Dissertations / Theses on the topic 'Emissivité de la surface terrestre'
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Jiang, Geng-Ming. "Retrievals of land surface emissivity and land surface temperature from MSG1-SEVIRI data." Université Louis Pasteur (Strasbourg) (1971-2008), 2007. https://publication-theses.unistra.fr/public/theses_doctorat/2007/JIANG_Geng-Ming_2007.pdf.
Jiang, Geng-Ming Li Zhao-Liang. "Retrievals of land surface emissivity and land surface temperature from MSG1-SEVIRI data." Strasbourg : Université Louis Pasteur, 2008. http://eprints-scd-ulp.u-strasbg.fr:8080/848/01/JIANG_Geng_Ming_2007.pdf.
Qiu, Shi. "Retrieval of land surface emissivity from AMSR-E and SEVIRI data." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD047/document.
This thesis focused on the retrievals of Land Surface Emissivity (LSE) from microwave data and thermal infrared data. (1) This thesis provides a method to retrieval LSE from the AMSR-E (Advanced Microwave Scanning Radiometer-Earth Observing System) and develops a Soil-Atmosphere Radiative Transfer Model (SARTM) to simulated brightness temperatures at satellite level. SARTM model is built from MonoRTM (MONOchromaticRadiative Transfer Model) and from AIEM (Advanced Integral Equation Model) models. In this study, the LSEs over whole China of year 2006 are estimated. (2) This thesis also presents an improved algorithm to retrieve LSE from SEVIRI (Spinning Enhanced Visible and Infrared Imager) data onboardthe MSG-2 satellite. Finally, this improved algorithm is applied to several MSG-2/SEVIRI datasets over a study area withinthe Iberian Peninsula region. It is demonstrated with some detailed cases that these improvements on the original LSE/land surface temperature (LST) retrieval methods are effective and reasonable
Ren, Huazhong. "Modelling of directional thermal radiation and angular correction on land surface temperature from space." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00967047.
Alalam, Perla. "Étude des aérosols à partir de mesures en laboratoire et IASI : application aux déserts d'Asie de l'Est." Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR052.
East Asia is the second largest source of mineral-type aerosols in the world after the Sahara. These can modify the Earth's radiative balance due to their properties of absorption and diffusion of atmospheric radiation. Therefore, precise information on the physico-chemical properties of desert dust is essential to understand and better quantify their impact on the atmosphere. In this context, this thesis aims to test the potential of a new methodological approach combining laboratory measurements and satellite remote sensing for better characterization of aerosols from desert and semi-arid surfaces. Its application concerns studying desert storm events in East Asia from the IASI space instrument.One of the major difficulties of this work comes from the fact that the mineral dust emitted in this region is emitted mainly above the continental surface and in the lower troposphere, which poses constraints linked, on the one hand, to a low sensitivity due to a lack of thermal contrast and on the other hand due to the great influence and variability of the Earth's surface emissivity (LSE). Thus, the first part of this work focused on improving the consideration of LSE by developing a new methodology from a set of average monthly emissivity data.Then, experimental extinction coefficients of pure minerals were linearly combined to reproduce a spectrum of Gobi dust, which made it possible to obtain the mineralogical mass fractions. In addition, from the IASI radiances, an optical thickness of Gobi dust was calculated, displaying characteristics identical to those measured in the laboratory. The linear combination of pure mineral spectra was then applied to IASI optical thickness, providing mineralogical mass fractions. Finally, the entire methodology was applied to two dust events during two different seasons and years: May 2017 and March 2021. The method made it possible to obtain the first spatial and temporal distributions of the chemical composition of desert aerosols. The average mass fractions obtained for particles from the Gobi Desert, Taklamakan Desert, and Horqin Sandy Land are close to mass fractions from the literature. In addition, these results on the chemical composition made it possible to link aerosols' spatial variability to dust emission sources, confirmed using a retro-trajectory model. In addition, comparing two IASI instruments on MetOp A and B showed good consistency, allowing us to consider the method's applicability to different MetOp platforms having the same instrument type. The results presented in this manuscript represent an important advance in improving the characterization of desert aerosols by space remote sensing, in particular concerning the analysis of the chemical composition
Li, Hongkun. "Emissivité et réflectivité infrarouges de la surface de mer avec ombre et réflexions multiples." Nantes, 2012. http://archive.bu.univ-nantes.fr/pollux/show.action?id=77806c7d-1be5-4daa-a079-73cc3e7d9cc9.
Sea surface infrared emissivity and reflectivity are important parameters in oceanic remote sensing, e. G. For deriving the sea surface temperature. They are both nearly constant for observation directions near zenith, but they vary largely for large grazing angles, because of the surface roughness. This thesis aims at calculating the sea surface infrared emissivity and reflectivity with accuracy. In addition, polarization is taken into account. Indeed, the phenomena of shadowing and multiple surface reflections are taken into account in the models through illumination functions without and with surface reflections. In order to validate developed models, a reference method, based on a Monte Carlo ray tracing algorithm, is used. Simulation results show very good agreements of the models with the ray tracing algorithm. Moreover, the agreement with emissivity measurements of the literature is improved if one surface reflection is considered. The criterion of energy conservation is better met by taking the sea surface reflections into account in the model. Thus, these results clearly show the usefulness of considering shadowing and surface reflections in the modeling
Eymin-Petot-Tourtollet, Céline. "Etude des mouvements à la surface du noyau terrestre." Paris, Institut de physique du globe, 2004. https://tel.archives-ouvertes.fr/tel-00007173.
In order to study the dynamics of the Earth's outer core, we compute core surface flows from observations of the main magnetic field. The relevance of these computations is confirmed by the similarities of the flows obtained with two independent methods and the results of different synthetic tests. Two different kind of observations are used : ground-based observations for the time period 1590-1990 and recent high-resolution satellite observations. We thus obtain a time series of the historical flows as well as a detailed model of the present flow. The evaluation of errors associated to these flows enable us to identify their reliable features. The velocity fields we obtain are in good agreement with different phenomena appearing in 3D-simulations of core dynamics. We also show that geomagnetic jerks have an explicit signature in core surface dynamics. In the last chapter, a variational data assimilation method for the study of the Earth's core is introduced
Adenis, Alice. "Imagerie tri-dimensionnelle de l'atténuation sismique du manteau terrestre." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN037/document.
The aim of this study is to build a 3-D attenuation model of Earth's upper-mantle using a unique datasetbuilt by Debayle & Ricard (2012). This dataset is among the largest in the world: more than 375,000seismograms were analyzed to extract Rayleigh-wave attenuation and velocity measurements for thefondamental mode and the five first harmonics between 40 and 240 s periods.First, attenuation measurements are processed to extract the effects of geometrical attenuation and offocusing and defocusing, in order to minimize the influence of errors on the seismic source, to avoidpotentially incorrect data, and to cluster redondant measurements. Then, measurements are regionalizedto obtain Rayleigh-wave maps for each mode and each period. The last step is the inversion of thesemaps to obtain the depth dependent attenuation. Eventually, we obtain QsADR17, a 3-D model of Swaveattenuation in the upper mantle.QsADR17 is correlated with surface tectonics down to 200 km depth, with low attenuation under thecontinents and high attenuation under the oceans. High-attenuation anomalies are found under oceanicridges down to 150~km depth, and under most of the hotspots at larger depth down to the transitionzone. A large high-attenuation anomaly at 150~km depth under the Pacific ocean suggest that thermalplumes pound into the asthenosphere. We also detect compositional heterogeneities at the base of thecratons and in active areas
Kanani, Keyvan. "Utilisation de la très haute résolution spectrale pour la mesure en environnement extérieur de l'émissivité de surface dans la bande infrarouge 3-13 Mum : Méthodes et validation expérimentale." Université Louis Pasteur (Strasbourg) (1971-2008), 2005. https://publication-theses.unistra.fr/public/theses_doctorat/2005/KANANI_Keyvan_2005.pdf.
Emissivity is an optical property of materials, related to their ability to emit electromagnetic radiation. This PhD is devoted to retrieving emissivities of outdoor surfaces from high spectral resolution (4cm-1) spectroradiometric measurements at ground level, in the 750 cm-1 to 3500 cm-1 (3-13µm) spectral range. The main objective of this work, which combines theoretical and experimental approaches, is to define and assess a methodology. Two emissivity-temperature separation techniques are addressed, the Spectral Smoothness Method (SpSm) and the Multi-Temperatures Method (MTM), with particular attention paid to extending their usual domain of application on the short wavelength side beyond 1250cm-1. Sources of errors are identified and an experimental approach to mitigate errors on the determination of the irradiance of the surface is proposed. A new method, named Smoothness and Continuity (SmaC), is introduced, which takes into account the directional behaviour of the observed surface, to improve emissivity retrieval in the mid-infrared band (MWIR from 2000 to 3000 cm-1)To quantitatively assess the retrieval methods and validate the measurement protocol, a field campaign, that took place in June 2004, aimed at providing an error budget of the methods by measuring emissivities of several samples at different times of day. SpSm, applied to the campaign measurements, provides very good results in the LWIR band (from 750 to 1300 cm-1). In the MWIR band, systematic spectral discontinuities and deviations to laboratory measurements are observed in the retrieved spectra. This is interpreted as a manifestation of angular dependence of emissivity: the new SmaC method, through the introduction of a surface form factor, leads to significantly improved results. The standard deviation of the retrieved emissivity spectra over all measurements and samples is less than 0. 01 in LWIR and less than 0. 03 in MWIR. MTM results are less satisfactory than SpSm ones, due to ill-conditioned system of equations. Finally, a numerical analysis is carried out to confirm and validate SmaC hypothesis and findings
Givri, Jacques. "Etude du rayonnement de la surface terrestre par teledetection a l'echelle climatologique." Rennes 1, 1990. http://www.theses.fr/1990REN10011.
Malaplate, Alain. "Radiométrie infrarouge : Développement et validation de méthodes utilisant la bande [3-5um] pour la détermination des paramètres de surface à haute résolution spatiale." Université Louis Pasteur (Strasbourg) (1971-2008), 2001. http://www.theses.fr/2001STR13227.
