systematic Orbital Geometry-Dependent Variations in Satellite Solar-Induced Fluorescence (SIF) Retrievals." Remote Sensing 12, no. 15 (July 22, 2020): 2346. http://dx.doi.org/10.3390/rs12152346.
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While solar-induced fluorescence (SIF) shows promise as a remotely-sensed measurement directly related to photosynthesis, interpretation and validation of satellite-based SIF retrievals remains a challenge. SIF is influenced by the fraction of absorbed photosynthetically-active radiation at the canopy level that depends upon illumination geometry as well as the escape of SIF through the canopy that depends upon the viewing geometry. Several approaches to estimate the effects of sun-sensor geometry on satellite-based SIF have been proposed, and some have been implemented, most relying upon satellite reflectance measurements and/or other ancillary data sets. These approaches, designed to ultimately estimate intrinsic or physiological components of SIF related to photosynthesis, have not generally been applied globally to satellite measurements. Here, we examine in detail how SIF and related reflectance-based indices from wide swath polar orbiting satellites in low Earth orbit vary systematically due to the host satellite orbital characteristics. We compare SIF and reflectance-based parameters from the Global Ozone Mapping Experiment 2 (GOME-2) on the MetOp-B platform and from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel 5 Precursor satellite with a focus on high northern latitudes in summer where observations at similar geometries and local times occur. We show that GOME-2 and TROPOMI SIF observations agree nearly to within estimated uncertainties when they are compared at similar observing geometries. We show that the cross-track dependence of SIF normalized by PAR and related reflectance-based indices are highly correlated for dense canopies, but diverge substantially as the vegetation within a field-of-view becomes more sparse. This has implications for approaches that utilize reflectance measurements to help account for SIF geometrical dependences in satellite measurements. To further help interpret the GOME-2 and TROPOMI SIF observations, we simulated cross-track dependences of PAR normalized SIF and reflectance-based indices with the one dimensional Soil-Canopy Observation Photosynthesis and Energy fluxes (SCOPE) canopy radiative transfer model at sun–satellite geometries that occur across the wide swaths of these instruments and examine the geometrical dependencies of the various components (e.g., fraction of absorbed PAR, SIF yield, and escape of SIF from the canopy) of the observed SIF signal. The simulations show that most of the cross-track variations in SIF result from the escape of SIF through the scattering canopy and not the illumination.
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Bisoi, Susanta Kumar, and P. Janardhan. "Observations of a geomagnetic SI+ – SI− pair and associated solar wind fluctuations." Proceedings of the International Astronomical Union 8, S294 (August 2012): 543–44. http://dx.doi.org/10.1017/s1743921313003141.
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AbstractWe report a pair of oppositely directed sudden impulses (SI), in the geomagnetic field (ΔX), at ground stations, called SI+ – SI− pairs, that occurred between 1835 UT and 2300 UT on 23 April 1998. The SI+ – SI− pair, was well correlated with corresponding variations in the solar wind density, while solar wind velocity and the southward component of the interplanetary magnetic field (Bz) did not show any correspondence. This event had no source on the visible solar disk but was associated with a rear-side fast partial halo coronal mass ejection (CME) and an optically occulted M1.4 class solar flare behind the west limb. This event was unique in that one could clearly identify variations in ΔX at ground stations with solar wind parameters.
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Ren, Xiaoli, Honglin He, Li Zhang, and Guirui Yu. "Global radiation, photosynthetically active radiation, and the diffuse component dataset of China, 1981–2010." Earth System Science Data 10, no. 3 (July 5, 2018): 1217–26. http://dx.doi.org/10.5194/essd-10-1217-2018.
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Abstract. Solar radiation, especially photosynthetically active radiation (PAR), is the main energy source of plant photosynthesis, and the diffuse component can enhance canopy light use efficiency, thus increasing ecosystem productivity. In order to predict the terrestrial ecosystem productivity precisely, we not only need global radiation and PAR as driving variables, but also need to treat diffuse radiation and diffuse PAR explicitly in ecosystem models. Therefore, we generated a series of radiation datasets, including global radiation, diffuse radiation, PAR, and diffuse PAR of China from 1981 to 2010, based on the observations of the China Meteorology Administration (CMA) and the Chinese Ecosystem Research Network (CERN). The dataset should be useful for the analysis of the spatiotemporal variations of solar radiation in China and the impact of diffuse radiation on terrestrial ecosystem productivity based on ecosystem models. The dataset is freely available from Zenodo on the following website: https://zenodo.org/record/1198894#.Wx6–C_MwWo (https://doi.org/10.11922/sciencedb.555, Ren et al., 2018).
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Dorf, M., H. Bösch, A. Butz, C. Camy-Peyret, M. P. Chipperfield, A. Engel, F. Goutail, et al. "Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles." Atmospheric Chemistry and Physics Discussions 5, no. 6 (December 19, 2005): 13011–52. http://dx.doi.org/10.5194/acpd-5-13011-2005.
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Abstract. For the first time, results of all four existing stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO, (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.8)pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument agree to <±50% with the photochemically-corrected balloon observations, and tend to show less agreement below 20 km.
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Bai, Jianhui. "Observations and estimations of PAR and solar visible radiation in North China." Journal of Atmospheric Chemistry 69, no. 3 (September 2012): 231–52. http://dx.doi.org/10.1007/s10874-012-9239-0.
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GUO, Haiqiang. "A dataset of carbon dioxide flux from Chongming Dongtan Wetland of Shanghai during 2004–2010." China Scientific Data 9, no. 1 (March 31, 2024): 1–5. http://dx.doi.org/10.11922/11-6035.csd.2023.0043.zh.
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As one of the standard methods of micrometeorology, eddy covariance technology has become the primary tool for monitoring the exchange of carbon dioxide, water and heat flux between terrestrial ecosystems and the atmosphere. This dataset includes the flux data accumulated by the National Observations and Research Station for Wetland Ecosystems in the Yangtze Estuary, collected in Dongtan Wetland on Chongming Island, Shanghai from September 2004 to December 2010, with a time resolution of half hour, and the data items cover air temperature (T_air), relative humidity (RH), soil temperature (T_soil), photosynthetically active radiation (PAR), solar radiation (Solar), net radiation (Rn), rainfall (Precip), sensible heat flux (Hs), latent heat flux (LE) and net carbon dioxide exchange (NEECO2), etc. The ecosystem observed in this study is typical of subtropical coastal salt marshes, predominantly inhabited by such plants as Phragmites australis and Spartina alterniflora. The observation system setup, equipment maintenance, data processing and quality control follows FLUXNET recommended protocols, ensuring high data reliability. The dataset can provide solid data support for the carbon budget, blue carbon estimation and biological invasion impact assessment of China's coastal salt marshes.
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Cubas Armas, Melania, and Damian Fabbian. "Do MURaM and STAGGER Simulations of Solar Faculae Match Observational Signatures from Magnetic Structures?" Astrophysical Journal 923, no. 2 (December 1, 2021): 207. http://dx.doi.org/10.3847/1538-4357/ac2605.
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Abstract We compare results of simulations of solar facular-like conditions performed using the numerical codes MURaM and STAGGER. Both simulation sets have a similar setup, including the initial condition of ≈200 G vertical magnetic flux. After interpolating the output physical quantities to constant optical depth, we compare them and test them against inversion results from solar observations. From the snapshots, we compute the monochromatic continuum in the visible and infrared, and the full Stokes vector of the Fe i spectral line pair around 6301–6302 Å. We compare the predicted spectral lines (at the simulation resolution and after smearing to the HINODE SP/SOT resolution) in terms of their main parameters for the Stokes I line profiles, and of their area and amplitude asymmetry for the Stokes V profiles. The codes produce magnetoconvection with similar appearance and distribution in temperature and velocity. The results also closely match the values from recent relevant solar observations. Although the overall distribution of the magnetic field is similar in both radiation-magnetohydrodynamic (RMHD) simulation sets, a detailed analysis reveals substantial disagreement in the field orientation, which we attribute to the differing boundary conditions. The resulting differences in the synthetic spectra disappear after spatial smearing to the resolution of the observations. We conclude that the two sets of simulations provide robust models of solar faculae. Nevertheless, we also find differences that call for caution when using results from RMHD simulations to interpret solar observational data.
