Analysis of Precipitable Water Vapour in Angola Using GNSS Observations

For accurate weather predictions and analysis of extreme events, a good estimate of the amount of water content in the atmosphere is essential. This information is provided by several techniques like radiosondes that measure this parameter at various heights. However, most of them are very limited spatially and temporarily or suffer from measurement specific constraints. To complement these techniques, Precipitable Water Vapor (PWV) can be measured with GNSS (Global Navigation Satellite System) at CORS (Continuously Operating Reference Stations) networks. when the temperature and pressure are also known at the station location. PWV can be derived from the delay in the GNSS signal when it passes through the troposphere. In the framework of SUGGEST-AFRICA, it is being implemented a system to use the national GNSS stations for the automatic computation of PWV in Angola. Thus, this dissertation intends to describe the necessary steps to develop a system to be used for supporting meteorological and climate applications in Angola. SUGGEST-AFRICA also funded the installation of 5 weather stations, collocated with GNSS stations in Angola namely: Benguela, Cabinda, Cuito, Luanda and Namibe, in order to obtain pressure and temperature which is necessary to obtain the PWV estimates. When there are no nearby meteorological stations, the potential alternative is to use values from global/regional models. Methodologies have been optimized to passive and actively access the GNSS data; the PWV estimations are computed using PPP (Precise Point Positioning), which permits the estimation of each station separately; solutions have been validated using internal values. In addition, analyses are presented to evaluate the reliability of the network. This work presents preliminary results for the variation of the ZTD data available all around the territory in Angola and how they relate to the seasonal variations in water vapour. Also, presents preliminary results for the time-series variation of PWV in the Luanda station (collocated by the SEGAL group). This study is supported by SUGGEST-AFRICA, funded by Fundação Aga Khan and FCT. It uses computational resources provided by C4G – Collaboratory for Geosciences (PINFRA/22151/2016). It is also supported by project FCT/UIDB/50019/2020 – IDL funded by FCT.Para precisão da previsão do tempo e análise de eventos extremos é fundamental uma boa estimativa do vapor da água na atmosfera. O vapor da água na atmosfera é fornecido por várias técnicas como radio sondagem que mede este parâmetro em várias alturas. No entanto, muito dessas técnicas são limitadas devido a resolução espacial e temporal ou sofrem restrições específicas de medição. Para completar estas limitações encontrado nas demais técnicas, o vapor da água precipitável (PWV) pode ser medido pelo GNSS (Sistemas de navegação global por satélite) CORS (Rede nacional de estações de referência de operação continua). PWV pode ser obtido a partir do atraso do sinal de GNSS através da troposfera, quando a temperatura e a pressão também são conhecidas derivado da localização duma estação meteorológica. No âmbito da SUGGEST-ÁFRICA, esta ser implementado um sistema de modo a calcular o PWV de uma maneira automática em Angola. Assim, nesta dissertação pretende descrever os passos necessários para desenvolver tal sistema a ser utilizado para apoiar aplicações meteorológicas e climáticas em Angola. SUGGEST-ÁFRICA também financiou a instalação de 5 estações meteorológicas, colocada com estações GNSS em Angola, nomeadamente: Benguela, Cabinda, Cuito, Luanda e Namibe, a fim de obter a pressão e a temperatura necessárias para obter as estimativas PWV. Aconselha-se o uso dos modelos globais/regionais para aquisição de valores de pressão e temperatura quando não existe dados nas estações meteorológicas adjacentes. As metodologias foram otimizadas para o acesso passivo e ativo dos dados GNSS; a estimação do vapor de água precipitável é calculada usando a técnica PPP (Posicionamento do ponto preciso), que permite a determinação de cada estação individualmente e separadamente; as soluções foram validadas usando valor interno. Além disso, são apresentadas análises para avaliar a fiabilidade da rede. Este trabalho, também apresenta resultados preliminares para a variação de todo dados do ZTD disponível em Angola e a forma como se relacionam com as variações sazonais do vapor de água. Também, apresenta variação da série temporal do PWV na estação meteorológica de Luanda (instalado pela SEGAL). Este estudo é suportado pela SUGGEST-ÁFRICA, financiado pela fundação Aga Khan e FCT. Utiliza recurso computacional fornecido pela C4G – Colaboração de Geociências (PINFRA/ 22151/2016). Também é apoiado pelo projecto FCT/UIDB/50019/2020 – IDL financiado pela FCT