Eymin, Céline. "Etude des mouvements à la surface du noyau terrestre : du 17ème au 21ème siècle." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2004. http://tel.archives-ouvertes.fr/tel-00007173.
historiques et un modèle détaillé des mouvements actuels sont obtenus. L'estimation des marges d'erreurs associées permet d'identifier les structures fiables. Nos reconstructions sont en accord avec différents phénomènes mis en évidence par des modélisations 3D du noyau. Nous montrons aussi que les jerks géomagnétiques ont une signature dynamique très nette. Enfin, nous posons les bases d'une méthode d'assimilation variationnelle de données adaptée à l'étude du noyau.
Vincensini, Anaïs. "Contribution de IASI à l’estimation des paramètres des surfaces continentales pour la prévision numérique du temps." Thesis, Toulouse, INPT, 2013. http://www.theses.fr/2013INPT0127/document.
The Infrared Atmospheric Sounding Interferometer (IASI), on-board the EUMETSAT Polar System Metop satellite, is developed by CNES in the framework of a co-operation agreement with EUMETSAT. IASI enables, amongst other, infrared soundings of temperature, moisture and retrievals of surface parameters. However in the numerical weather prediction context, these observations are not as intensively used over land as they are over sea because of larger uncertainties about land emissivity and land surface temperature (LST). These uncertainties have an impact on the quality of radiative transfer simulation and hinder the use of these measurements in numerical weather prediction models. Only channels that are not sensitive to the surface are currently assimilated in operations, which limits the potential of sounding instruments to the highest atmospheric layers. This PhD aims to improve the description of land surface parameters in the ARPEGE global model of Météo-France to assimilate IASI data over land. First of all, we tried to improve the surface modelling (surface emissivity and LST) over land in the ARPEGE model. To this end, two emissivity atlases were integrated in this model. The first one is the emissivity climatology computed from the IASI Level-2 products from EUMETSAT and the second one is the global high spectral resolution infrared land surface emissivity database (called UWIREMIS) developed by the Space Science and Engineering Center at University of Wisconsin. Hence, the LST was retrieved from IASI surface channels using these atlases as input parameters in the radiative transfer model. These LSTs were compared to land LST products: the MODIS (Moderate-Resolution Imaging Spectroradiometer) products from the NASA and the IASI Level-2 products from EUMETSAT. These comparisons enabled us to choose the IASI channel combination that provided the best LST estimates. The use of a realistic surface modelling contributed to improve the quality of radiative transfer simulations for surface sensitive channels. Then, surface sensitive IASI radiances were assimilated over land in ARPEGE in clear sky conditions using the surface parameters as previously defined. The impact on analysis and forecast quality was studied. The use of good estimates of surface emissivity and LST significantly increased the number of assimilated observations. The main improvements are for geopotential and temperature forecasts for pressure levels lower than 400~hPa (except in the tropics and in the stratosphere). Finally, from a climatological point of view and within the more specific framework of the Concordiasi campaign, we assessed and validated the use of IASI data in Antarctica. The temperature and humidity retrieved in this particular study proved of better quality than the model profiles, as assessed against the sonde measurements. The improvement is particularly striking for surface temperature. In this framework, the LST retrieved in this PhD were compared with in situ measurements at Concordia and at South Pole station. These estimates are of a great accuracy at Concordia
Beucler, Éric. "Tomographie régionale et globale du manteau terrestre : approche par les ondes de volume et de surface." Paris 7, 2002. http://www.theses.fr/2002PA077227.
Berté, Emmanuel. "Mesure de champs thermiques de surface par thermographie bichromatique en situation de frottement haute énergie." Thesis, Ecole centrale de Lille, 2015. http://www.theses.fr/2015ECLI0033/document.
In highly dissipative contacts, the energy dissipated by friction leads to severe thermal loads which could have bad consequences on performances, on friction parts durability, on the environment or on human health. Therefore, knowledge of sliding surfaces thermal fields is a first-rate issue. Due to the lack of knowledge about the emissivity of those surfaces, which change both spatially and temporally during friction, measuring thermal fields is difficult. The work done concerned the development of thermal fields measurement by bispectral thermography, which allows to get simultaneously surface emissivity and temperature. The difficulties reside in the spatial and temporal images registration of two infrared cameras, in the camera flows calibration and in the spectral emissivity variation. The technique developed was applied to the in situ fields measurement of temperature and emissivity of a brake disc during braking. It was then used for analysis of thermal locations induced by friction and their interactions with the tribological circus, leveraging the knowledge of the spatial and temporal evolution of the emissivity
Nataf, Henri-Claude. "Éléments d'anatomie et de physiologie du manteau terrestre : tomographie sismique et convection expérimentale." Paris 11, 1986. http://www.theses.fr/1986PA112357.
The first part of this thesis presents a global map of the lateral heterogeneities in the earth's upper mantle, obtained from the inversion of the velocity anomalies of surface waves. We retrieve the lateral variations of the seismic velocities and of their anisotropy. The results are compared with specific observations on various tectonic provinces from the literature (mid-oceanic ridges, continental shields, mountains, etc. ). Shields appear to be systematically fast for S waves. Several anomalous regions are discovered. It is shown that the amplitude of the anisotropy of seismic velocities is as large as their lateral variations, and that it is necessary to account for this effect when building regional or global seismic models. The second part of this work is an analysis of convection in a fluid whose viscosity is strongly temperature-dependent. The discussion relies on laboratory experiments performed with fluids in which the viscosity varies by up to 105 across the convecting layer. A simple model is proposed, in which convection takes place under a very viscous lid which does not move. The model explains the experimental data and is used to build a realistic scheme for the thermal evolution of the planets. One of the limitations of the model is that it does not explain the 'plate tectonics' regime observed on the earth. Ways are proposed to remedy for that. The conclusion is a synthesis of the results obtained in the first two parts, concerning the 'anatomy' and the 'physiology' of the earth's mantle. We discuss the stratification of convection in the mantle into one or two layers, and we speculate about the origin of 'hot spots'
Browaeys, Julien. "Les ferrofluides : ondes de surface, résistance de vague et simulation de la convection dans le manteau terrestre." Phd thesis, Université Paris-Diderot - Paris VII, 2000. http://tel.archives-ouvertes.fr/tel-00007235.
Browaeys, Julien. "Les ferrofluides : ondes de surface, résistance de vague et simulation de la convection dans le manteau terrestre." Phd thesis, Paris 7, 2000. https://tel.archives-ouvertes.fr/tel-00007235.
Silva, Luís Alexandre. "Ecoulements à la surface du noyau, secousses géomagnétiques et prédictions à court terme du champ magnétique terrestre." Paris, Institut de physique du globe, 2010. http://www.theses.fr/2010GLOB0002.
This thesis reports on a series of investigations directed towards the dual goal of improving our understanding of what drives the time evolution of the Earth's main magnetic field, and of improving our current ability to predict its short-term behavior. For that we first perform core flow inversions for several epochs and compute first estimates of the flow acceleration by computing differences between successive flows. These first results suggest that the flow generating the Secular Variation (SV) is not stationary. Next, we show how both the core flow and core flow acceleration can be computed simultaneously at any given epoch, if the field and its first and second time derivatives (the SV and the Secular Acceleration (SA)) are known. This allows us to unambiguously show that no stationary flow can account for the observed SA. Based on those results, we consider the possibility of improving on the short-term prediction of the field based on a linear extrapolation currently used by the International Geomagnetic Reference Field (IGRF) by using a method based on a steadily accelerated flow. Then we independently consider the possibility of increasing the spatial resolution of the predictive SV model currently used by IGRF. From all of the above, we conclude that the main limitation to shortterm predictions of the field is the occurrence of sudden changes in the SA (geomagnetic jerks). We thus investigate the type of core ow acceleration changes that are needed to account for those jerks and focus on the 2003 ge
Vaitilingom, Laurent. "Diffusion bistatique des ondes EM par une surface rugueuse en HF : application aux fouillis maritime et terrestre." Brest, 2011. http://www.theses.fr/2011BRES2030.
The use of HF radar is interesting because it can cover a larger area than a classical radar which is limited by electromagnetic horizon. However, the use of such radar is not easy because, in this frequency band, antennas are huge and ionospheric and surfacic clutters disturb the task of the radar. In order to improve the EM wave processing in HF band, we focus on the EM characterization of surfacic clutter in HF hand. In that respect, we concentrate on an estimation of EM signature in HF band of sea and ground clutter. First, we study EM scattering models which are generally used in frequencies between 1 and 20 GHz. We outline the hypothesis of approximate models which enable us to calculate EM scattering coefficients. We establish the validity domains of models, and the types of surface upon these models can be applied. We also examine the expressions of scattering coefficient estimated in specific configurations (monostatic, forward scattering and bistatic). Then, to apply the scattering models considered on sea and ground surfaces, we analyse geometrical and physical characterization tools for different types of surfaces. Finally, we analyse the effects, on scattering coefficients, of parameters liked to the studied surface (wind speed and wind direction, temperature and salinity of salt water, Doppler frequency for sea surface; composition and roughness for ground surface), of biostatic geometry parameters and of incident frequency. The methodology adopted in this work to study scattering coefficients estimated by different models and applied on natural surfaces combines both aspects of modeling and simulation and it is evaluated in comparison with results published in open literature
Dicezare, Marília Takaguti. "Caracterização da elevação do Rio Grande a partir de elementos do campo de gravidade terrestre." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/14/14132/tde-15052018-172757/.
Satellite altimetry data contain important information for mapping tectonic structures in oceanic regions, such as faults, fracture zones and seamounts. The great availability and spatial density of these data allow one to identify ocean floor features with good accuracy. This work aims to investigate structural characteristics of the Rio Grande Rise, in South Atlantic, through elements of the terrestrial gravity field. We used sea surface height (SSH) data from satellite missions ERS1-GM, Geosat-GM and Seasat to calculate sea surface gradients (SSG), which are the SSH directional derivative along the ascending and descending satellite tracks. SSG emphasize the short wavelengths associated with the important oceanic features studied. Geoid gradients (deflection of the vertical) were also calculated to assist in the interpretation of the SSG signal. By analyzing sea surface heights, it is possible to identify larger structures, such as the rift of the rise, some fractures and large seamounts. In contrast, sea surface gradients provide greater details of the features characterized by the SSH and the entire area, also revealing several smaller seamounts. The positioning of the structures identified by both SSH and SSG is fairly accurate. However, factors such as direction and orientation of the satellite tracks and the presence of adjacent structures may influence the SSG response to a given tectonic feature. For this reason, the ascending and descending tracks of the three satellites may have different responses. Therefore, it is recommended that one analyzes the two sets of tracks from the several altimetric missions to obtain more information on the structural characteristics of the features. The study also allowed us to identify possible structures with a characteristic response of seamounts on SSH descending tracks, which were not previously characterized in the literature and do not have a similar correspondent in topographic/bathymetric models.