Dissertations / Theses on the topic "Observations par sodar"
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Aligné, Thomas. "Assimilation variationnelle des observations de sondeurs infrarouges hyperspectraux : correction de biais et la détection nuageuse." Toulouse 3, 2007. http://www.theses.fr/2007TOU30038.
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L'objectif de cette thèse est d'optimiser les méthodes d'assimilation de données pour l'utilisation des sondeurs infrarouges hyperspectraux. Le travail se concentre sur deux aspects essentiels : la correction de biais et la détection nuageuse. La correction de biais est une étape nécessaire qui consiste à réduire les erreurs systématiques des observations. On présente la correction de biais variationnelle (VarBC) qui est moins sensible à une contamination par les biais du modèle de prévision. Cette propriété est exploitée pour paramétriser de manière objective les biais. La détection nuageuse élimine les observations contaminées par les nuages. On identifie une boucle d'interaction entre la correction de biais et la détection nuageuse. Une nouvelle métrique permet de réduire sensiblement son impact sur l'analyse. Un nouveau schéma de détection des nuages est introduit puis validé pour des observations simulées et réelles. Il ouvre une voie vers l'assimilation des observations nuageuses.
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Pangaud, Thomas. "Assimilation des radiances des sondeurs infrarouges hyperspectraux en condition nuageuse : application à des cyclogénèses extratropicales." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/772/.
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L'objectif de cette thèse est de proposer une méthode d'assimilation des observations des sondeurs infrarouges hyperspectraux en condition nuageuse. Ces observations étaient jusqu'à présent rejetées des modèles d'assimilation en raison de la nature complexe des nuages et de leursprocessus non-linéaires évoluant dans des échelles spatio-temporelles généralement inférieures à celle du modèle. L'émergence des techniques variationnelles ainsi que les améliorations réalisées en matière de modélisation nuageuse et de transfert radiatif ont relancé l'intérêt de la communauté scientifique pour l'assimilation des radiances nuageuses. Ces dernières représentent en effet une large majorité des observations des sondeurs hyperspectraux, et particulièrement dans les zones atmosphériques sensibles. La méthode d'assimilation des radiances nuageuses développée ici utilise l'information combinée des schémas de détection du CEPMMT et de caractérisation du CO2-Slicing. Pour être efficace ce schéma d'assimilation nécessite une bonne concordance des performances de détection et de caractérisation des nuages pour les deux algorithmes. La première partie de ce manuscrit a permis de montrer que les deux algorithmes sont capables de détecter de manière fiable les nuages. La bonne concordance des performances obtenues d'un schéma à l'autre justifie par ailleurs leur utilisation conjointe dans une otique d'assimilation des radiances nuageuses. Le schéma d'assimilation développé dans cette étude permet d'augmenter le volume total des observations assimilées de plus de 10% pour AIRS et de plus de 12% pour IASI, les observations supplémentaires étant majoritairement localisées dans les moyennes et hautes latitudes. La prise en compte de l'effet du nuage dans l'opérateur d'observation conduit par ailleurs à une simulation d'observations plus cohérente avec les observations réelles. Les expériences réalisées avec AIRS montrent un impact positif sur les prévisions sans être significatif pour la température,l'humidité et le vent. L'impact est significativement positif pour le géopotentiel. Les expériences préliminaires réalisées pour le sondeur IASI montrent un impact sur les prévisions plus mitigé. La prise en compte des données infrarouges issues des sondeurs hyperspectraux en condition nuageuse améliore la prévisibilité des évènements intenses pour les 2 cas d'étude traités dans ce manuscrit de thèse (tempête méditerranéenne du 26 septembre 2006 et tempête sur la bordure ouest Atlantique du 24 janvier 2009). L'assimilation opérationnelle de ce type de données pourrait ainsi permettre, entre autres, une meilleure gestion des risques et ainsi une prévention des menaces liées à ce type de situations plus efficaceThe main goal of this PhD work is to propose an approach to deal with high-spectral-resolution infrared sounders in cloudy conditions. Untill now, these observations were rejected by the data assimilation system due to the complex nature of clouds and to their non-linear processes evolving into spatiotemporal scales lower than those of the model. The emergence of variational techniques as well as improvements achieved in terms of cloud modelisation and radiative transfer revived the interests of the scientific community for the assimilation of cloudy radiances. Indeed most measurements from high-spectral-resolution infrared sounders, and in particular, in atmospheric sensitive regions, are contaminated by clouds. The approach proposed here to deal with cloudy radiances is based on the combined information from the cloud detection algorithm developped by the ECMWF and the CO2-Slicing cloud characterization algorithm. To be efficient, this scheme thus needs a good correspondance in terms of cloud detection between these two algorithms. The fist part of this study demonstrates that these two algorithms are able to detect clouds efficiently. The good correspondance in performances obtained from both algorithms justify their conjoint use to assimilate cloudy radiances. The assimilation scheme developped in this PhD work enables to increase the total amount of assimilated observations by more than 10% for AIRS and by more than 12% for IASI, additional observations are mainly located at mid to high latitudes. In addition, taking into account the cloud effect into the observation operator leads to model equivalents more consistent with true observations. Experiments performed with the AIRS sounder exhibit a positive but not significant impact on forecasts for the temperature, the humidity and the wind. The impact is significantly positive for the geopotential. Preliminary experiments performed with the IASI sounder exhibit a rather mitigated impact. Taking into account cloudy radiances from high-spectral-resolution infrared sounders improves the predictability of intense event for both study cases treated in this work (a mediterrean storm occuring on the 26th of september 2006 and an atlantic storm on the 24th of january 2009). The operational assimilation of this kind of data will certainly enable, among others, a better risk management et thus a more efficient hazard prevention
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Boucher, Eulalie. "Designing Deep-Learning models for surface and atmospheric retrievals from the IASI infrared sounder." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS145.
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L'observation de la Terre est essentielle pour comprendre et surveiller le comportement complexe de notre planète. Les satellites, équipés d'un certain nombre de capteurs sophistiqués, constituent une plateforme clé à cet égard, offrant une opportunité d'observer la Terre à l'échelle globale et de manière continue. Les techniques d'apprentissage automatique (ML) sont utilisées depuis plusieurs décennies, dans la communauté de la télédétection, pour traiter la grande quantité de données générées quotidiennement par les systèmes d'observation de la Terre. La révolution apportée par les nouvelles techniques de Deep Learning (DL) a toutefois ouvert de nouvelles possibilités pour l'exploitation des observations satellitaires. Cette thèse vise à montrer que des techniques de traitement d'images telles que les réseaux neuronaux convolutifs (CNN), à condition qu'elles soient bien maîtrisées, ont le potentiel d'améliorer l'estimation des paramètres atmosphériques et de surface de la Terre. En considérant les observations à l'échelle de l'image plutôt qu'à l'échelle du pixel, les dépendances spatiales peuvent être prises en compte. De telles techniques sont utilisées dans cette thèse pour l'estimation des températures de surface et atmosphériques, ainsi que pour la détection et la classification des nuages à partir des observations de l'Interféromètre Atmosphérique de Sondage dans l'Infrarouge (IASI). IASI, qui est placé à bord des satellites en orbite polaire Metop, est un sondeur hyperspectral collectant des données sur une large gamme de longueurs d'onde dans l'infrarouge. Chacune est adaptée à l'identification des constituants atmosphériques à différents niveaux de l'atmosphère, ou de paramètres de surface. En plus d'améliorer la qualité des restitutions, de telles méthodes d'Intelligence Artificielle (IA) sont capables de traiter des images contenant des données manquantes, de mieux estimer les événements extrêmes (souvent négligés par les techniques statistiques traditionnelles) et d'estimer les incertitudes des restitutions. Cette thèse montre pourquoi les méthodes d'IA, et en particulier les CNN avec convolutions partielles, devraient constituer l'approche privilégiée pour l'exploitation des observations provenant de nouvelles missions satellitaires telles que IASI-NG ou MTG-S IRSObserving the Earth is vital to comprehend and monitor the complex behaviour of our planet. Satellites, equipped with a number of sophisticated sensors, serve as a key platform for this, offering an opportunity to observe the Earth globally and continuously. Machine Learning (ML) techniques have been used in the remote sensing community for several decades to deal with the vast amount of data generated daily by Earth observation systems. The revolution brought about by novel Deep Learning (DL) techniques has however opened up new possibilities for the exploitation of satellite observations. This research aims to show that image-processing techniques such as Convolutional Neural Networks (CNNs), provided that they are well mastered, have the potential to improve the estimation of the Earth's atmospheric and surface parameters. By looking at the observations at the image scale rather than at the pixel scale, spatial dependencies can be taken into account. Such techniques will be used for the retrieval of surface and atmospheric temperatures, as well as cloud detection and classification from the Infrared Atmospheric Sounding Interferometer (IASI) observations. IASI, onboard the polar orbiting satellites Metop, is a hyperspectral sounder gathering data across a broad range of infrared wavelengths that are suitable to identify atmospheric constituents for a range of atmospheric vertical levels, as well as surface parameters. In addition to improving the quality of the retrievals, such Artificial Intelligence (AI) methods are capable of dealing with images that contain missing data, better estimating extreme events (often overlooked by traditional ML techniques) and estimating retrieval uncertainties. This thesis shows why AI methods should be the preferred approach for the exploitation of observations coming from new satellite missions such as IASI-NG or MTG-S IRS
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Tournadre, Benoît. "Heliosat-V ˸ une méthode polyvalente d’estimation du rayonnement solaire au sol par satellite." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLM063.
