• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 23
  • 11
  • 10
  • 3
  • 1
  • 1
  • Tagged with
  • 51
  • 51
  • 24
  • 22
  • 19
  • 13
  • 12
  • 12
  • 12
  • 11
  • 9
  • 8
  • 7
  • 7
  • 7
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

The K-distribution method for calculating thermal infrared radiative transfer in the atmosphere : A two-stage numerical procedure based on Gauss-Legendre quadrature

Nerman, Karl January 2022 (has links)
The K-distribution method is a fast approximative method used for calculating thermal infrared radiative transfer in the atmosphere, as opposed to the traditional Line-by-line method, which is precise, but very time-costly. Here we consider the atmosphere to consist of homogeneous and plane-parallel layers in local thermal equilibrium. This lets us use efficient upwards recursion for calculating the thermal infrared radiative transfer and ultimately the outgoing irradiance at the top of the atmosphere. Our specific implementation of the K-distribution method revolves around changing the integration space from the wavenumber domain to the g domain by employing Gauss-Legendre quadrature in two steps. The method is implemented in MATLAB and is shown to be several thousand times faster than the traditional Line-by-line method, with the relative error being only 3 % for the outgoing irradiance at the top of the atmosphere.
42

The effects of magmatic evolution,  crystallinity, and microtexture on the visible/near-infrared and  thermal-infrared spectra of volcanic rocks

Noel A Scudder (16649295) 01 August 2023 (has links)
<p>The natural chemical and physical variations that occur within volcanic rocks (petrology) provide critical insights into mantle and crust conditions on terrestrial bodies. Visible/near-infrared (VNIR; 0.3-2.5 µm) and thermal infrared (TIR; 5-50 µm) spectroscopy are the main tools available to remotely characterize these materials from satellites in orbit. However, the accuracy of petrologic information that can be gained from spectra when rocks exhibit complex variations in mineralogy, crystallinity, microtexture, and oxidation state occurring together in natural settings is not well constrained. Here, we compare the spectra of a suite of volcanic planetary analog rocks from the Three Sisters, OR to their mineralogy, chemistry, and microtexture from X-ray diffraction, X-ray fluorescence, and electron microprobe analysis. Our results indicate that TIR spectroscopy is an effective petrologic tool in such rocks for modeling bulk mineralogy, crystallinity, and mineral chemistry. Given a library with appropriate glass endmembers, TIR modeling can derive glass abundance with similar accuracy as other major mineral groups and provide first-order estimates of glass wt.% SiO2 in glass-rich samples, but cannot effectively detect variations in microtexture and minor oxide minerals. In contrast, VNIR spectra often yield non-unique mineralogic interpretations due to overlapping absorption bands from olivine, glass, and Fe-bearing plagioclase. In addition, we find that sub-micron oxides hosted in transparent matrix material that are common in fine-grained extrusive rocks can lower albedo and partially to fully suppress mafic absorption bands, leading to very different VNIR spectra in rocks with the same mineralogy and chemistry. Mineralogical interpretations from VNIR spectra should not be treated as rigorous petrologic indicators, but can supplement TIR-based petrology by providing unique constraints on oxide minerals, microtexture, and alteration processes.</p>
43

Désagrégation spatiale de températures Météosat par une méthode d'assimilation de données (lisseur particulaire) dans un modèle de surface continentale / Spatial downscaling of Meteosat temperatures based on a data assimilation approach (Particle Smoother) to constrain a land surface model