Béland, Martin. "Estimation de paramètres structuraux des arbres dans une savane à partir de mesures LiDAR terrestre et d'imagerie à très haute résolution spatiale." Thèse, Université de Sherbrooke, 2011. http://savoirs.usherbrooke.ca/handle/11143/2849.
Chevalier, Laure. "Facteurs influençant la composition du régime alimentaire de l'escargot petit-gris Hélix aspersa Müller (gastéropode terrestre)." Rennes 1, 2001. http://www.theses.fr/2001REN10099.
Chambodut, Aude. "Le champ magnétique terrestre : structures spatiales et variations temporelles vues par les ondelettes." Paris, Institut de physique du globe, 2004. https://tel.archives-ouvertes.fr/tel-00008021.
Zhong, Xinke. "Methodological developement for retrieving land surface temperature from hyperspectral thermal infrared data." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD014/document.
Land surface temperature (LST) is an important parameter in climate systems. Hyperspectral thermal infrared (TIR) data, containing large information about the surface and the atmosphere, is an important source of information for retrieving LST by remote-sensing
Camargos, Carla Cristina de Souza. "Desempenho de um algoritmo de otimização hierárquico multiobjetivo aplicado a um modelo de superfície terrestre e ecossistemas." Universidade Federal de Viçosa, 2013. http://locus.ufv.br/handle/123456789/5261.
Conselho Nacional de Desenvolvimento Científico e Tecnológico
The performance of LSEMs (Land surface and ecosystem models) depends on the parameters of the equations representing the simulated process. However, the measurement of some parameters can be impractical or even impossible; therefore, they need to be estimated, or preferably optimized specifically for each ecosystem. When the parameters are calibrated to a single variable (mono-objective problem) they may not represent the reality, because the complexity of the model and its dependence on several variables (multi-objective problem). Thus, simultaneous multi-objective optimizations are indispensable. However, the optimization performance decreases as the number of variables to be optimized simultaneously increases. Furthermore, the study of simultaneous optimization using more than three objectives is a new area and not yet sufficiently studied. For simultaneous optimization of a large number of variables, there is a method that uses concepts of hierarchical systems theory in which the optimization occurs from the fastest (radiative fluxes) to the slowest process (carbon allocation). This study evaluates the performance of the hierarchical optimization using the index D (the average of the ratios between the individual outputs of multi-objective optimization and monoobjective). Understanding how the performance index D varies with respect to the number of objective functions optimized and to the number of hierarchical levels is important for the development of this research area. Two steps are necessary to achieve the study goals. First, a sensitivity analysis was performed to determine the output variables sensitivity to the model parameters. After, simulations were made using all possible combinations among the seven micrometeorological variables available (PARo, fAPAR, Rn, u *, H, LE, NEE) taking into account the hierarchy of processes. The results indicate that for up to three objective functions, hierarchical multi-objective optimization generates better results than the simultaneous multiobjective optimization (one hierarchical level), provided that the parameters distribution among hierarchical levels is consistent with the sensitivity analysis. Another important result shows that for the same number of outputs optimized, the greater the number of hierarchical levels the better the performance of the optimized model. However, the model performance falls quickly as the number of objective functions increases, evidencing that the power of hierarchy calibration that use a high number of objective functions is highly dependent on the removal of some constraints for model s performance.
O desempenho de um LSEM (Modelo de superfície terrestre e ecossistema) depende dos parâmetros das equações que representam os processos simulados. Contudo, a mensuração de alguns destes parâmetros pode ser impraticável ou até mesmo impossível; por isso, necessitam ser estimados ou, preferencialmente, otimizados para cada ecossistema. Quando os parâmetros são calibrados para uma única variável (problema mono-objetivo) eles podem não representar bem a realidade, dado a complexidade do modelo e sua dependência de diversas variáveis (problema multiobjetivo). Por isso, há a necessidade de uma otimização simultânea multiobjetiva. Porém, o desempenho da otimização diminui com o aumento do número de variáveis otimizadas simultaneamente e, além disso, o estudo da otimização simultânea de mais de três objetivos é uma área relativamente nova e não suficientemente estudada. Para a otimização simultânea de um grande número de variáveis, existe uma metodologia na qual se utiliza conceitos de teoria hierárquica de sistemas em que a otimização ocorre dos processos mais rápidos (fluxos radiativos) para os mais lentos (alocação de carbono). Este trabalho avalia o desempenho da otimização hierárquica do modelo, utilizando o índice D (a média das razões individuais entre as saídas das otimizações multiobjetiva e monoobjetiva). Entender como o índice de desempenho D do algoritmo de otimização hierárquico varia em relação ao número de funções objetivo otimizadas é de extrema importância para o desenvolvimento desta área de pesquisa. Para fazer atingir os objetivos, foram necessárias duas etapas. Primeiramente, foi feita uma análise de sensibilidade, a fim de conhecer a sensibilidade das variáveis de saída aos parâmetros do modelo. Depois, foram feitas simulações com todas as combinações possíveis entre as sete variáveis micrometeorológicas disponíveis (PARo, fAPAR, Rn, u*, H, LE, NEE) levando em consideração a hierarquia dos processos. Os resultados encontrados indicam que, para até três funções objetivo, a otimização multiobjetiva hierárquica pode gerar resultados melhores do que a otimização multiobjetiva tradicional (um único nível hierárquico), desde que a distribuição dos parâmetros entre as variáveis seja feita de forma coerente com a análise de sensibilidade. Outro resultado importante revela que para um mesmo número de saídas otimizadas, quanto maior o número de níveis hierárquicos melhor o desempenho do modelo otimizado. Porém, o desempenho do modelo diminui rapidamente quando o número de funções objetivo aumenta, evidenciando que o poder da calibração hierárquica para o uso de um grande número de funções objetivo é altamente dependente de algumas restrições que o modelo possui e um alto desempenho do modelo para muitas funções objetivo será possível somente após a remoção delas.
Sun, Yan. "Simulation du cycle biogéochimique du phosphore dans le modèle de surface terrestre ORCHIDEE : évaluation par rapport à des données d'observation locales et mondiales." Electronic Thesis or Diss., université Paris-Saclay, 2021. http://www.theses.fr/2021UPASJ001.
Phosphorus (P) plays a critical role in controlling metabolic processes, soil organic matter dynamics, plant growth and ecosystem productivity, thereby affecting greenhouse gas balance (GHG) of land ecosystems. A small number of land surface models have incorporated P cycles but their predictions of GHG balances remain highly uncertain. The reasons are: (1) scarce benchmarking data for key P-related processes (e.g. continental to global scale gridded datasets), (2) lack of comprehensive global evaluation strategy tailored for d P processes and interlinkages with carbon and nitrogen (N) cycles, and (3) insufficient model calibration limited by the high computation cost to simulate coupled CNP cycles which operate on timescales of minutes to millenia. Addressing those research gaps, I apply a combination of statistical methods (machine learning), LSMs and observational data among various scales.Firstly (Chapter 2), to address the lack of benchmarking data, I applied two machine-learning methods with the aim to produce spatial gridded maps of acid phosphatase (AP) activity on continental scale by scaling up scattered site observations of potential AP activity. AP secreted by fungi, bacteria and plant roots play an important role in recycling of soil P via transforming unavailable organic P into assimilable phosphate. The back-propagation artificial network (BPN) method that was chosen explained 58% of AP variability and was able to identify the gradients in AP along three transects in Europe. Soil nutrients (total nitrogen, total P and labile organic P) and climatic controls (annual precipitation, mean annual temperature and temperature amplitude) were detected to be the dominant factors influencing AP variations in space.Secondly (Chapter 3), I evaluated the performance of the global version of the land surface model ORCHIDEE-CNP (v1.2) using the data from chapter 2 as well as additional data from remote-sensing, ground-based measurement networks and ecological databases. Simulated components of the N and P cycle at different levels of aggregation (from local to global) are in good agreement with data-driven estimates. We identified model biases, in the simulated large-scale patterns of leaf and soil stoichiometry and plant P use efficiency, which point towards an underestimation of P availability towards the poles. Based on our analysis, we propose ways to address the model biases by giving priority to better representing processes of soil organic P mineralization and soil inorganic P transformation.Lastly (Chapter 4), I designed and tested a Machine Learning (ML)-based procedure for acceleration of the equilibration of biogeochemical cycles to boundary conditions (spinup) which is causing the low computational efficiency of current P-enabled LSMs. This ML-based acceleration approach (MLA) requires to spin-up only a small subset of model pixels (14.1%) from which the equilibrium state of the remaining pixels is estimated by ML. MLA predicts the equilibrium state of soil, biomass and litter C, N and P on both PFT and global scale sufficiently well as indicated by the minor error introduced in simulating current land carbon balance. The computational consumption of MLA is about one order of magnitude less than the currently used approach, which opens the opportunity of data assimilation using the ever-growing observation datasets.In the outlook, specific applications of the MLA approach and future research priorities are discussed to further improve the reliability and robustness of phosphorus-enabled land surface models
Picard, Bruno. "Télédétection de la surface terrestre par un radiomètre imageur à synthèse d'ouverture : principes de mesure, traitement des données interférométriques et méthodes de reconstruction régularisées." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2004. http://tel.archives-ouvertes.fr/tel-00009029.
l'Agence Spatiale Européenne, à travers son programme «Exploration de la Terre» finance
la mission spatiale SMOS (Soil Moisture and Ocean Salinity).
Elle repose, pour la première fois dans le cadre de l'observation de la Terre,
sur l'utilisation d'un radiomètre imageur à synthèse d'ouverture, technologie initialement développée
en radioastronomie.
Cette thèse est axée sur l'étude des méthodes de reconstruction régularisée permettant, à partir des données
interférométriques fournies par l'instrument, d'obtenir des cartes de températures de brillance.
Le principe de mesure diffère de celui des instruments habituellement utilisés pour l'observation
de la surface terrestre. Une première partie est donc consacrée à une introduction des mécanismes
fondamentaux de l'interférométrie passive, à travers une étude de la chaîne de mesure, d'un rappel
de l'expérience des trous d'Young et des propriétés de la transformée de Fourier à deux dimensions.