Analysis of Precipitable Water Vapour in Nigeria using GNSS Observations

Water Vapour estimation using ground-based Global Navigation Satellite System (GNSS) observations is a well-established technology that contributes to weather forecast, research, and climate monitoring. Water vapour in the atmosphere is directly related with precipitation that may lead to extreme event (e.g., floods). The application of GNSS to sense the total amount of water vapour integrated along the signal path in the troposphere is what is referred to as GNSS meteorology. GNSS has the advantage of all-weather condition, low cost with high temporal and spatial resolution when compared to other classical methods of water vapour measuring that are expensive and/or with low spatial and temporal coverage. When GNSS signals are transmitted from GNSS satellites in space to ground-based GNSS receivers, they experience a tropospheric delay (an error source in GNSS positioning) often represented in GNSS meteorology as the Zenith Total Delay (ZTD). The ZTD is the sum of the Zenith Hydrostatic Delay and the Zenith Wet Delay and it is one of the products of GNSS data processing. The ZTD can be converted to Precipitable Water Vapour (PWV) when surface temperature and pressure values are known at the GNSS site using a conversion factor (?) that is dependent on the weighted mean temperature (Tm) and pressure. This dissertation focuses on the estimation and analysis of water vapour in Nigeria using GNSS observations. The Nigerian Permanent GNSS Network (NIGNET) stations observations and products were retrieved from the infrastructure implemented by Office of the Surveyor General of the Federation (OSGoF). Processing of the data was carried out using online software (GipsyX) for the estimation of ZTD. Fifteen GNSS stations were used in this research and the period 2009 to 2021 was considered. The characteristics of the ZTD over the territory of Nigeria was investigated. The range of ZTD variation in Nigeria for the period used in this research was found to be approximately between 1900mm to 2700mm in the NIGNET stations. The two main seasons in Nigeria were significantly noticed as low peaks were found to be occurring during the dry (winter) season while high peaks were remarkably seen during the rainy (summer) season. The amplitude of the seasonal variation within the period under investigation is between a minimum of 36mm to a maximum of 124mm with the Northern region having higher values than the Southern part. It was discovered ultimately by the results obtained from the analyses, that ZTD variation in both the Northern and Southern regions are influenced by the 4 distinct climates and other local weather conditions including temperature and the trade wind from Sahara Desert and the Atlantic Ocean.A estimativa de vapor de água usando observações do Sistema Global de Navegação por Satélite (GNSS) é uma tecnologia bem estabelecida que tem dado um contributo importante para a realização de previsões meteorológicas, investigação e monitorização climática. O vapor de água na atmosfera está diretamente relacionado com a precipitação que pode levar a eventos extremos (por exemplo, inundações). A área de estudo do uso de dados GNSS para detetar a quantidade total de vapor de água integrado ao longo do caminho do sinal na troposfera é designado de meteorologia GNSS. O GNSS tem como vantagem de poder ser utilizado em todas as condições climáticas, apresentar baixo custo e alta resolução temporal e espacial quando comparado a outros métodos clássicos de medição de vapor de água, normalmente mais caros e/ou com baixa cobertura espacial e temporal. Quando os sinais GNSS são transmitidos dose satélites para recetores terrestres, existe um atraso troposférico (uma fonte de erro no posicionamento GNSS) frequentemente representado na meteorologia GNSS como o Atraso Zenital Total (ZTD em Inglês ). O ZTD é a soma do Atraso Zenital e do Atraso Zenital Húmido e é um dos produtos do processamento de dados GNSS. O ZTD pode ser convertido em PWV quando os valores de temperatura e pressão da superfície são conhecidos no local através de um fator de conversão (?) que depende da temperatura média ponderada (Tm) e da pressão. Esta dissertação tem como objetivo a estimativa e análise de vapor de água na Nigéria usando observações GNSS. As observações e produtos das estações da Rede Permanente GNSS da Nigéria (NIGNET) foram obtidos através da infraestrutura implementada pelo OSGoF. O processamento dos dados foi realizado por meio de software online (GipsyX) para a estimativa do ZTD. Dados de quinze estações GNSS foram utilizadas na análise correspondendo ao período entre 2009 a 2021, para avaliar as características da ZTD sobre o território da Nigéria. A faixa de variação de ZTD na Nigéria para o período considerado foi de aproximadamente 1900mm a 2700mm nas estações NIGNET. As duas principais estações climáticas na Nigéria destacaram-se, com picos baixos que ocorreram durante a estação seca (inverno), e picos altos observados durante a estação chuvosa (verão). A amplitude da variação sazonal no período sob investigação é entre um mínimo de 36mm e um máximo de 124mm com a região norte tendo valores mais elevados que a região sul. Pelos resultados obtidos das análises foi ainda possível verificar que a variação da ZTD nas regiões Norte e Sul são influenciadas pelos 4 climas distintos e outras condições climáticas locais, incluindo temperatura e ventos alísios do deserto do Saara e do Oceano Atlântico