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L'éclairement du Soleil à la surface de la Terre est reconnu comme une variable climatique essentielle par l'Organisation Météorologique Mondiale. Sa connaissance est aussi précieuse pour les sciences du climat que pour le développement d'énergies alternatives aux combustibles fossiles, comme le solaire photovoltaïque. La mesure au sol de ce rayonnement est très clairsemée sur la Terre, d'où l'intérêt de méthodes d'estimation basées sur la télédétection par satellite. Combiner les estimations produites à partir de différents satellites en orbite est une voie pour couvrir au mieux l'information sur tout le globe terrestre. De plus, différentes générations de satellites ont produit une imagerie de la Terre depuis plusieurs décennies, permettant d'estimer de longues séries temporelles du rayonnement solaire, voire d'identifier des variations long terme, un objectif récurrent dans l'étude du changement climatique. Depuis plus de trente ans, les méthodes Heliosat permettent cette estimation, mais elles ont été conçues pour être appliquées à un capteur spécifique en orbite géostationnaire et ont des contraintes limitant leurs champs d'application : la nécessité d'utiliser une longue série temporelle passée (Heliosat, Heliosat-2), ou le besoin de mesures multispectrales (Heliosat-4). Ce travail sur le développement d'une méthode Heliosat-V apporte des éléments de polyvalence à l'estimation satellite par les méthodes dites à "indice d'ennuagement", dans l'objectif de tendre vers une donnée homogène du rayonnement solaire issue de mesures de différents instruments satellites. Deux problèmes sont en particulier considérés pour parvenir à cette estimation : la diversité des capteurs en termes de sensibilités spectrales, et l'influence des géométries de visée et d'éclairement solaire sur les mesures satellites. La méthode s'appuie extensivement sur la modélisation du transfert radiatif dans l'atmosphère dans la gamme spectrale 400-1000 nm pour simuler d'une part les mesures de radiomètres satellites en conditions de ciel clair et d'autre part celles en présence d'un nuage optiquement épais. La méthode est testée sur l'imagerie d'un instrument satellite géostationnaire, Meteosat-9/SEVIRI, et de manière plus exploratoire sur celle d'un non géostationnaire, DSCOVR/EPIC. Les résultats sont comparés à des mesures de référence au sol de l'éclairement, et montrent des performances similaires à celles de produits opérationnels d'éclairement solaire. La qualité des estimations dépend cependant du canal spectral utilisé, en particulier de la présence de diffusion ou d'absorption de l'atmosphère claire dans le signal mesuré par satellite. L'accent est aussi mis sur le besoin d'un étalonnage absolu précis des mesures radiométriques satellites pour produire des séries temporelles d'éclairement de surface avec des biais et une dérive temporelle les plus faibles possiblesSolar irradiance at the surface of the Earth is recognized as an essential climate variable by the World Meteorological Organization. Its knowledge is as much important for climate sciences as for the development of energy alternatives to fossil fuels, like solar photovoltaic. Ground measurements of this radiation are very sparse on Earth, explaining the interest for satellite-based remote sensing to estimate it. Combining estimations from different satellites in orbit is a pathway to cover the information on the whole globe. Different generations of satellites also produced a multidecadal imagery of the Earth, making it conceivable to estimate long time series of solar radiation, or even to identify long-term variations, a recurrent objective in the study of climate change. For more than 30 years, Heliosat methods estimate surface solar irradiance from satellite imagery, but they have been designed to be applied to a specific sensor on a geostationary orbit, and have limitations in their scope : the need for a long archive of satellite imagery (Heliosat, Heliosat-2), or else the need for multispectral measurements (Heliosat-4). This work dedicated to the development of a Heliosat-V method brings elements of versatility to the satellite-based estimation from so-called "cloud-index" methods, with the ultimate goal to reach homogeneous data of solar radiation derived from measurements made by different satellite instruments. Two issues are in particular considered here to reach such an estimation: the diversity of sensors in terms of spectral sensitivities, and the influence of viewing and solar geometries on spaceborne measurements. The method extensively deals with radiative transfer modeling in the spectral range 400-1000 nm to simulate on one hand satellite measurements in clear-sky conditions, and on the other hand satellite measurements in the presence of an optically thick cloud. The method is tested on the imagery of a geostationary satellite instrument, Meteosat-9/SEVIRI, and in a more exploratory way, on the non geostationary sensor DSCOVR/EPIC. Results are compared to high quality ground-based measurements of irradiance, and show performances similar to operational satellite products. However, the quality of estimates depends on the spectral channel used, and especially of the presence of clear-sky atmospheric scattering or absorption in the signal measured by the satellite instrument. The accent is also put on the need for an accurate absolute calibration of satellite radiometric measurements in order to produce time series of surface solar irradiance with the smallest biases and temporal drift possible
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Ruffenach, Alexis. "Observation et modélisation de l'érosion des nuages magnétiques solaires par reconnexion magnétique." Phd thesis, Université Paul Sabatier - Toulouse III, 2013. http://tel.archives-ouvertes.fr/tel-00953668.
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Les nuages magnétiques ("Magnetic Clouds ", MCs) sont assimilés à des structures helicoïdales à grande échelle interagissant avec le milieu interplanétaire au cours de leur propagation. McComas et al. (1988), suivi par Dasso et al. (2006), ont envisagé la reconnexion magnétique comme processus pouvant graduellement éroder la structure externe des éjections de masse coronale interplanétaires. Ce processus d'érosion est le sujet central de cette thèse. Tout d'abord, nous confirmons l'existence de l'érosion d'un nuage magnétique grâce à une étude multi-satellites combinant un ensemble de signatures clés. Après avoir déterminé l'orientation des axes du MC par différentes méthodes, nous estimons le taux de flux magnétique érodé en analysant les variations du flux magnétique azimutal du MC. Nous démontrons aussi la présence de signatures de reconnexion magnétique à la frontière avant du MC, tel qu'attendue. Finalement, nous étudions les caractéristiques de la distribution en angle d'attaque des électrons suprathermiques dans la région arrière du MC. Ces électrons indiquent des modifications topologiques à grande échelle, attendues du processus d'érosion. Dans une seconde partie, une analyse statistique de tous les nuages magnétiques observés au cours de la période 1995-2008 est réalisée dans le but de quantifier ce processus. Nous montrons que ce processus est récurrent : l'érosion est relevée à l'avant et à l'arrière dans les mêmes proportions. Cela est confirmé par l'étude statistique des jets de plasma aux frontières, qui démontre indépendamment la fréquence élevée du processus d'érosion. Dans une dernière partie, parce que le mécanisme d'érosion est susceptible de supprimer une partie de flux magnétique orienté vers le Sud d'un MC, à l'avant ou à l'arrière, nous étudions l'impact potentiel de l'érosion sur la géo-efficacité résultante, en utilisant un modèle de MC combiné à un modèle empirique de l'intensité du courant annulaire terrestre. Nous modélisons aussi l'évolution radiale de ce processus. Nous concluons que la majeure partie de l'érosion se produit à l'intérieur de l'orbite de Mercure.