Mechri, Rihab 04 December 2014 (has links)
La température des surfaces continentales (LST) est une variable météorologiquetrès importante car elle permet l’accès aux bilans d’énergie et d’eau ducontinuum Biosphère-Atmosphère. Sa haute variabilité spatio-temporelle nécessite desmesures à haute résolution spatiale (HRS) et temporelle (HRT) pour suivre au mieuxles états hydriques du sol et des végétations.La télédétection infrarouge thermique (IRT) permet d’estimer la LST à différentesrésolutions spatio-temporelles. Toutefois, les mesures les plus fréquentes sont souventà basse résolution spatiale (BRS). Il faut donc développer des méthodes pour estimerla LST à HRS à partir des mesures IRT à BRS/HRT. Cette solution est connue sous lenom de désagrégation et fait l’objet de cette thèse.Ainsi, une nouvelle approche de désagrégation basée sur l’assimilation de données(AD) est proposée. Il s’agit de contraindre la dynamique des LSTs HRS/HRT simuléespar un modèle en minimisant l’écart entre les LST agrégées et les données IRT àBRS/HRT, sous l’hypothèse d’homogénéité de la LST par type d’occupation des sols àl’échelle du pixel BRS. La méthode d’AD choisie est un lisseur particulaire qui a étéimplémenté dans le modèle de surface SETHYS (Suivi de l’Etat Hydrique du Sol).L’approche a été évaluée dans une première étape sur des données synthétiques etvalidée ensuite sur des données réelles de télédétection sur une petite région au Sud-Est de la France. Des séries de températures Météosat à 5 km de résolution spatialeont été désagrégées à 90m et validées sur une journée à l’aide de données ASTER.Les résultats encourageants nous ont conduit à élargir la région d’étude et la périoded’assimilation à sept mois. La désagrégation des produits Météosat a été validée quantitativementà 1km à l’aide de données MODIS et qualitativement à 30m à l’aide dedonnées Landsat7. Les résultats montrent de bonnes performances avec des erreursinférieures à 2.5K sur les températures désagrégées à 1km. / Land surface temperature (LST) is one of the most important meteorologicalvariables giving access to water and energy budgets governing the Biosphere-Atmosphere continuum. To better monitor vegetation and energy states, we need hightemporal and spatial resolution measures of LST because its high variability in spaceand time.Despite the growing availability of Thermal Infra-Red (TIR) remote sensing LSTproducts, at different spatial and temporal resolutions, both high spatial resolution(HSR) and high temporal resolution (HTR) TIR data is still not possible because ofsatellite resolutions trade-off : the most frequent LST products being low spatial resolution(LSR) ones.It is therefore necessary to develop methods to estimate HSR/HTR LST from availableTIR LSR/HTR ones. This solution is known as "downscaling" and the presentthesis proposes a new approach for downscaling LST based on Data Assimilation (DA)methods. The basic idea is to constrain HSR/HTR LST dynamics, simulated by a dynamicalmodel, through the minimization of their respective aggregated LSTs discrepancytoward LSR observations, assuming that LST is homogeneous at the land cover typescale inside the LSR pixel.Our method uses a particle smoother DA method implemented in a land surfacemodel : SETHYS model (Suivie de l’Etat Hydrique de Sol). The proposed approach hasbeen firstly evaluated in a synthetic framework then validated using actual TIR LSTover a small area in South-East of France. Meteosat LST time series were downscaledfrom 5km to 90m and validated with ASTER HSR LST over one day. The encouragingresults conducted us to expand the study area and consider a larger assimilation periodof seven months. The downscaled Meteosat LSTs were quantitatively validated at1km of spatial resolution (SR) with MODIS data and qualitatively at 30m of SR withLandsat7 data. The results demonstrated good performances with downscaling errorsless than 2.5K at MODIS scale (1km of SR).
44

Emissividade dos atributos do solo via sensores terrestres e de satélite / Emissivity of soil attributes via terrestrial and satellite sensors