Atmospheric Instability Conditions during Rainy Seasons over Tanzania

The amount of rainfall and its distribution in time and space is dependent on the atmospheric instability conditions, and on its moisture content. The aim of this study was to determine the atmospheric instability conditions during January to March (JFM), February to April (FMA), March to May (MAM), and October to December (OND) rainy seasons over local climate zones in Tanzania. Zone area average seasonal Convective Available Potential Energy (CAPE), Convective Inhibition (CIN), Precipitable Water (PW) and Lifted index (Li) were calculated and analyzed. Results showed Li < 0 in JFM and FMA over whole Tanzania. During MAM and OND, Li < 0 over the Lake Zone, Western Highlands Zone and Central Zone only. CAPE ranged from 793 J/kg to 1183 J/kg during JFM, and 700 J/kg to 1080 J/kg during FMA. During MAM, CAPE ranged from 170 J/kg to 921 J/kg and from 173 J/kg to 833 J/kg during OND. Results also showed CAPE > 1000 J/kg over the Lake Zone, Western Highlands Zone, Island Zone, and Central Zone. These results show that the atmosphere was moderately unstable during the JFM and FMA and was weakly unstable during the MAM and OND. Therefore, the atmosphere is likely to be more convective during JFM and FMA seasons. Keywords: Lifted index, Convective inhibition, Precipitable water, Convective available potential energy, Atmospheric instability