Le traitement des données interférométriques demande un cadre géométrique et algébrique rigoureux,
décrit dans une seconde partie. De plus, les radiomètres à synthèse d'ouverture étant des instruments
à bande passante limitée, il est nécessaire de faire appel à l'apodisation pour réduire les oscillations
apparaissant dans les cartes reconstruites. Les fenêtres d'apodisation sont donc caractérisées pour deux
configurations possibles du réseau d'antennes. L'estimation des paramètres géophysiques demandant
le traitement de cartes de températures de brillance définies sur des grilles régulières et
à résolution spatiale constante, nous avons introduit dans ce but des techniques de rééchantillonnage
et la possibilité d'utiliser le multi-fenêtrage.
Le problème inverse à résoudre étant mal posé, il est important de s'assurer de l'existence
d'une solution unique. C'est là l'objet de l'utilisation de méthodes de reconstruction régularisées.
Elles sont définies et comparées dans une troisième partie. Elles sont ensuite utilisées pour caractériser
plusieurs problèmes intervenant dans la reconstruction d'image pour les radiomètres imageurs à synthèse d'ouverture.
Ainsi, l'erreur systématique, qui intervient alors même qu'aucune erreur sur les données ou sur
la modélisation de l'instrument n'est introduite, est expliquée et quantifiée pour deux méthodes
de reconstruction régularisées et pour différentes scènes observées. La propagation du bruit radiométrique
sur les données fait l'objet d'un travail spécifique, ainsi que l'impact des erreurs de modélisation
subsistant suite à une auto-caractérisation, méthode présentée ici et permettant une calibration en vol
des paramètres instrumentaux. L'impact de la pollution des données interférométriques par le
rayonnement solaire sur la télédétection des océans est ensuite étudié. Enfin, la faisabilité et
la robustesse de la reconstruction en mode de polarisation totale à l'aide des méthodes de
reconstruction régularisées sont démontrées.
Sarti, Francesco. "Potentiel de la télédétection optique-radar pour le suivi des changements et déformations de la surface terrestre : application à la gestion des risques naturels." Toulouse 3, 2004. http://www.theses.fr/2004TOU30289.
The study, the application and (to a certain extent) the improvement of techniques based on spaceborne radar and optical data for surface change detection and displacement measurement have been investigated in this PhD thesis. Under specific conditions, these data can allow mapping and measuring surface changes and ground deformations associated to events such as earthquakes, subsidence, volcanic eruptions and floods. Therefore, these techniques deserve a particular interest both in a scientific context (support for the improvement of seismic and geo-hydrological models) as well as for natural risk management in an operational context (delivery of products issued from Earth Observation for the support to emergency operations and rescue organizations)
Czerniak, Marilyne. "Oxydation et recombinaison catalytique à la surface de matériaux céramiques soumis à des conditions de rentrée atmosphérique terrestre (Haute température, plasma basse pression d'air)." Bordeaux 1, 1996. http://www.theses.fr/1996BOR10535.
Araujo, Taciana Lima. "Estimativa da temperatura e do saldo de radiação à superfície terrestre em Maceió-AL utilizando imagens TM/LANDSAT 5." Universidade Federal de Alagoas, 2006. http://repositorio.ufal.br/handle/riufal/862.
Fundação de Amparo a Pesquisa do Estado de Alagoas
O trabalho proposto estima, mediante dados de imagens multiespectrais do Landsat 5- TM, índices de vegetação, albedo, temperatura da superfície terrestre e o saldo de radiação da cidade de Maceió, relacionando-os com a malha urbana. O município de Maceió, nos últimos 30 anos, teve seu crescimento areal intensificado, o que resulta substituição de áreas verdes por uma zona urbana edificada, alterando o relevo, impermeabilizando o solo, diminuindo assim a participação do fluxo de calor no solo do balanço de energia na superfície e aumentando o fluxo de calor sensível, responsável pela sensação térmica sentida. Portanto, mudanças locais causadas por edificações e ocupações inadequadas provocaram alterações no conforto urbano ambiental. As imagens utilizadas são compostas por sete bandas espectrais do Landsat 5 - TM referentes aos dias 11 de junho de 1990, 21 de setembro de 1998 e 03 de setembro de 2003. Os cálculos foram realizados com a utilização do software ERDAS 8.5. O Índice de Vegetação da Diferença Normalizada (IVDN) apresentou valores médios de 0,188 para o ano de 1990, 0,253 para 1998 e 0,242 para 2003. De acordo com os resultados houve aumento do IVDN, o que poderia levar a conclusão de que ocorreu uma intensificação da cobertura vegetal. O albedo da superfície encontrado foi de 12,06% para o ano de 2003 seguidos por 9,95% para 1998 e 9,84% para 1990, sendo este o mais baixo valor apresentando se comparado aos outros anos estudados na pesquisa. A temperatura da superfície terrestre estimada foi maior para o ano de 1998 sendo de 26,96°C seu valor médio e para os anos de 1990 e 2003 foi praticamente a mesma, sendo de 24,19°C e 24,90°C, respectivamente. Os valores instantâneos do saldo de radiação na superfície foi menor para o ano de 1990 e com médias próximas entre os anos de 1998 e 2003. Os valores obtidos foram: 586,35W/m2 para 1990, 763,06W/m2 para 1998 e 752,32W/m2 para 2003. Para a obtenção de uma avaliação mais detalhada da pesquisa seria necessário levar em consideração a topografia local pela utilização do Modelo de Elevação Digital MED.
Lefebvre, Anthony. "Simulation et conception de microsources infrarouges nanophotoniques pour la détection de gaz." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLO002/document.
Joule-heated suspended microhotplates can be used as infrared sources in cheap, low-consumption spectroscopic gas sensors. To enhance the very low efficiency of first generation structures, both their thermal and optical designs have to be optimized.The implementation of frustrated plasmonic resonators on top of the membrane grants both spectral and angular control of its emissivity. It is thus possible to make it radiate only at the frequencies absorbed by the gas under study, and in the solid angle of the detector. This leads to an increase in useful radiated power while the overall electrical consumption is decreased. Dynamical studies of membrane heating provide welcome insight on the relationship between membrane radius, heating time and energy consumption per measurement. The existence of a compromise is demonstrated in order to maximize the radiative efficiency, and its physical interpretation is detailed.Eventually, membranes fabricated in LETI’s clean room were characterized to measure their electrical, optical and mechanical properties. The implementation of such sources in a CO2 prototype sensor led to state-of-the-art results, with a few dozen ppm sensitivity with a power consumption of only one milliwatt
Soma, Maxime. "Estimation de la distribution spatiale de surface et de biomasse foliaires de couverts forestiers méditerranéens à partir de nuages de points acquis par un LIDAR terrestre." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0111.
To better understand functioning of forest ecosystems at fine scale, ecophysiological model attempt to include energy and material fluxes. Such exchanges depend on the distribution of vegetation. Hence, these models require a tridimensional (3D) description of vegetation structure, at a level of detail which can only be retrieve with remote sensing at large scale. Terrestrial LiDAR (Light Detection And Ranging) have a great potential to provide 3D description of vegetation elements in canopy. Previous studies established promising relations between the point density and quantity of vegetation. This work develop these statistical methods, focusing on source of errors. Systematic biases are corrected at branch, tree and plot scales. This study relies on both numerical simulations and field experiments. First, we test estimators on branches in laboratory conditions. On this natural vegetation, estimators are sensitive to voxel size and distance from instrument with phase-shift LiDAR. Developed corrections from this branch experiment are valid at tree scale. However, difficulties arising from sampling limitations due to occlusion and instrument sampling pattern cause negative biases in dense areas. Specific investigations are conducted to identify source of errors and to optimize multiscan estimations. A statistical method called LAD-kriging, based on spatial correlation within vegetation, improves local accuracy of estimations and limits underestimations due to occlusion. The tools produced in this work allow to map vegetation at plot scale by providing unbiased estimator of leaf area. Some of these tools are currently implemented within open access Computree software
Morel, Jules. "Surface reconstruction based on forest terrestrial LiDAR data." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0039/document.
In recent years, the capacity of LiDAR technology to capture detailed information about forests structure has attracted increasing attention in the field of forest science. In particular, the terrestrial LiDAR arises as a promising tool to retrieve geometrical characteristics of trees at a millimeter level.This thesis studies the surface reconstruction problem from scattered and unorganized point clouds, captured in forested environment by a terrestrial LiDAR. We propose a sequence of algorithms dedicated to the reconstruction of forests plot attributes model: the ground and the woody structure of trees (i.e. the trunk and the main branches). In practice, our approaches model the surface with implicit function build with radial basis functions to manage the homogeneity and handle the noise of the sample data points
Boisier, Juan Pablo. "Évaluer les impacts robustes du changement d'usage des sols sur le climat des 150 dernières années et sur le climat projeté pour le siècle prochain." Phd thesis, Ecole Polytechnique X, 2012. http://pastel.archives-ouvertes.fr/pastel-00787972.
Sabajo, Clifton. "Changements dans l’utilisation des terres et de la couverture terrestre en Asie du sud-est : les effets de la transformation sur les paramètres de la surface en Indonésie." Thesis, Paris, AgroParisTech, 2018. http://www.theses.fr/2018AGPT0005.