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Eisenbeis, Julian. "Ionospheric Dynamics by GNSS total electron content observations : the effect of Solar Eclipses and the mystery of Earthquake precursors." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7027.
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Cette thèse porte principalement sur deux sujets: l'un est la signature ionosphérique des éclipses solaires, l'autre est le débat ‘Hole vs Enhancement’. Le 21 août 2017, l'ombre d'une éclipse totale a changé radicalement l'état de l'ionosphère au-dessus des Etats-Unis. Cet effet est visible dans le contenu total en électrons (TEC) mesuré par ~3000 stations GNSS qui voient des multiples satellites GPS et GLONASS. Ce formidable ensemble de données permet une caractérisation à haute résolution du contenu en fréquences et des longueurs d'onde - en utilisant une analyse omega-k basée sur la Transformée de Fourier Rapide (FFT) 3D - de la signature de l'éclipse dans l'ionosphère afin d'identifier complètement les perturbations ionosphériques mobiles (TID). Nous confirmons la génération de TIDs associées à l'éclipse, y compris les TIDs interprétées comme des ondes de proue dans les études précédentes. De plus, nous révélons, pour la première fois, des TID de courte (50-100 km) et de longue (500-600 km) longueurs d'onde avec des périodes entre 30 et 65 min (Eisenbeis et al., 2019). Le 2 juillet 2019, une autre éclipse solaire totale s'est produite à travers le continent sud-américain. Bien que nous n'ayons que des données provenant de plus de cent stations GNSS et situées dans une zone proche du coucher du soleil, nous pouvons montrer la preuve évidente de la signature ionosphérique de l'éclipse (Eisenbeis & Occhipinti in prep.a). Le deuxième grand sujet de ce travail est le débat sur la possibilité de précurseurs de séismes. Heki (2011) a suscité ce débat en publiant les résultats du séisme de Tohoku montrant une amélioration de la TEC avant le séisme. L'amélioration revendiquée par Heki (2011) a été interprétée comme une diminution de la TEC après l'événement, le soi-disant trou ionosphérique dans la littérature. L'existence de l'amélioration a été promue par plusieurs articles (e.g. He & Heki, 2017) étendant l'observation à plusieurs événements de magnitude modérée (M> 7.5) et propose une nouvelle vision de la dynamique de rupture. En essayant de reproduire leurs résultats, nous montrons que la courbe de référence utilisée par Heki (2011) est affectée par l'ordre d'ajustement polynomial ainsi que par les fenêtres temporelles sélectionnées. Ceci montre que l'amélioration du TEC pourrait en fait n'être qu'un artefact, subjectivement sélectionné pour créer le précurseur présumé (Eisenbeis & Occhipinti in prep.b)This thesis focuses mainly on two topics: one is the ionospheric signature of solar eclipses, the second is the Hole vs Enhancement debate about earthquake precursors. On the 21st August 2017 the shadow of a total eclipse drastically changed the state of the ionosphere over the USA. This effect is visible in the total electron content (TEC) measured by ~3000 GNSS stations seeing multiple GPS and GLONASS satellites. This tremendous dataset allows high-resolution characterization of the frequency content and wavelengths -using an omega-k analysis based on 3D Fast-Fourier-Transform (FFT)- of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances (TIDs). We confirm the generation of TIDs associated with the eclipse including TIDs interpreted as bow waves in previous studies. Additionally we reveal, for the first time, short (50-100 km) and long (500-600 km) wavelength TIDs with periods between 30 and 65 min (Eisenbeis et al., 2019). On 2nd July 2019 another total solar eclipse happened across the South American continent at magnetic conjugate latitudes as the Great American Eclipse, and consequently useful to visualize the difference response. Although for the South American eclipse we have only data from more than hundred GNSS stations and located in a zone close to the sunset, we can show the clear evidence of the ionospheric signature of the eclipse (Eisenbeis & Occhipinti in prep.a).The second major topic in this work is the still ongoing debate about the possibility of earthquake precursors. Heki (2011) sparked this debate when he published results of the Tohoku earthquake showing a TEC enhancement before the earthquake. The enhancement claimed by Heki (2011) has been interpreted as a decrease in the background TEC after the seismic event, the so called ionospheric hole in literature. The existence of the enhancement has been promoted by several papers (e.g. He & Heki, 2017) extending the observation to several events with moderate magnitude (M> 7.5) and proposes a new vision of the rupture dynamics. By trying to reproduce their results we show that the reference curve used by Heki (2011) to define the TEC background is strongly affected by the order of polynomial fit as well as the selected time windows. This shows that the TEC enhancement could be, in fact, just an artifact, subjectively selected to create the presumed precursor (Eisenbeis & Occhipinti in prep.b)
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Kurzrock, Frederik. "Assimilation de données satellitaires géostationnaires dans des modèles atmosphériques à aire limitée pour la prévision du rayonnement solaire en région tropicale." Thesis, La Réunion, 2019. https://elgebar.univ-reunion.fr/login?url=http://thesesenligne.univ.run/19_13_FKurzrock.pdf.
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La variabilité de l’énergie solaire impose de limiter sa fraction d’injection instantanée dans le réseau électrique. Une amélioration des prévisions de l’ensoleillement conduirait à élever la limite de ce seuil, spécialement dans les zones non-interconnectées comme La Réunion. Une plus haute précision de prévision est particulièrement difficile à atteindre dans le cas des îles tropicales à cause de la convection prononcée et des circulations thermiques complexes au niveau local. Les modèles de prévision numérique du temps à aire limitée permettent de prévoir les processus liés aux nuages et l'éclairement solaire à de hautes résolutions spatio-temporelles, de l’ordre de quelques kilomètres et minutes. Néanmoins, ces modèles parviennent rarement à prévoir précisément l'évolution de la couche nuageuse et ont donc tendance à surestimer l'éclairement solaire. L’affinement des conditions initiales nuageuses des modèles régionaux par l’assimilation d’observations de satellites météorologiques géostationnaires est un moyen efficace pour améliorer les prévisions à court terme. Toutefois, une grande variété d'approches pour l'assimilation des données satellitaires existe et, jusqu'à présent, la recherche s’est concentrée sur les moyennes latitudes. Cette thèse aborde l'assimilation d'observations de satellites géostationnaires avec des modèles à aire limitée dans le sud-ouest de l'Océan Indien. Dans un premier temps, l'état de l'art des approches existantes pour l'assimilation de luminances observées et de propriétés physiques des nuageuse avec les modèles régionaux est dressé. Puis, l'une des approches les plus prometteuses est identifiée et appliquée au sud-ouest de l'Océan Indien. Dans les expériences effectuées, la teneur en eau des nuages est obtenue à partir des produits de propriétés nuageuses SatCORPS de la NASA. Ces observations sont assimilées avec un filtre de Kalman d’ensemble et le modèle Weather Research and Forecasting. Un ensemble de 41 membres et un espacement horizontal des points de grille de 12 km est appliqué avec un intervalle de cyclage de 6 heures pour l'assimilation. Le Data Assimilation Research Testbed et son opérateur d'observations de teneur en eau des nuages sont utilisés pour l'assimilation d'observations dans les phases solide, surfondue, et liquide. L'impact de cette approche d'assimilation sur des prévisions de l'éclairement horizontal global est évalué pour l'été austral 2017/2018 en utilisant des observations de pyranomètres sur l'île de La Réunion. Un effet positif de la méthode appliquée sur les prévisions de l'éclairement est constaté surtout pour les 14 premières heures de prévision. Différents aspects de l'amélioration des prévisions, grâce à l'assimilation de données, sont analysés par le biais d’expériences témoins sans assimilation, d’expériences avec un domaine de grille imbriquée avec un espacement horizontal des points de grille de 4 km et d’une comparaison avec des modèles opérationnels. Les observations quadrillées utilisées étant disponibles à l'échelle mondiale, la méthode offre une approche applicable et évaluable pour d'autres régions du mondeThe variability of solar irradiance necessitates to limit the instantaneous feed-in of solar power to electricity grids. An improvement of solar irradiance forecasts would allow to increase the defined threshold limits, especially in non-interconnected zones such as Reunion Island. Achieving higher forecast accuracy is particularly challenging in the case of tropical islands due to pronounced convection and local thermal circulations. Limited-area numerical weather prediction (NWP) models allow to forecast cloud processes and solar irradiance at high spatio-temporal resolutions of a few kilometres and minutes. Nevertheless, they often fail to accurately predict cloudiness evolution and thus tend to overestimate solar irradiance. Refining the initial conditions of regional models in terms of clouds is an efficient means for improving short-term cloud cover and irradiance forecasts. The assimilation of geostationary meteorological satellite observations can achieve this improvement. Nevertheless, a variety of satellite data assimilation (DA) approaches exist and research has focused on mid-latitudes so far. This thesis deals with the assimilation of geostationary satellite observations with limited-area models in the southwestern Indian Ocean. In a first step, the state of the art in terms of existing approaches for radiance and cloud property retrieval assimilation with regional-scale models is reviewed. In consequence, one of the most promising approaches is identified and applied to the southwestern Indian Ocean. In the performed experiments, multi-phase cloud water path retrievals from NASA Langley's SatCORPS cloud products are assimilated with an ensemble Kalman filter using the Weather Research and Forecasting model. A 41-member ensemble at 12 km grid spacing is applied with a DA cycling interval of 6 hours. The Data Assimilation Research Testbed and its forward operator for cloud water path are used to assimilate gridded cloud water retrievals in the ice, supercooled liquid, and liquid phase. The impact of this assimilation approach on forecasts of global horizontal irradiance (GHI) is evaluated for austral summer 2017/2018 using pyranometer observations on Reunion Island. A distinct positive impact of the applied method on the first 14 hours of GHI forecasts is found. Different aspects of the forecast improvement due to DA are analysed by means of control experiments without DA, experiments with a nested domain at 4 km grid spacing, and a comparison with operational NWP models. As the utilised gridded cloud products are available globally, the method offers a portable and globally applicable approach that may also be evaluated for other regions of the Earth