BDS GNSS for Earth Observation

For millennia, human communities have wondered about the possibility of observing phenomena in their surroundings, and in particular those affecting the Earth on which they live. More generally, it can be conceptually defined as Earth observation (EO) and is the collection of information about the biological, chemical and physical systems of planet Earth. It can be undertaken through sensors in direct contact with the ground or airborne platforms (such as weather balloons and stations) or remote-sensing technologies. However, the definition of EO has only become significant in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit. Referring strictly to civil applications, satellites of this type were initially designed to provide satellite images; later, their purpose expanded to include the study of information on land characteristics, growing vegetation, crops, and environmental pollution. The data collected are used for several purposes, including the identification of natural resources and the production of accurate cartography. Satellite observations can cover the land, the atmosphere, and the oceans. Remote-sensing satellites may be equipped with passive instrumentation such as infrared or cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly called ’temporal resolution’), i.e., in a certain number of orbits around the Earth. The first remote-sensing satellites were the American NASA/USGS Landsat Program; subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the Chinese BuFeng-1 and Fengyun-3 series. Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers worldwide for a multitude of Earth monitoring and exploration applications. On the other hand, over the past 40 years, GNSSs have become an essential part of many human activities. As is widely noted, there are currently four fully operational GNSSs; two of these were developed for military purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation Satellite System (IRNSS/NavIC), will become available in the next few years, which will have enormous potential for scientific applications and geomatics professionals. In addition to their traditional role of providing global positioning, navigation, and timing (PNT) information, GNSS navigation signals are now being used in new and innovative ways. Across the globe, new fields of scientific study are opening up to examine how signals can provide information about the characteristics of the atmosphere and even the surfaces from which they are reflected before being collected by a receiver. EO researchers monitor global environmental systems using in situ and remote monitoring tools. Their findings provide tools to support decision makers in various areas of interest, from security to the natural environment. GNSS signals are considered an important new source of information because they are a free, real-time, and globally available resource for the EO community

Beyond 100: The Next Century in Geodesy

This open access book contains 30 peer-reviewed papers based on presentations at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). The meeting was held from July 8 to 18, 2019 in Montreal, Canada, with the theme being the celebration of the centennial of the establishment of the IUGG. The centennial was also a good opportunity to look forward to the next century, as reflected in the title of this volume. The papers in this volume represent a cross-section of present activity in geodesy, and highlight the future directions in the field as we begin the second century of the IUGG. During the meeting, the International Association of Geodesy (IAG) organized one Union Symposium, 6 IAG Symposia, 7 Joint Symposia with other associations, and 20 business meetings. In addition, IAG co-sponsored 8 Union Symposia and 15 Joint Symposia. In total, 3952 participants registered, 437 of them with IAG priority. In total, there were 234 symposia and 18 Workshops with 4580 presentations, of which 469 were in IAG-associated symposia. ; This volume will publish papers based on International Association of Geodesy (IAG) -related presentations made at the International Association of Geodesy at the 27th IUGG General Assembly, Montreal, July 2019. It will include papers associated with all of the IAG and joint symposia from the meeting, which span all aspects of modern geodesy, and linkages to earth and environmental sciences. It continues the long-running IAG Symposia Series