Urbina Salazar, Diego Fernando 05 February 2019 (has links)
A textura e o conteúdo do carbono orgânico (CO) influenciam na resposta espectral dos solos. O estudo desses atributos é de grande importância para a preservação e o manejo adequado da terra na busca de uma agricultura sustentável. O uso de sensores de laboratório e satélites tem se mostrado como uma ferramenta no auxílio para o estudo destes, porém a análise dos atributos do solo com esses sensores tem focado principalmente nas regiões do espectro eletromagnético do visível (Vis), infravermelho próximo (NIR) e infravermelho de ondas curtas (SWIR), com poucos estudos no infravermelho médio (MIR). O objetivo deste trabalho foi identificar o padrão espectral do solo com diferentes granulometrias (areia e argila) e teores de CO utilizando sensores de laboratório e satélite na região do MIR, especificamente na faixa do infravermelho termal (TIR). O estudo teve uma avaliação qualitativa e quantitativa da argila, CO e das frações de areia (fina e grossa). A área de estudo está localizada na região de Piracicaba, São Paulo, Brasil. Foram coletadas 150 amostras de solo a uma profundidade de 0-20 cm. A textura do solo foi determinada pelo método da pipeta e a porcentagem de CO via combustão seca. Dados espectrais em refletância e emissividade (&epsilon;) foram adquiridos com o sensor Fourier Transform Infrared (FT-IR) Alpha (Bruker optics Corporation). Uma imagem \"ASTER_05\" foi adquirida em 15 de julho de 2017 em valores de &epsilon;. As amostras foram separadas por classes texturais e o comportamento espectral no TIR foi descrito. Os dados obtidos pelo sensor de laboratório foram reamostrados para as bandas do sensor de satélite. O comportamento entre os espectros de ambos sensores foi semelhante e teve correlação significativa com os atributos estudados, principalmente para areia. Para os modelos de regressão por mínimos quadrados parciais (PLSR), foram utilizadas seis estratégias (MIR, MIR_ASTER, ASTER, Termal, Termal IDC e MIR IDC) que consistiram no uso de todas as bandas de sensores, ou pela seleção das mesmas que apresentaram as correlações mais significativas com cada um dos atributos. Os modelos apresentaram um bom desempenho na predição de todos os atributos usando o MIR inteiro. No TIR, o modelo para areia total e para as frações fina e grossa foi bom. No caso dos modelos criados com os dados do sensor ASTER, não foram tão promissores quanto os de laboratório. O uso de bandas específicas ajudou a estimar alguns atributos no MIR e no TIR, aumentando o desempenho preditivo melhorando a validação dos modelos. Portanto, a discriminação dos atributos do solo com sensores de satélite pode ser melhorada com a identificação de bandas específicas, como observado nos resultados com sensores de laboratório. / Soil texture and organic carbon (OC) content influence its spectral response. The study of these attributes is relevant for the preservation and proper management of land in pursuit of a sustainable agriculture. Laboratory and satellite sensors have been applied as a useful tool for studying soil attributes, but their analysis with these sensors has mainly focused on the visible (Vis), near infrared (NIR) and shortwave infrared (SWIR) regions of the electromagnetic spectrum, with few studies in the Medium Infrared (MIR). The objective of this study was to identify the spectral pattern of soils with different granulometry (sand and clay) and OC content using laboratory and satellite sensors in the MIR region, specifically in the Thermal Infrared (TIR) range. This study had qualitative and quantitative analyses of clay, OC and sand fractions (fine and coarse). The study area is located in the region of Piracicaba, São Paulo, Brazil. 150 soil samples were collected at a depth of 0-20 cm. Soil texture was determined by the pipette method and the percentage of OC via dry combustion. Reflectance and emissivity (&epsilon;) spectral data were obtained with the Fourier Transform Infrared (FT-IR) Alpha sensor (Bruker Optics Corporation). An image \"ASTER_05\" from July 15, 2017 was acquired with values of &epsilon;. Samples were separated by textural classes and the spectral behavior in the TIR region was described. The data obtained by the laboratory sensor were resampled to the satellite sensor bands. The behavior between spectra of both sensors was similar and had significant correlation with the studied attributes, mainly sand. For the partial least squares regression (PLSR) models, six strategies were used (MIR, MIR_ASTER, ASTER, Thermal, Thermal IDC and MIR IDC), which consisted in the use of all sensors bands, or by the selection of bands that presented the most significant correlations with each one of the attributes. Models presented a good performance in the prediction of all attributes using the whole MIR. In the TIR, models for total sand content and for fine and coarse fractions were good. In the case of models created with ASTER sensor data, they were not as promising as those with laboratory data. The use of specific bands was useful in estimating some attributes in the MIR and TIR, improving the predictive performance and validation of models. Therefore, the discrimination of soil attributes with satellite sensors can be improved with the identification of specific bands, as observed in the results with laboratory sensors.
45

Upscaling of Lacustrine Groundwater Discharge by Fiber Optic Distributed Temperature Sensing and Thermal Infrared imaging