Over the last decades, Indonesia has experienced dramatic land transformations with an expansion of oil palm plantations at the expense of tropical forests. Indonesia is currently one of the regions with the highest transformation rate of the land surface worldwide related to the expansion of oil palm plantations and other cash crops replacing forests on large scales. As vegetation is a modifier of the climate near the ground these large-scale land transformations have major impacts on surface biophysical variables such as land surface temperature (LST), albedo, vegetation indices (e.g. the normalized difference vegetation index, NDVI), on the surface energy balance and energy partitioning.Despite the large historic land transformation in Indonesia toward oil palm and other cash crops and governmental plans for future expansion, this is the first study so far to quantify the impacts of land transformation on biophysical variables in Indonesia. To assess such changes at regional scale remote sensing data are needed.As a key driver for many ecological functions, LST is directly affected by land cover changes.We analyze LST from the thermal band of a Landsat image and produce a high-resolution surface temperature map (30 m) for the lowlands of the Jambi province in Sumatra (Indonesia), a region which experienced large land transformation towards oil palm and other cash crops over the past decades. The comparison of LST, albedo, NDVI, and evapotranspiration (ET) between seven different land cover types (forest, urban areas, clear cut land, young and mature oil palm plantations, acacia and rubber plantations) shows that forests have lower surface temperatures than the other land cover types, indicating a local warming effect after forest conversion. LST differences were up to 10.1 ± 2.6 ºC (mean ± SD) between forest and clear-cut land. The differences in surface temperatures are explained by an evaporative cooling effect, which offsets an albedo warming effect.Young and mature oil palm plantations differenced in their biophysical. To study the development of surface biophysical variables during the 20 – 25 years rotation cycle of oil palm plantations, we used three Landsat images from the Jambi province in Sumatra/Indonesia covering a chronosequence of oil palm plantations.Our results show that differences between oil palm plantations in different stages of the oil palm rotation cycle are reflected in differences in the surface energy balance, energy partitioning and biophysical variables. During the oil palm plantation lifecycle the surface temperature differences to forest gradually decrease and approach zero around the mature oil palm plantation stage of 10 years. Concurrently, NDVI increases and the albedo decreases approaching typical values of forests. The surface energy balance and energy partitioning show a development patterns related to biophysical variables and the age of the oil palm plantations. Newly established and young plantations (< 5 years) have less net radiation available than mature oil palm plantations, yet have higher surface temperatures than mature oil palm plantations. The changes in biophysical variables, energy balance and energy partitioning during the oil palm rotation cycle can be explained by the previously identified evaporative cooling effect in which the albedo warming effect is offset. A main determinant in this mechanism is the vegetation cover during the different phases in the oil palm rotation cycle. NDVI as a proxy for vegetation cover showed a consistent inverse relation with the LST of different aged oil palm plantations, a trend that is also observed for different land use types in this study. (Last and final summary in the thesis)
Sajjad, Naheed. "Bistatic scattering of electromagnetic waves from rough surface by using second order twoscale model : application to sea and bare soil surface." Brest, 2011. http://www.theses.fr/2011BRES2049.
L’estimation de la surface équivalente radar (SER) des fouillis de mer et terrestre est essentielle pour la conception et l’amélioration des performances des systèmes de télédétection et d’observation de la planète. Le problème particulier de la diffusion des ondes en configuration à angle rasant est de grand intérêt à cause de son importance pour la surveillance, suivi de cible, la communication et les systèmes de navigation fonctionnant au-dessus de surfaces rugueuses, terrestre ou maritime. La surface équivalente radar d’une surface rugueuse devient très faible en incidence rasante puisque la plus grande partie de la puissance incidente est diffusée dans la direction spéculaire (selon le degré de rugosité de k surface). De plus, les mécanismes principaux de diffusion sont différents aux angles rasants, par exemple, les effets de diffusion multiple (ou de diffusion d’ordre supérieur), l’ombrage, fading et les mécanismes liés au déferlement des vagues sont particulièrement présents dans une telle configuration. Par conséquent, c’est dans ce contexte que s’intègre les travaux de recherche développés dans cette thèse. Ceci en développant le modèle deux échelles à l’ordre 2 (TSM2) permettant ainsi de contribuer à l’estimation des coefficients de diffusion bistatique par les surfaces rugueuses avec l’application de ce modèle aux surfaces maritime et terrestre. L’évaluation du modèle développé est réalisée en effectuant des comparaisons par rapport aux résultats obtenus avec d’autres modèles et aussi aux données issues de la littérature ouverte
Karbou, Fatima. "Inversion des mesures radiométriques haute-fréquence au-dessus des surfaces continentales." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2004. http://tel.archives-ouvertes.fr/tel-00524882.
Sayão, Veridiana Maria. "Land surface temperature and reflectance spectra integration obtained from Landsat on the soil attributes quantification." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-20032018-112133/.
Os atributos do solo influenciam diretamente na sua temperatura de superfície. Apesar de existir vários estudos utilizando espectros de solos obtidos de satélite, a avaliação do solo por meio da Temperatura de Superfície Terrestre (em inglês Land Surface Temperature, LST) ainda é escassa. A ampla disponibilidade de dados termais de satélite e o desenvolvimento de algoritmos para derivar a LST facilitou o seu uso em estudos de solos. O objetivo desse trabalho foi avaliar variações da LST do solo devidas à sua composição e verificar o potencial de uso da LST na quantificação de atributos do solo, também integrada com dados de espectros de reflectância e elevação. A área de estudo (198 ha) está localizada no estado de São Paulo, Brasil, e estava com solo exposto e arado na data de aquisição da imagem de satélite. Amostras de solo foram coletadas em um grid regular de 100 x 100 m (profundidades: 0.02 m e 0.8-1.0 m); a granulometria do solo, matéria orgânica (MO) e óxidos de ferro foram determinados via análises físicas e químicas laboratoriais. Neste estudo, uma imagem do Landsat 5 foi utilizada para extrair a temperatura de superfície usando a inversão da função da Lei de Planck na banda 6 (10.400 - 12.500 nm), e a emissividade de superfície foi estimada utilizando o método do limiar do Índice de Vegetação da Diferença Normalizada. Valores de reflectância das bandas 1, 2, 3, 4, 5 e 7 foram extraídos. Modelos para quantificação de atributos do solo foram feitos usando Regressão Linear (RL), com amostras de 62 pontos de tradagem distribuídos em 14 topossequências. A RL simples foi aplicada para gerar modelos de predição baseados na LST e também na elevação (extraída de um modelo digital de elevação). A RL múltipla foi aplicada para gerar modelos de predição usando os espectros de reflectância com correção atmosférica das bandas do Visível, Infravermelho próximo e Infravermelho de ondas curtas (Vis-NIR-SWIR) como preditores; também foi aplicada para predição de atributos do solo usando simultaneamente dados do Vis-NIR-SWIR, LST e elevação, e apenas variáveis significativas identificadas por teste T foram usadas. A performance preditiva dos modelos foi avaliada baseada no coeficiente de determinação ajustado (R2adj), raiz do erro quadrático médio (RMSE, g kg-1) e razão de desempenho do intervalo interquartil (RPIQ) obtidos na validação. A krigagem ordinária também foi feita e as superfícies interpoladas resultantes foram comparadas com o melhor modelo de RL. Houve correlação significativa entre os atributos do solo e dados de reflectância, LST e elevação, e solos com textura argilosa foram diferenciados de solos arenosos com base em valores médios de LST. Para todos os atributos do solo, os modelos usando apenas elevação apresentaram a pior performance, modelos usando somente LST, performance moderada, e usando as bandas do Vis-NIR-SWIR, boa performance preditiva. Para argila, o melhor modelo obtido teve as bandas 4-7, LST e elevação como preditores; para areia e óxidos de ferro, o melhor modelo teve as bandas 4-7 e LST; para MO, banda 4, banda 7 e LST. O uso da LST para estimar atributos do solo aumenta a performance preditiva de modelos de RL múltipla quando associada a outras variáveis obtidas via sensoriamento remoto (SR), particularmente dados de reflectância de superfície, melhorando a validação dos modelos atingindo altos valores de R2adj e RPIQ e baixos valores de RMSE. Os mapas para areia, MO e óxidos de ferro obtidos via krigagem ordinária superaram aqueles obtidos para os mesmos atributos usando modelos de RL baseados em co-variáveis obtidas via SR, e para argila, ambas abordagens atingiram o mesmo nível de acurácia. O mapeamento dos conteúdos de argila, areia, matéria orgânica e óxidos de ferro do solo via modelos de RL múltipla utilizando produtos do Landsat 5 é uma técnica simples e fácil de reproduzir, apropriada para o mapeamento de atributos do solo em áreas de agricultura com solo exposto.
Hu, Ronghai. "Estimation cohérente de l'indice de surface foliaire en utilisant des données terrestres et aéroportées." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD021/document.
Leaf Area Index (LAI), defined as one half of the total leaf area per unit ground surface area, is a key parameter of vegetation structure for modeling Earth's ecological cycle and its acquisition accuracy always has the need and opportunity for improvement. Active laser scanning provides an opportunity for consistent LAI retrieval at multiple scales because terrestrial laser scanning (TLS) and airborne laser scanning (ALS) have the similar physical mechanism. However, the three-dimensional information of laser scanning is not fully explored in current methods and the traditional theories require adaptation. In this thesis, the path length distribution model is proposed to model the clumping effect, and it is applied to the TLS and ALS data. The method of obtaining the path length distribution of different platforms is studied, and the consistent retrieval model is established. This method is found to improve the individual tree measurement in urban areas and LAI mapping in natural forest, and its results at consistent at different scales. The model is expected to facilitate the consistent retrieval of the forest leaf area index using ground and airborne data
Boisier, Juan Pablo. "Évaluer les impacts robustes du changement d'usage des sols sur le climat des 150 dernières années et sur le climat projeté pour le siècle prochain." Phd thesis, Palaiseau, Ecole polytechnique, 2012. https://pastel.hal.science/docs/00/78/79/72/PDF/Manuscrit_final_these_Boisier.pdf.
Land-use change (LUC) is an important climate forcing due to the underlying alterations of the properties of the soil-vegetation system. However, the knowledge of these biogeophysical impacts of LUC is middling, notably due to the large number of processes involved. By means of model intercomparison and other approaches specifically developed, this study aims to identify the robust climate signals of LUC as well as to assess the associated uncertainties. LUC since the preindustrial period has led to extensive deforestation in the northern temperate regions and therefore to increases in surface albedo. The amplitude of this impact and the role of the non-radiative effects in summer are still quite uncertain within the model results. These uncertainties respond (1) to the way LUC is implemented in land surface models (LSMs) and (2) to the intrinsic model sensitivities to LUC. We show that the second point could explain more than 50% of the inter-model dispersion in key variables for the surface climate such as the evapotranspiration. We therefore developed statistical tools to reconstruct the impacts of LUC on the surface albedo and the evapotranspiration using present-day observations and the land-cover maps prescribed in the LSMs here assessed. The analyses carried out here show that current uncertainties in the climate impacts of LUC are in major part the result of the land-surface parameterizations used in climate models and, hence, could be reduced with a more thoroughly evaluation of LSMs
Montagner, Jean-Paul. "Etude de la structure profonde de la terre a partir des ondes de surface de longue periode." Paris 6, 1986. http://www.theses.fr/1986PA066188.