Atmospheric refraction and turbulence in VLBI data analysis

The progress in further improving the quality of results derived by space-geodetic techniques observing in the radio frequency domain, such as Very Long Baseline Interferometry (VLBI) or Global Navigation Satellite Systems (GNSS), is limited by rapid changes in the neutral part of the atmosphere. In particular, insufficient knowledge of the temporal and spatial refractivity variations restrict the attainable accuracy of the derived VLBI and GNSS target parameters. In the current model describing the additional propagation delay due to the neutral part of the atmosphere, only annual to hourly long periodic variations are taken into account. In contrast, small-scale fluctuations mainly originating from turbulent motions are generally neglected, although they form a serious error source for electromagnetic wave propagation. Dynamic processes in the neutral atmosphere additionally induce physical correlations in space and time, which are also largely ignored so far. Particularly with regard to future requirements, as, for instance, defined within the framework of the Global Geodetic Observing System established by the International Association of Geodesy, the current tropospheric model is not sufficient and needs to be improved. High rate GNSS data of 1 Hz sampling and below, and the VLBI Global Observing System with faster telescopes result in a better sampling of the atmosphere. However, new challenges emerge with respect to improved and proper analysis strategies, in particular to model the stochastic properties of atmospheric refraction, which represents a crucial issue in research and the main objective of this thesis. Quantifying and assessing the small-scale behavior of atmospheric refraction is extremely challenging, since small-scale characteristics of atmospheric refraction cannot be analyzed without sufficient knowledge of the stability of the VLBI observing system. An optimal experimental setup for both, investigations in atmospheric refraction and system stability issues, emerges from the commissioning phase of the twin radio telescope at the Wettzell Geodetic Observatory in Germany. Specially designed so-called WHISP sessions are scheduled, observed and analyzed within this thesis allowing to quantify the individual components of the observing system, in part for the first time. On this basis, refractivity fluctuations are quantified which are found to be in the range of 1-3 millimeters. A number of noteworthy conclusions has been drawn which would not have been possible without the novel observing approach. Special emphasis is also given to the development of an atmospheric turbulence model, which stochastically describes small-scale refractivity fluctuations due to turbulent motions in the neutral atmosphere. The results have produced an important contribution to the modeling of refraction effects in the neutral atmosphere now considering temporal and spatial correlations between the observations in a physical and meteorological way. By analyzing 2700 VLBI sessions including traditional and local observing networks, it is demonstrated that the incorporation of the newly devised model into the VLBI data analysis leads to an improvemen of the solutions compared to the standard strategies of the International VLBI Service for Geodesy and Astrometry, or other strategies refining the stochastic model of VLBI observations. Compared to other approaches addressing the issue of atmospheric turbulence, the model developed within this thesis has the advantage to be operationally efficient for routine mass analysis of VLBI observing sessions. Since the current atmospheric model reveals severe deficiencies with respect to the estimation of atmospheric parameters, new modeling and adjustment strategies are introduced to better describe the behavior of the neutral atmosphere. It is demonstrated that, in particular, the least squares collocation method ensures an improved modeling of the stochastic properties of the neutral atmosphere, which allows a zenith wet delay estimation in more meaningful and appropriate sense. The main achievements of this thesis are the development of an atmospheric turbulence model to improve the stochastic model of VLBI observations and the quantification of local atmospheric refraction variations in space and time. Both allows for new interpretations and model improvements in a stochastic and