Books on the topic "Observations par sodar"
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Dunlop, Storm. 9. Worldwide effects and forecasting. Oxford University Press, 2017. http://dx.doi.org/10.1093/actrade/9780199571314.003.0009.
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Observing the weather for purposes of forecasting is a worldwide enterprise. Routine measurements are made by national agencies in every country of the globe. These observations and their distribution are handled by international agreement and the World Meteorological Organization, a specialized agency of the United Nations. It has become obvious that events in one part of the world may have a great effect on weather experienced in distant regions. ‘Worldwide effects and forecasting’ considers these long-distance relationships between various atmospheric conditions—teleconnections—the most famous being El Niño. It also looks at the potential solar influence on Earth’s weather, as well as how chaos theory is used in ensemble forecasting.
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Balyshev, Marat. Astronomical research in Kharkiv at the end of the 19th century – the first half of the 20th century. “Naukova Dumka”, 2022. http://dx.doi.org/10.15407/978-966-00-1863-1.
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The main milestones of the formation and development of astronomical science in Kharkiv during 1883–1945 are reconstructed on the example of the activities of the astronomical observatory of Kharkiv University. During this period, the outstanding worldview science in Kharkiv has achieved significant success: the works of Kharkiv astronomers have received world recognition; a well-known scientific planetary school has been established at the Observatory; the scientific community highly appreciated the research on the physics and chemistry of the Moon, the giant and small planets of the Solar System. The primary goal of the research is to inscribe the history of the university Observatory into the European and world context. Its purpose is to summarize the results of a comprehensive historical ad scientific study of the development of astronomical research in Kharkiv at the end of the 19th century – the first half of the 20th century and identification of ways of further scientific research. The completed research, which continues the problems of works devoted to the study of the history of astronomical science in Ukraine, focuses on expanding the well-known source base by attracting new retro-information resources. In particular, the monograph used a significant array of archival primary sources from almost twenty archival and library institutions of different countries. Most of them were introduced into scientific circulation for the first time, which allowed to determine and specify the sequence of stages of development of astronomical science in Kharkiv during the research period, to clarify and identify the little-known circumstances of the observatory life. The methodological basis of the study is the principles of historism, objectivity and a systematic approach to studying the problem. To solve specific problematic tasks in the monograph, general scientific and specially historical methods were used which allowed to study, analyze and summarize the presented factual material in a complex manner. The main sections of the monograph represent the dynamics of replenishment of the instrumental base of the university observatory, the chronology of the construction of the observatory complex of buildings at the location of the modern Scientific Research Institute of Astronomy of the V. N. Karazin Kharkiv National University. According to the author’s periodization, the stages of formation of subjects and directions of scientific work of university astronomers have been analyzed, including: seismic observations with the help of horizontal Rebeur-Paschwitz pendulums, research of the activity of the Sun, astrometric observations on the Repsold meridian circle of for the purpose of compiling a catalog of zodiac stars, studying lunar eclipses and meteor showers. The participation of university astronomers in the creation of the plan of the city of Kharkiv and its connection with the general network of precise geometric leveling of the Military Topographic Department of the General Staff; the organization of observations by an expedition of Kharkiv astronomers of the total Solar eclipse of 1914 in Henichesk; the creation of the School-workshop of precision mechanics at the Faculty of Physics and Mathematics of Kharkiv University were considered; information on the participation of Kharkiv astronomers in the events of the civil war during the Ukrainian Revolution was documented. The scientific research activity of Kharkiv astronomers during 1920-1930-s which was devoted to carrying out important astrometric works on meridian observations of star declinations by absolute methods and observations of Kopf-Rentz stars according to the programs of the International Astronomical Union; the initiation of the creation of the Catalog of faint stars; research in astrophysics aimed at studying the physical conditions on the Moon and the Sun, planets and the interstellar environment; performing long series of spectrophotometric observations of the Moon, Jupiter, Mars and Saturn under different conditions of observation; study of the kinematics of stellar systems of different order, the physical parameters and evolution of stars, the morphology of the Galaxy, the nature of the stellar subsurfaces and atmospheres, dust and gas nebulae, new stars and the variability of stars have been considered; the directions of solid works carried out in the field of celestial mechanics, devoted to the dynamics of the minor planets of the Jupiter group, the definition and improvement of the orbits of minor planets have been clarified. The development of amateur astronomy in Kharkiv, in particular, the functioning of circles and societies that directed their activities to the dissemination of astronomical knowledge, was highlighted; the participation of their representatives in astronomical observations at the Kharkiv Astronomical Observatory was emphasized. Reconstructed the development of historical events in the 1930s related to the involvement of Soviet and Western astronomers in the processes of political confrontation between the USSR and the Western world; investigated the course of circumstances that prevented the implementation of the project of creating a new modern astronomical center of national importance – the central Ukrainian observatory in Kharkiv; the participation of an expedition of Kharkiv astronomers in the observation of the «great Soviet eclipse» – the total solar eclipse of 1936 – in the North Caucasus is highlighted; established the facts of political «purges» and repressions by the People’s Commissariat for Internal Affairs ( the NKVD) in the Kharkiv Astronomical Observatory. The activity of the Kharkiv Astronomical Observatory has been documented and authentic biographical information about its representatives during the Nazi occupation of 1941–1943, the period of the German-Soviet war, has been presented; the unpopular facts of the forced collaboration of some scientists are highlighted; the process of recovery and reconstruction of the Kharkiv Astronomical Observatory after the liberation of the city is characterized. With the aim of researching the personal history of Kharkiv astronomy of the studied period, the monograph presents the results of a historical and biographical study of facts of life and scientific heritage of scientists who fully devoted themselves to Science, laid the foundations for the future development of many directions of modern astronomical research, made a significant contribution to the treasury of the national and European astronomical science, whose activities were connected with the Kharkiv Astronomical Observatory, in particular: Grigory Levytsky, Ludwig Struve, Mykola Evdokymov, Otto Struve, Mykola Barabashov, Boris Gerasimovich, Vasil Fesenkov, Oleksiy Razdolsky, Boris Ostashchenko-Kudryavtsev, Nicholas Bobrovnikov, Paraskovia Parkhomenko, Mstislav Savron, Boris Semeykin, Kostyantyn Savchenko and others (25 biographical essays are presented). A significant part of the mentioned factual material was also introduced into scientific circulation for the first time. A separate section of the monograph provides chronologically structured information that reflects the sequence of research work of the Kharkiv Astronomical Observatory employees during the period under study: from astrometric observations of stars and seismic research to spectrohelioscopic and spectroheliographic observations of the Sun and the initiation of the Kharkiv school of planetary science. It is assumed that the materials of the monograph will be used in research work devoted to the study of the process of institutionalization of astronomical research in Kharkiv at the end of the 19th century – the first half of the 20th century.