Cotte, Nathalie. "Détermination des variations latérales de la lithosphère par l'analyse des ondes de surface enregistrées par des réseaux régionaux." Phd thesis, Grenoble 1, 2000. http://tel.archives-ouvertes.fr/tel-00703264.
Sy, Souleymane. "Impact du changement d'occupation des sols passé et à venir sur la dynamique de la circulation de la mousson ouest africaine." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066208/document.
By climate models developed in the LUCID project and CMIP5 models used in the LUCID-CMIP5 projet, this thesis aims to identify and evaluate biogeophysical impacts of LULCC of the past 150 years and the end of XXIst century on surface climate in West Africa. Focusing analysis in two contrasted regions of West Africa: Sahel and Guinea where land cover change is above 5% since pre-industrial times, results reveal expansion of crops and pasture and deforestation in Guinea in all LUCID models. In this work, simulations of present-day rainfall and surface air temperature have been compared with observed datasets. Results show that the observed mean and inter-annual variability of rainfall are respectively underestimated and overestimated by most of the seven climate models. Overall surface air temperature is better simulated than precipitation.Two simulations of rainfall and surface air temperature, forced respectively with present-day and pre-industrial land cover distribution are also compared. Results show that there is no obvious/visible difference between the two simulations with respect to mean climatic values of both rainfall and temperature as if the changes in land cover did not really matter for the good representation of those variables. Finally, this thesis evaluates leaf area index (LAI) in the LUCID models and its relationships with surface climate. Observations reveal that precipitation is highly and positively correlated to foliage density with values larger or equal to 0.8 in both the Sahel and Guinea. Five out of seven models show positive correlations, but not as large as in the observations. However none of the models is able to capture a larger correlation between precipitation and LAI in Guinea than in the Sahel. Most of climate models show that correlation between LAI and surface air temperature is positive in the Sahel and negative in Guinea. It suggests that more LAI in Guinea will lead to more evapotranspiration and therefore cooler surface, while in the Sahel the albedo effect of increased LAI may dominate and increase surface temperature. Finally, analysis reveals that historical effects of land-use changes are not regionally significant among the seven climate models due to a small land-cover change prescribed in these regions compared to the changes induced by large scale forcing such as sea surface temperatures changes and CO2 concentration increase.Furthermore, biogeophysical impact of land-use change in the XXIst Century climate were evaluated using specific simulations similar to RCP8.5 scenarios but with a prescribed fixed land cover map on 2006. The analysis reveals, that in contrast of last 150 years, deforestation continues in the coming years in tropical region in scenarios resulting from the extension of the cultivated area reaching 15 million km2 in 2100 over tropical Africa. Regionally, the biogeophysical impacts of projected changes in land cover in RCP8.5 scenarios were generally small but statistically significant in the Sahel and Central Africa regions where deforestation is more than 10% with a wide dispersion of climate response due to differents parameterizations of land surface in climate models
Dari, Jacopo. "Towards a better understanding of the Anthropogenic Impact on the Hydrological Cycle: Detecting and Estimating Irrigation through Remote Sensing Soil Moisture." Doctoral thesis, Universitat Ramon Llull, 2021. http://hdl.handle.net/10803/671502.
El riego es el principal consumo antropogénico de agua dulce. Se prevé que la explotación de los recursos hídricos para mejorar la producción de alimentos mediante prácticas de riego seguirá aumentando en los próximos decenios. De hecho, se prevé que el crecimiento demográfico y los cambios climáticos ejerzan una presión aún mayor sobre los recursos hídricos disponibles. A pesar de que el riego tiene consecuencias directas en la gestión racional de los recursos hídricos, así como en la producción de alimentos, falta un conocimiento detallado de los lugares en los que realmente se riega en todo el mundo y de cuánta agua se utiliza realmente para las prácticas de riego. En esta investigación se han elaborado métodos para detectar y cartografiar las zonas donde realmente se riega, así como métodos para estimar las cantidades de agua que se aplican para el riego; las metodologías propuestas utilizan datos de humedad del suelo provenientes de la teledetección espacial. En esta investigación se han adoptado dos casos de estudio: el primero se sitúa en la cuenca del Ebro, en el noreste de España, mientras que el otro es la cuenca del Alto Tíber, en Italia central. Se han ensayado varios productos de humedad del suelo obtenidos por teledetección con diferentes resoluciones espaciales para evaluar los que mejor funcionan en la detección del riego y, por lo tanto, en la cartografía de las zonas de regadío. Además, se han realizado estimaciones cuantitativas de las cantidades de agua aplicadas para el riego. La actividad de detección y cartografía del riego se ha llevado a cabo en ambos casos de estudio. En el español se ha evaluado inicialmente la capacidad de detección de riego de varios productos de teledetección. Se han evaluado los siguientes conjuntos de datos de humedad del suelo: SMAP (Soil Moisture Active Passive) a 1 km y 9 km, SMOS (Soil Moisture and Ocean Salinity) a 1 km, Sentinel-1 a 1 km, y ASCAT (Advanced SCATterometer) a 12,5 km. Las versiones de 1 km de SMAP y SMOS se obtienen mediante la desagregación con el método DISPATCH (DISaggregation based on Physical And Theoretical scale Change). La detectabilidad del riego por los productos considerados se ha evaluado mediante índices derivados de la teoría de la estabilidad temporal aquí utilizada bajo esta nueva perspectiva. Además, se han elaborado mapas de las zonas irrigadas producidos a través del algoritmo de agrupamiento K-medias. En las zonas agrícolas de la cuenca del Alto Tíber, en Italia, se ha realizado un análisis a doble escala. En el análisis a 1 km de resolución espacial, se ha aplicado el mismo procedimiento adoptado en el caso de estudio de la cuenca del Ebro para evaluar la detectabilidad de la irrigación mediante la humedad del suelo por teledetección. Se han utilizado los siguientes productos: SMAP a 1 km, la versión Sentinel-1 a 1 km entregada por el Copernicus Global Land Service, y una versión Sentinel-1 a escala de parcela (producida por THEIA) agregada a 1 km. Obsérvese que los dos primeros productos son los mismos que también se utilizaron en el caso de estudio español. En este análisis, así como en el realizado sobre el área de estudio en la cuenca del Ebro, se ha utilizado como soporte el modelo de superficie terrestre SURFEX-ISBA (SURface EXternalisée - Interaction Sol Biosphère Atmosphère). En el análisis a escala de parcela, los datos del THEIA Sentinel-1 agregados a 100 m se han utilizado para producir mapas de alta resolución de las zonas de regadío mediante el algoritmo de agrupamiento K-medias. La actividad de cuantificación del riego se ha llevado a cabo en la zona de estudio de la cuenca del Ebro únicamente; se han realizado dos experimentos: uno explotando SMAP con datos a 1 km de resolución y otro explotando SMOS con datos a 1 km. Ambos conjuntos de datos se han utilizado para forzar el algoritmo SM2RAIN adaptado a la estimación del riego. En el algoritmo se ha aplicado una modelización más realista del término de evapotranspiración para reproducir adecuadamente la evapotranspiración de los cultivos según el modelo de la FAO (Organización de las Naciones Unidas para la Agricultura y la Alimentación). Los análisis realizados tienen por objeto colmar las lagunas existentes en el campo de la investigación relacionada con el riego; los resultados obtenidos son útiles para evaluar el impacto de las prácticas de riego en el ciclo hidrológico.
Irrigation is the primary source of anthropogenic freshwater consumptions. The exploitation of water resources to improve the food production through irrigation practices is expected to further increase in the upcoming decades. In fact, the population growth and climate changes are expected to put even more pressure on the available water resources. Despite irrigation having direct implications on the rational management of water resources, as well as on food production, a detailed knowledge of where irrigation actually occurs worldwide and of how much water is actually used for irrigation practices is missing. In this research, approaches to detect and map areas where irrigation actually occurs, as well as methods to estimate the amounts of water applied for irrigation, have been developed; the proposed methodologies exploit remote sensing soil moisture. Two case studies have been considered in this research: the first one is located within the Ebro basin, in North-eastern Spain, while the other one is the Upper Tiber basin, in central Italy. Several remotely sensed soil moisture products at different spatial resolutions have been tested to evaluate the best performing ones in detecting irrigation signals and thus mapping irrigated areas. In addition, quantitative estimates of the water amounts applied for irrigation have been performed. The irrigation detection and mapping activity has been carried out over both case studies. In the Spanish one, the capability to detect irrigation of several remote sensing products has been initially assessed. The following soil moisture data sets have been evaluated: SMAP (Soil Moisture Active Passive) at 1 km and 9 km, SMOS (Soil Moisture and Ocean Salinity) at 1 km, Sentinel-1 at 1 km, and ASCAT (Advanced SCATterometer) at 12.5 km. The 1 km versions of SMAP and SMOS are obtained through downscaling with the DISPATCH (DISaggregation based on Physical And Theoretical scale CHange) method. The detectability of irrigation by the considered products has been assessed through indices derived from the temporal stability theory here used under this new perspective. Furthermore, maps of irrigated areas have been produced through the K-means clustering algorithm. Over the agricultural areas in the Upper Tiber basin, in Italy, a double-scale analysis has been carried out. In the analysis at 1 km spatial resolution, the same procedure adopted over the case study in the Ebro basin to evaluate the detectability of irrigation through remotely sensed soil moisture has been applied. The following products have been used: SMAP at 1 km, the Sentinel-1 at 1 km version delivered by the Copernicus Global Land Service, and a plot-scale-born Sentinel-1 version (produced by THEIA) aggregated at 1 km. Note that the first two products are the same used over the Spanish case study also. In this analysis, as well as in the one carried out over the study area in the Ebro basin, surface soil moisture simulated by the SURFEX-ISBA (SURface EXternalisée - Interaction Sol Biosphère Atmosphère) land surface model has been used as support. In the plot-scale analysis, THEIA Sentinel-1 data aggregated at 100 m have been used to produce high-resolution maps of irrigated areas through the K-means clustering algorithm. The irrigation quantification activity has been carried out over the study area in the Ebro basin only; two experiments have been performed: one exploiting SMAP at 1 km data and another one exploiting SMOS at 1 km data. Both data sets have been used to force the SM2RAIN algorithm adapted to estimate irrigation. A more realistic modeling of the evapotranspiration term has been implemented into the algorithm to properly reproduce the crop evapotranspiration according to the FAO (Food and Agriculture Organization) model. The analyses carried out are aimed at filling the existing gaps in the irrigation-related research field; the obtained results are useful to assess the impact of irrigation practices on the hydrological cycle.