Marruedo Arricibita, Amaya Irene 29 August 2018 (has links)
Der Zustrom von Grundwasser zu Seen (lacustrine groundwater discharge, LGD) kann signifikante Auswirkungen auf Qualität und Quantität des Seewassers haben. Viele Ansätze zur Identifikation und Quantifizierung von LGD basieren auf Temperaturunterschieden zwischen Grund- und Seewasser und der Messung des damit einhergehenden Wärmetransports. Ziel der Doktorarbeit ist es, Signalfortpflanzung und -ausbreitung des Grundwasserzustroms von der Punktskala an der Sediment-Wasser-Grenzfläche über den Wasserkörper bis zur Grenzfläche Wasseroberfläche-Atmosphäre zu untersuchen. Getestet wird die Hypothese, dass das im Verhältnis zum Umgebungswasser wärmere und daher leichtere Grundwasser in der kalten Wassersäule aufsteigt und die Detektion von LGD an der Wasseroberfläche mit thermalen Infrarot Aufnahmen (TIR) erlaubt. Zunächst wird mit der hierarchical patch dynamics ein Konzept entwickelt, das eine angemessene Kombination multipler Techniken zur Erfassung von Wärme- und Wasserflüssen anbietet (Kap. 2). Dabei werden verschiedene räumliche Skalen und ökohydrologische Grenzflächen abgedeckt. Darauf basierend werden in einem Mesokosmos-Experiment unterschiedliche LGD-Raten durch den Zustrom von warmem Wasser am Grund eines Outdoor-Pools simuliert (Kap. 3 und 4). Ein Glasfaserkabel (fibre-optic distributed temperature sensing, FO-DTS) wird in verschiedenen Tiefen installiert, um das Wärmesignal des Grundwasserzustroms unter verschiedenen Bedingungen zu verfolgen. Mit einer TIR-Kamera wird die Temperatur des Oberflächenwassers aufgezeichnet. Die Aufnahmen werden mit FO-DTS-Temperaturen von 2 cm unter der Wasseroberfläche validiert. Die Anwendung von TIR und FO-DTS ermöglicht die Detektion von LGD in der Wassersäule und an der Grenzfläche Wasseroberfläche-Atmosphäre. Wolkenbedeckung und der Tagesgang der Netto-Strahlung kontrollieren den Auftrieb von LGD und die Zuverlässigkeit der TIR-Ergebnisse. Die besten Ergebnisse werden bei Bewölkung und nachts erzielt. / Lacustrine groundwater discharge (LGD) can have significant impacts on lake water quantity and quality. There is a need to understand LGD mechanisms and to improve measurement methods for LGD. Approaches to identify and quantify LGD are based on significant temperature differences between GW and lake water. The main goal of this PhD thesis is to trace heat signal propagation of LGD from the point scale at the sediment-water interface across the overlying water body to the water surface-atmosphere interface. The PhD thesis tests the hypothesis that the positive buoyancy of warm GW causes upwelling across the cold water column and allows detection of LGD at the water surface by thermal infrared imaging (TIR). First, a general conceptual framework is developed based on hierarchical patch dynamics (HPD). It guides researchers on adequately combining multiple heat tracing techniques to identify and quantify heat and water exchange over several spatial scales and ecohydrological interfaces (Chapter 2). Second, the conceptual framework is used for the design of a mesocosm experiment (Chapters 3 and 4). Different LGD rates were simulated by injecting relatively warm water at the bottom of an outdoor mesocosm. A fiber optic distributed temperature sensing (FO-DTS) cable was installed in a 3D setup in the water column to trace the heat signal of the simulated LGD under different weather conditions and over entire diurnal cycles. Finally, a TIR camera was mounted 4 meters above the mesocosm to monitor water surface temperatures. TIR images were validated using FO-DTS temperature data 2 cm below the water surface (Chapter 4). The positive buoyancy of relatively warm LGD allows the detection of GW across the water column and at the water surface-atmosphere interface by FO-DTS and TIR. Cloud cover and diurnal cycle of net radiation strongly control the upwelling of simulated LGD and the reliability of TIR for detection of LGD at the water surface-atmosphere interface. Optimal results are obtained under overcast conditions and during night.
46

Locating Zones and Quantify the Submarine Groundwater Discharge into the Eastern Shores of the Dead Sea-Jordan / Locating Zones and Quantify the Submarine Groundwater Discharge into the Eastern Shores of the Dead Sea-Jordan / Locating Zones and Quantify the Submarine Groundwater Discharge into the Eastern Shores of the Dead Sea-Jordan