deterministic sense.Atmosphärische Refraktion und Turbulenzin der VLBI-Auswertung Die stetige Weiterentwicklung und Qualitätsverbesserung von Ergebnissen aus weltraum-geodätischen Verfahren im Radiofrequenzbereich, wie beispielsweise VLBI (Very Long Baseline Interferometry) oder GNSS (Global Navigation Satellite Systems), ist durch schnelle Veränderungen in der neutralen Atmosphäre limitiert. Die zu erreichende Genauigkeit von Stationskoordinaten, Erdrotationsparametern oder anderen Zielparametern wird durch die unzureichende Kenntnis räumlicher oder zeitlicher Variationen in der Refraktivität maßgeblich begrenzt. Das aktuelle Atmosphärenmodell in der Auswertung weltraum-geodätischer Verfahren sieht ausschließlich die Berücksichtigung langperiodischer Signale vor. Kleinskalige, überwiegend durch turbulentes Verhalten in der Atmosphäre hervorgerufene Fluktuationen werden hingegen weitestgehend vernachlässigt, obwohl sie einen nicht unerheblichen Einfluss auf die Ausbreitung elektromagnetischer Wellen haben. Des Weiteren induzieren dynamische Prozesse in der neutralen Atmosphäre sowohl räumliche als auch zeitliche Korrelation zwischen den Beobachtungen, die ebenfalls weitestgehend ignoriert werden. Insbesondere im Hinblick auf die von der IAG (International Association of Geodesy) formulierten GGOS (Global Geodetic Observing System) Ziele genügt das aktuelle Atmosphärenmodell nicht den zukünftigen Anforderungen. Zwar führen hoch aufgelöste GNSS-Daten mit Abtastfrequenzen von bis zu 1 Hz und eine neue Generation von schnelleren und präziseren sogenannten VGOS (VLBI Global Observing System) Radioteleskopen zu einer besseren Abtastung der Atmosphäre, jedoch entstehen auch neue Herausforderungen hinsichtlich einer verbesserten und geeigneteren Modellierung der stochastischen Eigenschaften atmosphärischer Refraktion, welche allgemein eine zentrale Fragestellung darstellt und folglich die wesentliche Aufgabe dieser Arbeit repräsentiert. Die Quantifizierung und Bewertung des Verhaltens der atmosphärischen Refraktion stellt eine große Herausforderung dar. Da insbesondere das kleinskalige Verhalten der atmosphärischen Refraktion eng mit den Stabilitätseigenschaften des VLBI-Beobachtungssystems zusammenhängt, müssen diese ausreichend gut bekannt sein. Durch die Inbetriebnahme des weltweit ersten Twin-Teleskops am Geodätischen Observatorium Wettzell in Deutschland entstanden optimale Voraussetzungen für die Detektion der Stabilitätseigenschaften des Beobachtungssystems sowie der atmosphärischen Refraktion. In dieser Arbeit wurden spezielle WHISPExperimente entworfen, die es erlauben, einzelne Komponenten des Beobachtungssystems zum Teil erstmalig zu quantifizieren. Auf dieser Grundlage wird auch der Einfluss von Variationen in der Refraktivität bestimmt, dem eine Größenordnung von 1-3 Millimetern zugerechnet wird. Ein besonderer Fokus liegt außerdem auf der Entwicklung eines Turbulenzmodells, welches zum einen zeitliche und räumliche Korrelationen zwischen den Beobachtungen berücksichtigt und zum anderen kleinskalige Fluktuationen in der Refraktivität stochastisch sowie physikalisch und meteorologisch sinnvoll beschreibt. Auf Basis der Auswertung von 2700 VLBI-Beobachtungssessionen unterschiedlicher Netzwerkgröße wird gezeigt, dass die Einführung des neuen Turbulenzmodells in die VLBI-Auswertung für die operationelle Auswertung geeignet ist und zu Verbesserungen gegenüber der Standardlösung des IVS (International VLBI Service for Geodesy and Astrometry) sowie alternativer Ansätze zur Verfeinerung des stochastischen Modells führt. Da das routinemäßig verwendete Atmosphärenmodell einige Defizite hinsichtlich der Schätzung atmosphärischer Parameter aufweist, werden in dieser Arbeit einige Modellierungs- und Ausgleichungsstrategien eingeführt, um die neutrale Atmosphäre besser zu charakterisieren. Es wird gezeigt, dass insbesondere die Kleinste-Quadrate-Kollokation eine verbesserte Modellierung der stochastischen Eigenschaften der neutralen Atmosphäre erlaubt und somit zu einer aussagekräftigeren und geeigneteren Schätzung der Atmosphärenparameter führt. Die Haupterrungenschaften dieser Arbeit sind die Entwicklung eines Turbulenzmodells zur Verbesserung des stochastischen Modells sowie die verbesserte Quantifizierung lokaler Refraktionseigenschaften in Raum und Zeit. Beides resultiert in neuen Interpretationsmöglichkeiten und Modellverbesserungen in deterministischer und stochastischer Hinsicht