L’irrigazione è la principale fonte di consumo di acqua dolce. Nei prossimi decenni è atteso un ulteriore sfruttamento della risorsa idrica per incrementare la produzione di cibo attraverso le pratiche irrigue. Si stima infatti che la crescita della popolazione e i cambiamenti climatici possano esercitare una pressione ancora maggiore sulle risorse idriche disponibili. Nonostante le importanti implicazioni che ha l’irrigazione sulla gestione razionale dell’acqua e sulla produzione di cibo, non si ha una conoscenza dettagliata di dove l’irrigazione effettivamente avvenga nel mondo e di quanta acqua venga effettivamente utilizzata per le pratiche irrigue. In questa ricerca sono stati sviluppati approcci per rilevare e mappare le aree dove effettivamente si verifica l’irrigazione e per stimare i volumi irrigui; le metodologie proposte sfruttano l’umidità del suolo rilevata da satellite. In questa ricerca sono stati considerati due casi di studio: il primo si trova nel bacino del fiume Ebro, nel Nord-Est della Spagna, mentre l’altro è il bacino superiore del Tevere, nell’Italia centrale. Diversi prodotti di umidità del suolo da satellite, caratterizzati da diverse risoluzioni spaziali, sono stati valutati al fine di determinare i più performanti nel rilevare segnali di irrigazione e quindi mappare le aree irrigate. Inoltre, sono state eseguite stime quantitative dei volumi di acqua utilizzati per pratiche irrigue. L’attività di rilievo e mappatura dell’irrigazione è stata condotta su entrambe le aree pilota. In quella spagnola, è stata valutata la capacità di rilevare l’irrigazione di diversi prodotti di umidità del suolo. Sono stati considerati i seguenti set di dati: SMAP (Soil Moisture Active Passive) a 1 km e 9 km, SMOS (Soil Moisture and Ocean Salinity) a 1 km, Sentinel-1 a 1 km e ASCAT (Advanced SCATterometer) a 12.5 km. Le versioni a 1 km di SMAP e SMOS sono ottenute tramite disaggregazione eseguita con il metodo DISPATCH (DISaggregation based on Physical And Theoretical scale CHange). La capacità di rilevare l’irrigazione da parte dei prodotti considerati è stata valutata tramite indici derivanti dalla teoria della stabilità temporale e usati in questo studio sotto una nuova prospettiva. Inoltre, sono state prodotte delle mappe delle aree irrigate attraverso l’algoritmo di classificazione K-means. Un’analisi a doppia scala spaziale è stata condotta sulle aree agricole all’interno del bacino superiore del Tevere, in Italia. Nell’ambito dell’analisi alla risoluzione spaziale di 1 km, è stata applicata la stessa procedura già adottata per il caso di studio nel bacino dell’Ebro per valutare la possibilità di rilevare l’irrigazione tramite umidità del suolo da satellite. Sono stati utilizzati i seguenti prodotti: SMAP a 1 km, la versione a 1 km di Sentinel-1 fornita da Copernicus Global Land Service e una versione di Sentinel-1 originariamente prodotta de THEIA alla scala di parcella e aggregata a 1 km. Va sottolineato che i primi due prodotti menzionati sono stati utilizzati anche sull’area pilota in Spagna. Sia in questa analisi che in quella condotta nel bacino dell’Ebro, dati di umidità del suolo superficiale modellati tramite il modello di superficie terrestre SURFEX-ISBA (SURface EXternalisée - Interaction Sol Biosphère Atmosphère) sono stati utilizzati come supporto. Nell’analisi alla scala di parcella, sono stati impiegati i dati di Sentinel-1 prodotti da THEIA e aggregati a 100 m al fine di produrre mappe di aree irrigate ad alta risoluzione tramite l’algoritmo di classificazione K-means. L’attività di quantificazione dell’irrigazione è stata finalizzata solamente per l’area pilota nel bacino dell’Ebro; sono stati condotti due esperimenti: uno utilizzando i dati da SMAP a 1 km e un altro sfruttando i dati da SMOS a 1 km. Entrambi i set di dati sono stati utilizzati per forzare la versione dell’algoritmo SM2RAIN adattata per la stima dell’irrigazione. Una modellazione più realistica dell’evapotraspirazione è stata implementata nell’algoritmo al fine di riprodurre adeguatamente l’evapotraspirazione delle colture secondo il modello FAO (Food and Agriculture Organization). Le analisi condotte sono finalizzate a colmare le lacune esistenti nel campo di ricerca relativo all’irrigazione; i risultati ottenuti sono utili per valutare l’impatto delle pratiche irrigue sul ciclo idrologico.
Sy, Souleymane. "Impact du changement d'occupation des sols passé et à venir sur la dynamique de la circulation de la mousson ouest africaine." Electronic Thesis or Diss., Paris 6, 2016. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2016PA066208.pdf.
By climate models developed in the LUCID project and CMIP5 models used in the LUCID-CMIP5 projet, this thesis aims to identify and evaluate biogeophysical impacts of LULCC of the past 150 years and the end of XXIst century on surface climate in West Africa. Focusing analysis in two contrasted regions of West Africa: Sahel and Guinea where land cover change is above 5% since pre-industrial times, results reveal expansion of crops and pasture and deforestation in Guinea in all LUCID models. In this work, simulations of present-day rainfall and surface air temperature have been compared with observed datasets. Results show that the observed mean and inter-annual variability of rainfall are respectively underestimated and overestimated by most of the seven climate models. Overall surface air temperature is better simulated than precipitation.Two simulations of rainfall and surface air temperature, forced respectively with present-day and pre-industrial land cover distribution are also compared. Results show that there is no obvious/visible difference between the two simulations with respect to mean climatic values of both rainfall and temperature as if the changes in land cover did not really matter for the good representation of those variables. Finally, this thesis evaluates leaf area index (LAI) in the LUCID models and its relationships with surface climate. Observations reveal that precipitation is highly and positively correlated to foliage density with values larger or equal to 0.8 in both the Sahel and Guinea. Five out of seven models show positive correlations, but not as large as in the observations. However none of the models is able to capture a larger correlation between precipitation and LAI in Guinea than in the Sahel. Most of climate models show that correlation between LAI and surface air temperature is positive in the Sahel and negative in Guinea. It suggests that more LAI in Guinea will lead to more evapotranspiration and therefore cooler surface, while in the Sahel the albedo effect of increased LAI may dominate and increase surface temperature. Finally, analysis reveals that historical effects of land-use changes are not regionally significant among the seven climate models due to a small land-cover change prescribed in these regions compared to the changes induced by large scale forcing such as sea surface temperatures changes and CO2 concentration increase.Furthermore, biogeophysical impact of land-use change in the XXIst Century climate were evaluated using specific simulations similar to RCP8.5 scenarios but with a prescribed fixed land cover map on 2006. The analysis reveals, that in contrast of last 150 years, deforestation continues in the coming years in tropical region in scenarios resulting from the extension of the cultivated area reaching 15 million km2 in 2100 over tropical Africa. Regionally, the biogeophysical impacts of projected changes in land cover in RCP8.5 scenarios were generally small but statistically significant in the Sahel and Central Africa regions where deforestation is more than 10% with a wide dispersion of climate response due to differents parameterizations of land surface in climate models
Faivre, Robin. "Multi-sensor remote sensing parameterization of heat fluxes over heterogeneous land surfaces." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAD017/document.
The parameterization of heat transfer by remote sensing, and based on SEBS scheme for turbulent heat fluxes retrieval, already proved to be very convenient for estimating evapotranspiration (ET) over homogeneous land surfaces. However, the use of such a method over heterogeneous landscapes (e.g. semi-arid regions or agricultural land) becomes more difficult, since the principle of similarity theory is compromised by the presence of different heat sources with various heights. This thesis aims at first to propose and evaluate some models based on vegetation geometry for retrieving the surface roughness length for momentum transfer (z0m), which is a key parameter in the characterization of heat transfer. Such an investigation can only be led at a small scale with very-high resolution remote sensing data, for a precise description of the land surface. Therefore, the second aspect of this work is to determine how to address the characterization of heat transfer for regional studies. Then, the reliability of SEBS for estimating turbulent heat fluxes at large spatial and temporal scales has been evaluated. To do so, the Multi-Scale SEBS approach (MSSEBS) has been implemented for a 2.4 million km2 area including the Tibetan Plateau and the headwaters of the major rivers of East and South Asia. The addition of gap-filled hourly FY-2 LST data to advanced daily averaged net radiation and land surface parameters, allows to compute time-series of land surface ET over the Tibetan Plateau during the period 2008-2010, and on a daily basis
Chouinard, Christian. "Reconstitutions des températures de surface au Canada : des températures basales du glacier laurentidien aux changements récents du climat arctique." Thèse, 2008. http://www.archipel.uqam.ca/876/1/D1648.pdf.
Baptista, Bruno Baeta Magalhaes. "Modelação 3D da Barragem do Cabril por Varrimento LASER Terrestre e Fotogrametria Digital." Master's thesis, 2017. http://hdl.handle.net/10316/83119.
Several large concrete dams began to be built in the first half of the last century. Many of these structures are now over than 50 years old and the security control of these structures becomes fundamental. This control is fundamental for the maintenance of the structure and to understand these infrastructures behaviour. Security control requires monitoring programs in accordance with the types of structures. The visual inspection is an added advantage, considering that in many old structures there are no installed equipment’s to monitor their behaviour. With the development of LASER technologies, such as the Combined Terrestrial Imaging System (CTIS), it is expected a new mode of visual inspection, called visual assisted inspections. On reflective surfaces the Terrestrial Laser Scanner (TLS) gets the coordinates of millions of points used to model 3D objects in a fast and precise way. By attaching a digital camera to the laser scanner, it is also possible to integrate the laser data with the digital images. After processing the data from the CTIS, orthoimages with adequate resolution are acquired and are useful for the identification and classification of anomalies as well as, for the analysis of structure deformations. With three-dimensional models obtained at different epoch, with different water level and different environmental conditions, it is possible to quantify the deformations of the dam. This report describes the study of the application of the CTIS in the Cabril dam in the two mentioned aspects, the processing of orthoimages and the evaluation of the three dimensional models. In the structure of this report there are included two papers of the two mentioned aspects that were presented at the “VIII Conferência Nacional de Cartografia e Geodesia” that took place between 29th and 30th of October of 2015 in Lisbon.