Book chapters on the topic "Observations par sodar"
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Goss, W. M., Claire Hooker, and Ronald D. Ekers. "The Sun and the Ionosphere, 1946–1955." In Historical & Cultural Astronomy, 381–91. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-07916-0_25.
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AbstractWhen David Martyn wrote to Pawsey in August 1952 to propose his nomination for the Royal Society, Pawsey replied with a formal typed letter that included an obligatory modest paragraph, followed by his own assessment of his achievements. In his own assessment, his main scientific contributions were in solar radio astronomy (which in 1952, he considered the “most fruitful” investigations at RPL, rather than the new found interest in the discrete sources and extra-Galactic observations) and the development of new methods of ionospheric research. We therefore devote this chapter to a brief summary of research and achievements in these areas up to 1955. The first part of the chapter contains a brief overview of the main achievements in solar radio astronomy, led by Paul Wild. Often it is difficult to identify Pawsey’s particular contributions, because, as noted, his leadership style was to visit and discuss observations and analyses, to make comments and propose ways of resolving immediate difficulties, but not to lead the research nor to take authorship for such contributions, However many papers do acknowledge Pawsey’s advice and criticisms in their preparation. The second part contains an overview of Pawsey’s well-crafted but not extensive ionospheric research.
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Altschuler, Daniel R., and Fernando J. Ballesteros. "Understanding the Moon." In The Women of the Moon, 5–34. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198844419.003.0002.
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This chapter provides background material to put the Moon in context and to understand how craters came to be formed, as part of the formation of the solar system. It presents a brief history of the solar system and the first observations of the Moon, and how they affected its portrayal in art and literature. The measurement of its distance and the misunderstood “dark side” are also described.
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Chambers, John, and Jacqueline Mitton. "Worlds of Gas and Ice." In From Dust to Life. Princeton University Press, 2017. http://dx.doi.org/10.23943/princeton/9780691175706.003.0012.
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This chapter focuses on the giants of the solar system. Astronomers know somewhat less about the giant planets—except Jupiter—since no probes have gone down through their atmospheres and examined them directly. However, remote observations show that they have much in common with Jupiter. The low densities of all four giants mean they are mostly made of much lighter stuff than their terrestrial cousins. As on Jupiter, most of this bulk is gaseous in the outer layers but must be compressed into liquids in the interior. None of the giants has a solid surface, and the transition between gas and liquid is not a sharp one. Astronomers refer to the outer part of the fluid envelope as the atmosphere, although the depth of the base of the atmosphere is rather arbitrary.
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Easton, Robert W. "Examples." In Geometric Methods for Discrete Dynamical Systems, 3–17. Oxford University PressNew York, NY, 1998. http://dx.doi.org/10.1093/oso/9780195085457.003.0001.
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Abstract A mathematical model of a physical system consists of a set which represents all “states” of the system together with a law which determines the time evolution of states. Part of a scientist’s job is to identify the relevant set of states and to propose the law which governs their evolution. For example, states for Newton’s model of the solar system consist of all positions and velocities of the sun and planets. The law of evolution is determined by a system of second-order differential equations. Newton’s model does not include effects due to the spins, oblateness, magnetic fields of the sun and planets, or the effect of the solar wind. With most models, not every effect is taken into account, just the essential effects. Success of a model is judged by comparing its predictions with observations. Study of a successful model often provides new insight into the physical system being studied and it may suggest new experiments. For Newton’s model of the solar system, the differential equations governing the motion cannot be solved in terms of elementary functions. Attempts to solve these equations approximately using computers are successful over time periods of thousands of years, but they are not accurate over millions or hundreds of millions of years. Round-off errors and truncation errors due to the numerical method tend to grow over time and these eventually limit accuracy. Furthermore, deterministic chaos or instability in the dynamics may cause errors to grow exponentially in time. Attempts to model the solar system illustrate that even when the physical laws governing the evolution of a system are exactly known, and the initial state of the system is exactly known, there may be no practical way of predicting the state far in the future. This presents a new challenge to the modern scientific method which is just beginning to be appreciated and addressed.
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He, Fei, Zhonghua Yao, and Yong Wei. "Optical Remote Sensing of Planetary Space Environment." In Remote Sensing [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.98427.
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Planetary science is the scientific investigations of the basic characteristics and the formation and evolution processes of the planets, moons, comets, asteroids and other minor bodies of the solar system, the exoplanets, and the planetary systems. Planetary scientific research mainly depends on deep space exploration, and it is highly interdisplinary and is built from Earth science, space science, astronomy and other relevant disciplines. Planetary space, a critical region of mass and energy exchange between the planet and the interplanetary space, is an integral part of the planetary multi-layer coupling system. Atmospheres of different compositions and plasmas of different densities and energies exist in planetary space, where mass transportation at different temporal and spatial scales and various energy deposition and dissipation processes occur. Optical remote sensing overcomes the difficulties of capturing global views and distinguishing spatiotemporal variations in in-situ particle and field detections. This chapter introduces the principles and applications of optical remote sensing in planetary science. The first ground-based planetary observatory in China, the Lenghu Observation Center for Planetary Sciences, will be introduced in detail. Future development of optical remote sensing platforms in Chinese planetary exploration program will also be introduced.
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Bertuglia, Cristoforo Sergio, and Franco Vaio. "Modelling." In Nonlinearity, Chaos, and Complexity, 10–18. Oxford University PressOxford, 2005. http://dx.doi.org/10.1093/oso/9780198567905.003.0002.
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Abstract During our entire lives we learn to construct mental models of the world that surrounds us. Catching a falling object by anticipating where it is going to fall before it gets there, understanding the thoughts of an interlocutor before he speaks on the basis of a few signs, deciphering the intentions of an opponent before he acts; these are just a few examples of how we read a situation and its various aspects, something that we all do constantly, constructing models based on our store of previous experiences as well as our attempts or mistakes. As we said in Chapter 1, in science, the study of systems that evolve over time, i.e. of systems whose state changes over time, is particularly interesting. The swinging of a pendulum, the radioactive decay of a substance, the movement of the planets in the solar system, the growth of a plant, the trend in the number of individuals of a particular population in a defined territory, the flow of road traffic along a street or that of telephone communications in a channel and the trend of a stock exchange index, are just some examples of what we mean by a system that evolves over time. In each of the above examples, as in many others, we have a set of states at various points in time and we seek a law of motion that reproduces the succession of these states over time. A large part of scientific work, from the very origins of science onwards, has concentrated on establishing the ‘right’ law of motion to describe the evolution of a system over time, based on observations of a limited set of successive states (Casti, 2000). When these activities lead to the formulation of recurrences (laws) in a mathematical language, then we have a mathematical model.
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Kattawar, George W. "Polarization of Light in the Ocean." In Ocean Optics. Oxford University Press, 1994. http://dx.doi.org/10.1093/oso/9780195068436.003.0015.