Atmospheric refraction and turbulence in VLBI data analysis

The progress in further improving the quality of results derived by space-geodetic techniques observing in the radio frequency domain, such as Very Long Baseline Interferometry (VLBI) or Global Navigation Satellite Systems (GNSS), is limited by rapid changes in the neutral part of the atmosphere. In particular, insufficient knowledge of the temporal and spatial refractivity variations restrict the attainable accuracy of the derived VLBI and GNSS target parameters. In the current model describing the additional propagation delay due to the neutral part of the atmosphere, only annual to hourly long periodic variations are taken into account. In contrast, small-scale fluctuations mainly originating from turbulent motions are generally neglected, although they form a serious error source for electromagnetic wave propagation. Dynamic processes in the neutral atmosphere additionally induce physical correlations in space and time, which are also largely ignored so far. Particularly with regard to future requirements, as, for instance, defined within the framework of the Global Geodetic Observing System established by the International Association of Geodesy, the current tropospheric model is not sufficient and needs to be improved. High rate GNSS data of 1 Hz sampling and below, and the VLBI Global Observing System with faster telescopes result in a better sampling of the atmosphere. However, new challenges emerge with respect to improved and proper analysis strategies, in particular to model the stochastic properties of atmospheric refraction, which represents a crucial issue in research and the main objective of this thesis. Quantifying and assessing the small-scale behavior of atmospheric refraction is extremely challenging, since small-scale characteristics of atmospheric refraction cannot be analyzed without sufficient knowledge of the stability of the VLBI observing system. An optimal experimental setup for both, investigations in atmospheric refraction and system stability issues, emerges from the commissioning phase of the twin radio telescope at the Wettzell Geodetic Observatory in Germany. Specially designed so-called WHISP sessions are scheduled, observed and analyzed within this thesis allowing to quantify the individual components of the observing system, in part for the first time. On this basis, refractivity fluctuations are quantified which are found to be in the range of 1-3 millimeters. A number of noteworthy conclusions has been drawn which would not have been possible without the novel observing approach. Special emphasis is also given to the development of an atmospheric turbulence model, which stochastically describes small-scale refractivity fluctuations due to turbulent motions in the neutral atmosphere. The results have produced an important contribution to the modeling of refraction effects in the neutral atmosphere now considering temporal and spatial correlations between the observations in a physical and meteorological way. By analyzing 2700 VLBI sessions including traditional and local observing networks, it is demonstrated that the incorporation of the newly devised model into the VLBI data analysis leads to an improvement of the solutions compared to the standard strategies of the International VLBI Service for Geodesy and Astrometry, or other strategies refining the stochastic model of VLBI observations. Compared to other approaches addressing the issue of atmospheric turbulence, the model developed within this thesis has the advantage to be operationally efficient for routine mass analysis of VLBI observing sessions. Since the current atmospheric model reveals severe deficiencies with respect to the estimation of atmospheric parameters, new modeling and adjustment strategies are introduced to better describe the behavior of the neutral atmosphere. It is demonstrated that, in particular, the least squares collocation method ensures an improved modeling of the stochastic properties of the neutral atmosphere, which allows a zenith wet delay estimation in more meaningful and appropriate sense. The main achievements of this thesis are the development of an atmospheric turbulence model to improve the stochastic model of VLBI observations and the quantification of local atmospheric refraction variations in space and time. Both allows for new interpretations and model improvements in a stochastic and deterministic sense

Beyond 100: The Next Century in Geodesy

This open access book contains 30 peer-reviewed papers based on presentations at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). The meeting was held from July 8 to 18, 2019 in Montreal, Canada, with the theme being the celebration of the centennial of the establishment of the IUGG. The centennial was also a good opportunity to look forward to the next century, as reflected in the title of this volume. The papers in this volume represent a cross-section of present activity in geodesy, and highlight the future directions in the field as we begin the second century of the IUGG. During the meeting, the International Association of Geodesy (IAG) organized one Union Symposium, 6 IAG Symposia, 7 Joint Symposia with other associations, and 20 business meetings. In addition, IAG co-sponsored 8 Union Symposia and 15 Joint Symposia. In total, 3952 participants registered, 437 of them with IAG priority. In total, there were 234 symposia and 18 Workshops with 4580 presentations, of which 469 were in IAG-associated symposia. ; This volume will publish papers based on International Association of Geodesy (IAG) -related presentations made at the International Association of Geodesy at the 27th IUGG General Assembly, Montreal, July 2019. It will include papers associated with all of the IAG and joint symposia from the meeting, which span all aspects of modern geodesy, and linkages to earth and environmental sciences. It continues the long-running IAG Symposia Series

Izaña Atmospheric Research Center. Activity Report 2015-2016

This report is a summary of the many activities at the Izaña Atmospheric Research Center to the broader community. The combination of operational activities, research and development in state-of-the-art measurement techniques, calibration and validation and international cooperation encompass the vision of WMO to provide world leadership in expertise and international cooperation in weather, climate, hydrology and related environmental issues