Akawwi, Emad Jalal 31 July 2006 (has links)
No description available.
47

Trajectoire temporelle et monitoring hydro-morphologique d'une anastomose rhénane restaurée : le Bauerngrundwasser dans l'île du Rohrschollen (Strasbourg, France) / Temporal trajectory and hydromorphological monitoring of a restored Rhine anastomosis : the Bauerngrundwasser in the Rohrschollen Island (Strasbourg, France)

Eschbach, David 25 September 2017 (has links)
Ce travail s’inscrit dans le cadre d’un projet LIFE+ qui vise à restaurer le fonctionnement hydromorphologique d’un hydrosystème rhénan. Une étude planimétrique couplée à des analyses hydromorphologiques et sédimentologiques ont permis (i) d’améliorer la compréhension des dynamiques d’ajustement passées et (ii) d’identifier les principales limites du projet. Les évolutions morphologiques post-restauration ont été suivies à l’aide d’une combinaison de méthodes géodésiques et géomorphologiques afin de déterminer précisément les volumes déposés / exportés à différentes échelles spatio-temporelles. Enfin, la thermographie infra-rouge aéroportée a permis de mettre en évidence les liens entre la répartition spatiale des anomalies thermiques, les caractéristiques morphodynamiques et les héritages géomorphologiques. L’approche interdisciplinaire développée dans ce travail a permis de guider les choix opérationnels pour optimiser le suivi et l’évaluation des restaurations fonctionnelles futures. / This study is part of a LIFE+ project which aims to restore hydromorphological functioning of a Rhine hydrosystem. A planimetric study combined with hydromorphological and sedimentological analysis allowed to (i) improve understanding of past adjustment dynamics and (ii) identify main limitations of the project. Post-restoration morphological changes were monitored by geodesic and geomorphological methods combination in order to determine accurate volumes of sediment deposited / exported at different spatio-temporal scales. Finally, airborne thermal-infrared was used to highlight the relationship between spatial distribution of thermal anomalies, morphodynamic characteristics and inherited geomorphological features. Interdisciplinary approach leaded in this study was able to guide decision-makers choices in order to optimise the monitoring and assess future functional restorations.
48

Suivi de la température de surface dans les zones de pergélisol arctique par l'utilisation de données de télédétection inversées dans le schéma de surface du modèle climatique canadien (CLASS)