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The effects of polarization on our perception of the environment about us have been recognized for at least 1000 years. The earliest reports were in response to the polarization in blue skylight as observed through various polarizing crystals. Since blue skylight is a source of polarized light, and atmospheric observations are a quite natural part of our daily routine, it is not surprising that an extraordinary amount of research on the polarization of skylight has been undertaken. Study of the polarization properties of the ocean and the hydrosols contained therein has, unfortunately been very limited, perhaps because man has not been a natural resident of the sea. This chapter will introduce a description of the polarized light field beneath the sea by first providing a brief history of polarization. This will familiarize the reader with its rather ubiquitous presence in our environment, even though our visual perception of it is very weak. Finally, a method is presented (Mueller matrices) to fully characterize the polarization properties of the submarine light field and the polarized effects that various hydrosols have on the light field. For a collection of the many diverse applications of polarization, the reader is referred to the excellent book by Gehrels (1974) About 1000 years ago, the Vikings discovered the dichroic properties of crystals such as cordierite. This property of exhibiting various colors when viewed from different directions is due to the selective absorption of waves oscillating along a particular plane of the crystal. When Vikings viewed the blue skylight through such crystals held in a certain orientation, they located portions of the sky relative to the solar position that seemed to disappear. With this discovery of the polarization of the blue sky, they learned to navigate even in the absence of the sun (e.g., when it was below the horizon). It was another six and one-half centuries before other polarization properties were reported (see Table 11-1 taken from Gehrels, 1974, and Können, 1985).
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Wylie, Donald P. "Cirrus and Weather: A Satellite Perspective." In Cirrus. Oxford University Press, 2002. http://dx.doi.org/10.1093/oso/9780195130720.003.0010.
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Cirrus were originally thought of as benign cloud forms that could be used for predicting the onset of foul weather, such as “mare's tails” and “anvil edges,” but not of great concern because they do not produce any damaging winds or hydrometers. Our original view of cirrus was from the ground, so they were mostly ignored until aircraft started flying in them and making cirruslike contrails in the latter part of World War II. Cirrus limited visibility for the aircraft, and contrails made detection of aircraft from the ground easier. This led to the first studies of cirrus by the Air Force (Stone 1957). Had our first views of earth been from space, cirrus would have been an obvious cloud and often an obstruction to viewing everything else on the planet. Cirrus are difficult to see on visual satellite images, which is deceiving because they reflect enough solar radiation to obscure quantitative measurements of the land and water surfaces. Cirrus are more obvious in window channel infrared images, and they block any sensor that tries to look horizontally through them from either aircraft or satellites. The term “invisible cirrus” originated from an attempt to fly a horizontal viewing sensor on an aircraft for detecting approaching objects (missiles). The sensor was obscured because of its long path length through cirrus, while ground observers did not report the cirrus. Pilots were uncertain whether they were in a cloud or not. The frequency of cirrus reported from satellite data often surprises other scientists. Wylie and Menzel (1999) reported finding cirrus in 25-30% of GOES/VAS (Geostationary Operational Environmental Satellite/Visual spin scan radiometer Atmospheric Sounder) data over the continental United States. A similar satellite instrument flying globally, the HIRS (High Resolution Infrared Radiometer Sounder) on the National Oceanic and Atmospheric Administration (NOAA) satellites, reported cirrus 43% of the time (Wylie and Menzel 1994; Wylie and Menzel 1999). The horizontally viewing SAGE (Stratospheric Aerosol and Gas Experiment) is even more sensitive and reports cirrus in 50-70% of its data (Wang et al. 1996). These numbers should not have surprised people because the compilations of ground-based weather observations by Warren et al. (1988) show cirrus frequencies as high as 75% in Indonesia.
Conference papers on the topic "Observations par sodar"
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Martazinova, Vazira, Vitalii Shpyg, and Yaroslav Kykhtenko. "Analysis of solar radiation changes in large cities of Ukraine in the summer period." In International Conference of Young Scientists on Meteorology, Hydrology and Environmental Monitoring. Ukrainian Hydrometeorological Institute, 2023. http://dx.doi.org/10.15407/icys-mhem.2023.021.
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Solar energy is the cleanest and most common renewable energy source. The solar energy market today is almost 103 gigawatts (GW). According to the International Energy Agency (IEA), about 125 GW of solar energy is produced in the world. In Ukraine, the average annual amount of total energy of solar radiation ranges from 1,070 kWh/m? in the northern part of Ukraine to 1,400 kWh/m? and above in the Autonomous Republic of Crimea. Along with a fairly large number of works devoted to the components of the radiation balance, research is mainly conducted to study their spatio-temporal distribution over the territory, and in Ukraine, the main source of data remains the few weather stations at which relevant observations are made. This exploration uses data from surface observations and reanalysis data. In particular, the surface observation data were taken from the Borys Sreznevsky Central Geophysical Observatory. Reanalysis data - from the European Center for Medium-Range Weather Forecasts, ECMWF [http://www.ecmwf.int/en/research/climate-reanalysis/era-interim]. For the exploration, 5 large cities of Ukraine were chosen, which highlight different parts of the country - Kyiv, Kharkiv, Lviv, Dnipro and Odesa. Validation was carried out on surface observation data using data covering the period 2008-2020. An exploration of the temporal distribution of direct, diffuse and total solar radiation was carried out on reanalysis data covering the period 1991-2020. For each city as a whole, for the summer and for a single month of the season, the values of direct, diffuse and total solar radiation were obtained according to the reanalysis data. The minimum and maximum values that occurred are determined. For each city, a general trend for the summer as a whole and separately for June, July and August was obtained. It was found that the reanalysis tends to underestimate diffuse and overestimate direct solar radiation. According to the reanalysis data, the changes in diffuse solar radiation are insignificant in terms of values for all cities, in terms of the actual direction of changes - for Kyiv, Kharkiv and Lviv, in Dnipro and Odesa at the end of the studied period there is a tendency for it to decrease. In general, these conclusions are confirmed by the data of surface observations, with the exception of Kyiv (for all summer months), as well as for June in Odesa and Lviv, where an increase in its values is observed at the end of the studied period. The largest fluctuations (both according to surface observations and reanalysis) occur for direct solar radiation and, as a result, appear in the amount of total solar radiation. In general, for the summer period in all five cities, there is a tendency to a slight increase in the amount of total solar radiation.
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Hoshizaki, A. James. "Operating Experience of the First Solar® Taurus 70S Mechanical Drive Installation." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-354.
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In October 1995, NOVA Gas Transmission Ltd. (NGTL) commissioned the first mechanical drive application of Solar Turbines’ Taurus™ 70S gas turbine. The unit was installed as a part of a turbine/compressor package at a compressor station on NGTL’s natural gas pipeline system. As this first installation was a part of a development test program by Solar Turbines, field evaluation was conducted subsequent to the original commissioning and related testing. This paper presents NGTL’s experiences in commissioning, startup and operation. Field performance test results for the gas turbine are presented and focus on output power, thermal efficiency and exhaust emissions. Some of the findings and observations from the field evaluation tests performed by Solar are also discussed. In addition, a description of the facility in which the turbine/compressor package is installed is provided.
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McElroy, C. T., J. B. Kerr, D. I. Wardle, L. J. B. McArthur, G. M. Shah, M. Garneau, S. G. MacLean, et al. "SPEAM-I Observations of High-Altitude Ozone from STS 41-G." In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/orsa.1991.pdp3.
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The Sunphotometer Earth Atmosphere Measurement (SPEAM-I) experiment was flown on the United States Space Shuttle Challenger in October, 1984 as part of a group of Canadian experiments referred to as CANEX-I. Measurements of the solar intensity were made through the orbiter side-hatch window at various wavelengths in the visible and near-ultraviolet during a number of terminator crossings using a hand-held, interference filter photometer. Observations at 315 and 324 nm have been analyzed to give vertical profiles of ozone at 63.34°S, 91.96°E. These profiles are compared to data from the literature. The success of this experiment points the way to the use of small instruments to make accurate but inexpensive observations of the composition of the upper atmosphere.
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Ito, A., H. Nakanishi, K. Takayama, I. Kawayama, H. Murakami, and M. Tonouchi. "Observation of THz emissions from various types of solar cells using laser terahertz emission microscope." In 2013 Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR). IEEE, 2013. http://dx.doi.org/10.1109/cleopr.2013.6600523.