As grandes barragens de betão começaram a ser construídas na primeira metade do século passado. Muitas dessas estruturas têm agora mais de 50 anos e, devido ao seu envelhecimento, torna-se fundamental o controlo de segurança dessas estruturas. Estender a vida útil destas infraestruturas é também uma necessidade de rentabilização que passa igualmente pelo referido controlo. O controlo de segurança requer programas de monitorização adequados aos tipos de estruturas. A inspecção visual é uma vantagem acrescida, tendo em conta que em muitas estruturas antigas não existem equipamentos instalados para a monitorização do seu comportamento. Com o avanço das tecnologias LASER, como é o caso do Sistema Combinado de Imagens Terrestre (Combined Terrestrial Imagin System, CTIS), perspectiva-se um novo modo de inspecções visuais, designadas por inspecções visuais assistidas. Os Laser Scanner Terrestres (Terrestrial Laser scanner, TLS) determinam as coordenadas de milhões de pontos em superfícies reflectivas, obtendo-se assim modelos tridimensionais dos objectos de uma maneira rápida e precisa. Acoplando ao laser scanner uma câmara digital, é possível integrar a informação laser com as imagens digitais. Após processamento adequado, obtêm-se orto-imagens com a resolução adequada, úteis para a identificação e classificação de anomalias bem como para análise de deformações da estrutura. Com os modelos tridimensionais obtidos em diferentes épocas, com cotas de albufeira e condições meteorológicas diferentes, é possível quantificar as deformações do paramento da barragem. Este relatório descreve o estudo da aplicação dos Sistemas Combinados de Imagens Terrestres à Barragem do Cabril nas duas vertentes referidas, a aquisição de orto-imagens e a comparação de diferentes modelos tridimensionais. Na estrutura deste relatório, estão na íntegra os dois artigos referentes às duas vertentes referidas, que foram apresentados na VIII Conferência Nacional de Cartografia e Geodesia que decorreu entre 29 e 30 de Outubro de 2015, em Lisboa.
Johannsen, João Frederico Gonçalves. "Evaluation of land surface temperature in atmospheric reanalyses using Earth observations." Master's thesis, 2019. http://hdl.handle.net/10451/39566.
A temperatura da superfície terrestre (SKT) é um dos parâmetros-chave nas trocas terra-atmosfera de energia e água. Além disso, é cada vez mais importante na assimilação de dados e na parametrização de variáveis em modelos. Estudos anteriores apontam para subestimações consideráveis da SKT em reanálises, principalmente durante o dia e em regiões semi-áridas e áridas. Na primeira parte desta tese, a SKT de duas reanálises (ERA-Interim e ERA5) do Centro Europeu de Previsão de Tempo a Médio-Prazo (ECMWF) é avaliada, tendo como produto de referência a temperatura da superfície terrestre (LST) obtida por satélite pelos Serviços de Aplicações de Satélite a Análises da Superfície Terrestre (LSA-SAF). De igual forma, é avaliada a SKT de simulações offline de uma versão do modelo HTESSEL do ECMWF muito semelhante à utilizada na concepção da ERA5. Este estudo é realizado entre 2004 e 2015 (período em que a LST reprocessada se encontra disponível) sobre a Península Ibérica, numa resolução espacial de 0.25º × 0.25º. Como a LST de satélite tem uma resolução maior (~5 km), é realizado o upscaling dos dados de satélite para se poder fazer a comparação com as reanálises. Além disso, esta base de dados realiza medições num determinado pixel apenas quando não há nuvens sobre esse pixel. Por causa disso, aplica-se um limite máximo de cobertura nebulosa de 0.3 em cada pixel e para cada produto, de forma a evitar uma contaminação elevada dos dados por nuvens e, ao mesmo tempo, manter uma percentagem considerável de dados válidos. Quatro métricas de desempenho são aplicadas à SKT máxima e mínima diária: erro médio, desvio-padrão do erro, correlação temporal e a raiz quadrada do erro médio quadrático. Para facilitar a organização dos resultados, aplica-se o algoritmo K-Means de forma a dividir o domínio em diferentes clusters. Os clusters são determinados a partir do ciclo diurno médio da LST no Verão dos doze anos considerados no estudo. Os resultados mostram, em todos os produtos, uma subestimação considerável da SKT de dia e uma sobrestimação pouco significativa de noite, em linha com estudos anteriores, sendo essa disparidade superior em regiões mais áridas. No geral, a ERA5 apresenta um produto com qualidade superior em relação à ERA-Interim, pois é a reanálise que mais se aproxima das observações de satélite. Mostra-se também que existe uma correlação razoavelmente elevada entre o erro na representação da cobertura vegetal no modelo (ao comparar a fracção de cobertura vegetal do modelo pela observada pela base de dados da Copernicus) e o erro médio na simulação da SKT. Na segunda parte deste trabalho, são aplicadas mudanças a alguns parâmetros do modelo HTESSEL e o seu impacto na simulação da SKT é avaliado pelas observações de satélite da LST, num domínio mais restrito centrado em Évora (quatro pontos na resolução original de 0.25º × 0.25º). A implementação de uma representação mais realista de coberto vegetal no modelo é obtida a partir da base de dados de cobertura terrestre da ESA-CCI, mantendo os tipos de vegetação alta/baixa originais considerados pelo modelo mas alterando a respectiva fracção de cobertura vegetal. O domínio passa a ser coberto maioritariamente por vegetação baixa, ao contrário do domínio original que era coberto quase na totalidade por vegetação alta. Esta nova representação da vegetação tem um impacto positivo na SKT durante o dia, e uma nova discretização do solo (nove camadas em vez de quatro) reduz ainda mais o erro, embora com um impacto menos acentuado do que a introdução da nova vegetação. Ainda assim, mesmo depois destas alterações, o viés nocturno e a diferença de fase durante o dia mantêm-se no ciclo diurno médio da SKT. É importante referir que o tipo de vegetação baixa considerado pelo modelo HTESSEL não é directamente equivalente ao obtido com os dados da ESA-CCI e ao utilizar outros tipos de vegetação baixa no modelo, estes originam resultados menos positivos. Isto dever-se-á ao facto da cobertura vegetal ser menor no tipo de vegetação baixa originalmente considerado pelo modelo quando comparado com os restantes tipos existentes, o que implica um aumento da fracção de cobertura vegetal e, consequentemente, um aumento do viés da SKT quando se muda para outro tipo de vegetação baixa. Finalmente, um estudo de sensibilidade é aplicado ao pârametro cveg, que representa a cobertura vegetal do modelo, de forma a verificar a sua relação com o viés na simulação da SKT, utilizando a representação de vegetação original do modelo HTESSEL e, seguidamente, a representação revista. O parâmetro cveg é perturbado com valores entre 0.1 e 1, para os tipos de vegetação alta e baixa, formando no total 100 pares de cveg. Esses pares são obtidos através de uma distribuição quasi-aleatória, distribuição de Sobol, que permite preencher na totalidade o domínio considerado, sem introduzir correlações entre as diferentes perturbações e sem criar clusters e espaços vazios no domínio. Este estudo reafirma a importância da representação da vegetação no modelo, pois existe uma correlação entre cveg e o viés da SKT máxima diária quando se considera a vegetação revista (ao contrário do que acontece com a vegetação original do modelo, em que não se verifica qualquer correlação com o erro). As simulações desacopladas (offline) permitem avaliar o impacto dos parâmetros de superfície na simulação de SKT, mas é igualmente importante estudar o efeito da vegetação revista em simulação acopladas com a atmosfera. Também é importante referir que as mudanças na cobertura de vegetação afectam o balanço de água (que não é estudado neste trabalho) e causam outras alterações noutras estações do ano. Contudo, a pouca disponibilidade de dados de LST de satélite e de outras observações (como, por exemplo, fluxos e temperatura e humidade do solo) dificultam eventuais estudos adicionais. Ainda que a ERA5 demonstre ser um produto com melhor qualidade que a ERA-Interim, os resultados sugerem a necessidade de uma revisão da vegetação no modelo HTESSEL sobre a Península Ibérica, nomeadamente as fracções de cobertura de vegetação baixa / alta. Do mesmo modo, a própria definição dos tipos de vegetação baixa / alta e o valor de cveg associado poderão também precisar de uma revisão.
The surface skin temperature (SKT) is a key variable in surface-atmosphere energy and water exchanges. In the first part of this work, the SKT from two reanalyses (ERA-Interim and ERA5) of the European Centre for Medium-Range Weather Forecasts (ECMWF) is evaluated against satellite-based Land Surface Temperature (LST) retrieved by the Satellite Application Facility on Land Surface Analysis (LSA-SAF), during the 2004-2015 period over the Iberian Peninsula. Offline simulations by the Hydrology Tiled ECMWF Scheme of Surface Exchanges over Land (HTESSEL) model are also assessed. We apply four performance metrics to the daily maximum and minimum SKT: the mean error, standard deviation of the error, temporal correlation and root mean squared error. The results show an underestimation of the daytime SKT and a small overestimation of nighttime SKT in all the products, which is in line with previous studies. In general, ERA5 presents a consistent improvement over ERA-Interim by showing an overall better agreement with the satellite observations. There is also a reasonably high correlation between the misrepresentation of vegetation cover in the HTESSEL model and the daily maximum SKT bias. In the second part of the thesis, we apply changes to some parameters of the HTESSEL model. The parameters’ impact in the simulation of SKT is then assessed by comparing them to the satellite-LST in a confined domain centred in Évora. The implementation of a revised model representation of vegetation cover (based on the ESA-CCI Land Cover Dataset) is shown to have a positive impact on SKT, especially during daytime. A new soil discretization scheme, on the other hand, does not significantly impact the simulation of SKT. Finally, a sensitivity study applied to the cveg parameter (the model vegetation cover) reaffirms the importance of the representation of vegetation in the model, as there is a correlation between cveg and the daily maximum SKT bias with the revised model vegetation (while the same correlation cannot be reproduced with the original model vegetation).