Marchand, Nicolas January 2017 (has links)
Les régions de haute latitude sont actuellement les plus sensibles aux effets du réchauffement climatique, et avec des élévations de température pouvant atteindre les 3 à 8 ◦C au niveau du pôle sur les 100 prochaines années. Les pergélisols (sols présentant des températures négatives deux années consécutives) sont présents sur 25 % des terres émergées de l’hémisphère nord et contiennent de grandes quantités de carbone « gelé », estimées à 1400 Gt (40 % de la quantité de carbone terrestre global). Des études récentes ont montré qu’une partie non négligeable (50 %) des premiers mètres des pergélisols pourraient fondre d’ici 2050, et 90 % d’ici 2100. Le but de l’étude est donc d’améliorer les moyens de suivi de l’évolution des températures du sol dans les zones arctiques, et plus particulièrement dans les régions couvertes de neige. L’objectif est de décrire la température du sol tout au long de l’année y compris sous un manteau neigeux, et d’analyser l’évolution de l’épaisseur de la couche active des pergélisols en relation avec la variabilité du climat. Nous utilisons des données satellites (fusion de données de température dans l’infra-rouge thermique “LST” et de température de brillance micro-onde AMSR-E « Tb ») assimilées dans le schéma de surface du modèle climatique canadien (CLASS, V 3.6) couplé à un modèle simple de transfert radiatif (HUT). Cette approche bénéficie des avantages de chaque type de donnée de manière à réaliser deux objectifs spécifiques : 1-construire une méthodologie solide permettant de retrouver les températures du sol, avec et sans neige, en zone de toundra, et 2-à partir de ces températures du sol, dériver la durée de fonte estivale et l’épaisseur de la couche active du pergélisol. Nous décrivons le couplage des modèles ainsi que la méthodologie permettant l’ajustement des paramètres météorologiques d’entrée du modèle CLASS (essentiellement les températures de l’air et les précipitations issues de la base de données des réanalyses météorologiques NARR) de manière à minimiser les LST et Tb simulées en comparaison aux mesures satellites. Par rapport aux données de mesures de sol de stations météorologiques prises comme référence pour validation dans les zones de toundra d’Amérique du Nord, les résultats montrent que la méthode proposée améliore significativement la simulation des températures du sol lorsqu’on utilise les données LST MODIS et Tb à 10 et 19 GHz pour contraindre le modèle, en comparaison avec les sorties du modèle sans les données satellites. Dans ce processus d’inversion, la correction de l’évolution des conditions de neige au cours de l’hiver contrainte avec le rapport de polarisation à 11 GHz constitue une approche originale. Une analyse de l’erreur pour 4 sites de toundra et sur plusieurs années (18 cas) est effectuée pour la période estivale (1,7 -3,6 K) ainsi que pour la période hivernale couverte de neige (1,8 -3,5 K). L’indice des degrés-jours de fontes annuel, dérivé des températures du sol simulés par notre approche, permet de cartographier les zones de pergélisols continu en accord avec les cartes actuelles. Un meilleur suivi des processus d’évolution des pergélisols, et tout particulièrement de l’impact de la couverture de neige, devrait permettre une meilleure compréhension des effets du réchauffement climatique sur la fonte des pergélisols et l’avenir de leurs stocks de carbone. / Abstract : High latitude areas currently are the most sensitive to global warming effects. In the next 100 years, temperature could rise up to 3 to 8 ◦C at the North Pole. Permafrost (ground with negative temperatures two years in a row) represents 25% of northern hemisphere lands, and contains huge quantities of "frozen" carbon estimated at 1400 Gt (40 % of the global terrestrial carbon). Recent studies showed that a part (50 %) of the permafrost first few meters could melt by 2050, and 90 % by 2100. The goal of our study is to improve our understanding of ground temperature evolution in arctic areas, especially in snow covered regions. The objective is to discribe the ground temperature all year long with and without a snow cover, and to analyze the evolution of the permafrost’s active layer in relation with the climate variability. We use remote sensing data (fuzzed of MODIS "LST" surface temperatures and AMSR-E "Tb" brightness temperatures) assimilated in the canadian landscape surface scheme (CLASS) coupled to a simple radiative transfer model (HUT). This approach takes into account the advantages of each kind of data in order to achieve two objectives : 1 - build a solid methodology allowing to retrieve ground temperatures, with and without a snow cover, in tundra areas ; 2 - from those retrieved ground temperatures, derive the summer melting duration which can be linked to the permafrost active layer thickness. We describe the models coupling as well as the methodology allowing the adjustement of CLASS input meteorological parameters (essentially the air temperatures and precipitations from the NARR meteorological data base) in order to minimize the simulated LST and Tb in comparison to remote sensing data. By using meteorological station’s ground temperature measurments as a reference for validation in North America tundra areas, results show that the proposed method improves the simulation of ground temperatures when using LST MODIS and Tb at 10 and 19 GHz data to constrain the model, in comparison with model outputs without satellite data. Using the Tb polarization ratio H/V at 10 GHz allows an improvement of the constrain on winter period simulations. An analyze of the error is conducted for summer (1,7 - 3,6 K) and winter (1,8 - 3,5 K). We present climatic applications for future work that meets the second objective of the Ph.D. A better understanding of evolution processes of permafrost, and particularly of the impact of the snow cover, should allow us a better understanding of global warming effects on the permafrost’s melting and the future of their carbon stocks.
49

New Approaches in Airborne Thermal Image Processing for Landscape Assessment / New Approaches in Airborne Thermal Image Processing for Landscape Assessment