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McCormick, M. P. "SAGE III." In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/orsa.1990.mb8.
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The Stratospheric Aerosol and Gas Experiment III (SAGE III) has been selected for definition study for NASA's Polar Orbiting Platform (NPOP) and NASA's Space Station Attached Payload (SSAP). These are both part of the Agency’s Earth Observing System (Eos) for making long-term observations to understand the complex processes that affect global change. SAGE III is the latest generation of SAGE flight instruments, all of which use solar occultation to make vertical profiles of aerosols, ozone, and NO2, and to detect mid- to upper tropospheric clouds. SAGE II added, as will SAGE III, the capability to measure H2O. A description of the evolution of these experiments which began with the Stratospheric Aerosol Measurement I and II (SAM I and II) missions is given in Table 1.
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Gunson, M. R., and C. B. Farmer. "Overview of Atmos Results from Spacelab 3." In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/orsa.1990.mc2.
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The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment is an investigation of the distribution of neutral constituents in the earth’s atmosphere. The ATMOS instrument is a Michelson interferometer, with a response to radiation in the near- to mid-infrared, designed to make observations from on board the space shuttle in the solar occultation mode.1,2 Its first flight was made as part of the Spacelab 3 (SL-3) payload which flew on the shuttle "Challenger" between April 29 and May 6, 1989. The ATMOS experiment gathered data during 20 occultation events; 13 sunset occultations located between 26° - 34°N latitudes and 7 sunsets around 48°S.1,2 The data returned was composed of over 1000 high resolution infrared spectra containing absorption features of the earth’s atmosphere, spanning tangent heights from the ground up to 150 km, and a like number of high sun reference spectra. The spectra obtained within each occultation have been analyzed for the concentration height profiles of more than 25 different atmospheric species, including the first detection and confirmation of the presence of several gases.
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Bower, D., M. Bielski, E. Mangan, D. Schell, K. Ghahremani, and D. Gee. "Achieving Climate Control With Renewable Energy." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10751.
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Abstract The purpose of this project was to explore the feasibility of powering a climate control system solely from a renewable energy source. The off-the-shelf cooling system components were taken from a ca. 1986 R-12 residential refrigerator and then reassembled onto a custom enclosure which was constructed to serve as the climate-controlled compartment. The enclosure design was purposefully simple: a rectangular shaped box constructed out of plywood and mounted on wheels together with a plexiglass door which was substituted for the front face. The overall design provided for enhanced mobility while also allowing for easy observation of the interior temperature via an interior-mounted, digital, commercial residential thermostat integrated into the control system. The system, nominally, is triggered by incident solar radiation; the initial set-point temperature was 21 °C. Compressor power was derived solely from renewable energy. Specifically, a pair of 100W 12V monocrystalline silicon photovoltaic solar panels was used to generate electricity which was subsequently stored in a deep-cycle battery. Under steady-state AC operation, the compressor draws approximately 2.1A. Due to system inefficiencies, the corresponding DC current draw is necessarily higher and approaches 22.3A. For a compressor duty cycle ranging from 50–100%, the current draw over a model 9 hr day would range from between 100.1–200.3 A-H. The lower limit is within the energy storage capacity for the fully-charged system, as currently designed.
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Yang, Shu, and Cornel Sultan. "Free Vibration and Modal Analysis of a Tensegrity-Membrane System." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-59292.
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The growing interest in lightweight, deployable, and adaptive space membrane systems motivates the study of tensegrity-membrane systems. Such systems, which are composed of membranes, bars, and tendons, can be treated as extensions of classical tensegrity systems. Therefore, they inherit typical advantages of tensegrity systems, such as reduced mass, extreme flexibility, and the capacity of shape change. Membranes can be part of a certain device, such as a reflector or solar sail, while also offering opportunities for integrated system design. This paper presents a study in the modal analysis and free vibration analysis of a tensegrity-membrane system. Two mathematical models are used in this analysis: a nonlinear finite element model and a control-oriented model. The nonlinear finite element model is of great generality, while several modeling assumptions are introduced in the control-oriented model to simplify the modeling problem and lead to a model that lends itself to modern control design. Numerical results given by the two models are compared in order to ascertain the extent to which the two models agree. Observations related to system mode shapes, coupled dynamic behavior between system components, and system free vibration responses are discussed.
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Shamlooh, Mohamed, Ahmed Hamza, Ibnelwaleed A. Hussein, Mustafa S. Nasser, and Saeed Salehi. "Investigation on the Effect of Mud Additives on the Gelation Performance of PAM/PEI System for Lost Circulation Control." In SPE Europec featured at 82nd EAGE Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/205184-ms.
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Abstract Lost circulation is one of the most common problems in the drilling of oil and gas wells where mud escapes through natural or induced fractures. Lost circulation can have severe consequences from increasing the operational cost to compromising the stability of wells. Recently, polymeric formulations have been introduced for wellbore strengthening purposes where it can serve as Loss Circulation Materials (LCMs) simultaneously. Polymeric LCMs have the potential to be mixed with drilling fluids during the operation without stopping to avoid non-productive time. In this study, the significance of most common conventional mud additives and their impact on the gelation performance of Polyacrylamide (PAM) / Polyethyleneimine (PEI) has been investigated. Drilling fluid with typical additives has been designed with a weight of 9.6 ppg. Additives including bentonite, barite, CarboxyMethylCellulose (CMC), lignite, caustic soda, desco, and calcium carbonate has been studied individually and combined. Each additive is mixed with the polymeric formulation (PAM 9% PEI 1%) with different ratios, then kept at 130°C for 24 hrs. Rheological performance of the mature gel has been tested using parallel plate geometry, Oscillatory tests have been used to assess the storage Modulus and loss modulus. Moreover, the gelation profile has been tested at 500 psi with a ramped temperature to mimic the reservoir conditions to obtain the gelation time. The gelation time of the polymer-based mud was controllable by the addition of a salt retarder (Ammonium Chloride), where a gelation time of more than 2 hours could be achieved at 130°C. Laboratory observations revealed that bentonite and CMC have the most effect as they both assist in producing stronger gel. While bentonite acts as a strengthening material, CMC increases the crosslinking network. Bentonite has successfully increased the gel strength by 15% providing a storage modulus of up to 1150 Pa without affecting the gelation time. This work helps in better understanding the process of using polymeric formulations in drilling activities. It provides insights to integrate gelling systems that are conventionally used for water shut-off during the drilling operation to replace the conventional loss circulation materials to provide a higher success rate.
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Tyagi, Pawan. "Spin Photovoltaic Effect on Molecule Coupled Ferromagnetic Films of a Magnetic Tunnel Junction." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-63866.
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Economical solar energy harvesting can be boosted by the discovery of fundamentally new photovoltaic mechanism, and a suitable system to realize it with commonly available materials. One promising route is to focus on spin property of the electron, not charge, and develop spin photovoltaic effect with widely available ferromagnetic metals like iron and nickel. This paper reports the observation of photovoltaic effect on the molecular spintronics device composed of a magnetic tunnel junctions (MTJ) testbed and organometallic molecular clusters (OMCs). Our MSDs were produced by bridging the OMC channels between the ferromagnetic films of a prefabricated MTJ testbed with exposed side edges. The MTJ testbed exhibited OMC induced strong increase in exchange coupling and photovoltaic effect. Control experiments on isolated ferromagnetic films, same as utilized in the MTJ testbed, suggested that OMCs neither affected the magnetic properties nor produced any photovoltaic effect. Photovoltaic effect was only observed on the pair of ferromagnetic films serving as magnetic electrodes in a MTJ. Our recent Monte Carlo simulations and multiple magnetic characterizations provide evidence that molecules induced strong coupling between two ferromagnetic films can dramatically alter the overall magnetic properties of a MTJ; presumably making an ordinary MTJ suitable for spin based photovoltaic effect. The photovoltaic effect on our molecular spintronics devices (MTJ+OMCs) was sensitive towards the external magnetic field and temperature. Present paper motivates further studies to understand the spin photovoltaic effect in molecular spintronics devices.