Pivovarník, Marek January 2017 (has links)
Letecká termální hyperspektrální data přinášejí řadu informací o teplotě a emisivitě zemského povrchu. Při odhadování těchto parametrů z dálkového snímání tepelného záření je třeba řešit nedourčený systém rovnic. Bylo navrhnuto několik přístupů jak tento problém vyřešit, přičemž nejrozšířenější je algoritmus označovaný jako Temperature and Emissivity Separation (TES). Tato práce má dva hlavní cíle: 1) zlepšení algoritmu TES a 2) jeho implementaci do procesingového řetězce pro zpracování obrazových dat získaných senzorem TASI. Zlepšení algoritmu TES je možné dosáhnout nahrazením používaného modulu normalizování emisivity (tzv. Normalized Emissivity Module) částí, která je založena na vyhlazení spektrálních charakteristik nasnímané radiance. Nový modul je pak označen jako Optimized Smoothing for Temperature Emissivity Separation (OSTES). Algoritmus OSTES je připojen k procesingovému řetězci pro zpracování obrazových dat ze senzoru TASI. Testování na simulovaných datech ukázalo, že použití algoritmu OSTES vede k přesnějším odhadům teploty a emisivity. OSTES byl dále testován na datech získaných ze senzorů ASTER a TASI. V těchto případech však není možné pozorovat výrazné zlepšení z důvodu nedokonalých atmosférických korekcí. Nicméně hodnoty emisivity získané algoritmem OSTES vykazují více homogenní vlastnosti než hodnoty ze standardního produktu senzoru ASTER.
50

Analysis of water vapour mixing ratio profiles in the Arctic from Raman lidar measurements during the MOSAiC-campaign

Seidel, Clara 04 April 2023 (has links)
For the first time, vertical water vapour profiles were measured in the Central Arctic North of 85°N during the MOSAiC campaign (Multidisciplinary drifting Observatory for the Study of Arctic Climate). Continuous measurements of the Raman lidar PollyXT are used to retrieve high-resolved vertical profiles of the water vapour mixing ratio (WVMR) during the polar night. The collected data are calibrated and evaluated by use of selected clear-sky profiles between 25 October 2019 and 29 February 2020. Three different calibration methods are applied using reference data from radiosonde launches or microwave radiometer (MWR) measurements, respectively. The calibration with the least error results from a linear fit between collocated radiosonde and lidar measurements and delivers a final calibration constant of 15.96 ± 0.37 g/kg for the period from 25 Oct 2019 to 29 Feb 2020. The calibrated WVMR profiles are analysed regarding the vertical distribution of water vapour in the Arctic, its impact on the downward thermal-infrared radiation (DTIR) at the surface, and its relation to the Arctic Oscillation (AO) index as a measure for the general atmospheric circulation. The Arctic atmosphere is very dry during the winter time with WVMR values below 2 g/kg. The vertical water vapour distribution is strongly related to the temperature profile. Layers with higher WVMR values are often capped by temperature inversions. Layers with higher integrated water vapour values (IWV) are located either close to the surface (coupled) or in an elevated layer (decoupled), related to local or advective processes, respectively. The impact of the vertical distributed water vapour on the clear-sky DTIR at the surface was investigated by evaluating the evolution of the air mass at the measurement location over several hours for seven clear-sky cases. The relation between the measured DTIR at the surface and the lidar IWV shows a linear correlation for each case, but with a shift in the radiation values depending on the temperature of the vertical distributed water vapour. The impact of the IWV on the DTIR is determined to be 9.33 − 15.03 W/kg from the example cases. Beside, a linear correlation is found between the temperature of the vertical distributed water vapour and the radiation temperature of the sky, which is derived from the Stefan-Boltzmann’s Law. Both results depict the high impact of the atmospheric water vapour profile on the surface energy budget during clear-sky winter conditions. The influence of the atmospheric circulation on the vertical water vapour distribution in the Arctic is investigated by use of the AO index. While very stable conditions with a weak exchange with lower latitudes are expected during the positive phase of the AO, a stronger meridional transport is related to the negative phase of the AO. The evaluation of 71 randomly selected clear-sky profiles shows differences in the amount and the vertical structure of each WVMR profile between the two phases. Higher WVMR values and layers with higher IWV are observed during the negative AO phase. Nonetheless, a high variability between dry and humid cases is seen during all phases of the AO due to synoptic events. Two main sources for water vapour in the Eastern Central Arctic are identified independent of the AO. These are cyclones on the one hand and the occurrence of a main wind direction from the seas north of Siberia namely Laptev, Kara and Barents Sea on the other hand. In summary, the thesis discusses different calibration methods for the derivation of WVMR profiles from Raman lidar measurements in its first part. In the second part, the thesis gives an overview over the vertical water vapour distribution in the Central Arctic winter and its complex relation to temperature profiles, radiation measurements at the surface and the atmospheric circulation.

Page generated in 0.0561 seconds