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GNSS meteorology in spatially dense networks / Fabian Peter Hurter (2014)  

Public Titre : GNSS meteorology in spatially dense networks Type de document : Thèse/HDR Auteurs : Fabian Peter Hurter, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2014 Collection : Astronomisch-Geodätische Arbeiten in der Schweiz, ISSN 0025-6676 num. 91 Importance : 185 Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-37-6 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Bernese [Termes IGN] données GNSS [Termes IGN] météorologie [Termes IGN] propagation du signal [Termes IGN] retard troposphérique zénithal [Termes IGN] signal GNSS [Termes IGN] station GNSS [Termes IGN] station météorologique [Termes IGN] teneur en vapeur d'eau [Termes IGN] traitement du signal Index. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (auteur) Two basic products from GNSS meteorology have been investigated in detail: (a) the Zenith Total Delay (ZTD) and, (b) wet refractivity fields reconstructed from Zenith Wet Delays (ZWD).The thesis aims at quantifying the accuracies of GNSS-derived ZTDs and refractivities and at characterizing their temporal and spatial resolution. In a first study using operational radiosondes and Global Navigation Satellite System (GNSS) data from the Swiss meteorological station in Payerne, the following uncertainty figures are obtained: With respect to the radiosonde, the GNSS-derived ZTD has a 1–3mm dry bias. Annual systematic variations of the comparison are found to have an amplitude of 1–2 mm . Removal of most systematic effects from the GNSS minus radiosonde ZTD time series plus a thorough budget of the radiosonde uncertainties allows the derivation of the random GNSS uncertainties. In the winter half-year, the standard deviation is shown to be 2.5–3.5 mm , during the summer half-year we obtain 3.5–5.0 mm. In a further study in the western part of Switzerland, wet refractivities have been derived on the basis of interpolated ZWDs from the Automatic GNSS Network for Switzerland (AGNES). The employed interpolation algorithm is termed least-squares collocation. It makes use of a deterministic function to describe the general parametric field and a correlation function describing the spatial and temporal correlations between the zenith wet delays. Corresponding wet refractivities show accuracies superior to results from tomographic reconstructions of a similar data set. Further inclusion of ground meteorological measurements of temperature and water vapour pressure im- prove the derived refractivities in the lowest 2 km of the troposphere. Radio occultations are added to the reconstruction. The data combination enables the extension of the radio occultation profiles down to the ground. It is also shown that the GNSS data largely contributes to the profile quality above the atmospheric boundary layer. Transformation of the wet refractivities to humidity values with temperature profiles from a radiometer in Payerne show accuracies of a similar order of mag nitude to those from numerical weather prediction analysis. Hence, application of the algorithm in nowcasting of rain or investigating boundary layer processes are envisaged. The third part of the thesis investigates the results from a campaign network of 34 geodetic- grade receivers. They were deployed close to and around Zermatt (Switzerland) for one month in summer 2010. The stations were spaced at distances of a few kilometers from each other and at heights between 1600–3500 m above mean sea level. The mountainous region provides an excellent natural laboratory to investigate the influences affecting the accuracy of the ZTD. Additionally, the Alpine region is prone to small-scale fluctuations in the troposphere. Thus, the spatial and temporal variability of the ZTD has been investigated. The influences of satellite obstructions, antenna and receiver types and a number of processing strategies on the estimated ZTD are analysed and validated with measurements from radiosondes launched during the campaign. The analysis suggests that 1 hour temporal resolution should not be undercut for estimated ZTDs. A temporal resolution of 30 minutes introduces more noise without better following the tropospheric fluctuation. The horizontal variability observed in ZTDs indicates correlation scale lengths of a few kilometers. From comparison with radiosondes, the ZTD uncertainty is shown to have 4–6 mm standard deviation. Some stations show signs of systematic effects caused by multipath and low- quality antenna patterns. Through the GNSS-inherent negative correlation of height with zenith delay, both parameters are similarly affected by these systematic influences. The performance of the numerical weather prediction model COSMO-2 is characterized in terms of integrated atmospheric state. The analysis yields preliminary recommendations on the assimilation of zenith total path delays into weather models in regions of highly complex topography such as the Swiss Alps. Note de contenu : 1 Introduction 1.1 Review of GNSS meteorology 1.2 Potential synergies with other water vapour measurements . 1.3 Challenges in GNSS meteorology 1.4 Objectives and structure of the thesis 2 Theory 2.1 Refractivity and path delay in the atmosphere 2.2 Collocation with the software COMEDIE 2.3 Water vapour tomography software AWATOS2 3 Comparison of zenith path delays from GNSS and radiosonde measurements 3.1 Data description 3.2 Formal uncertainties of ZTD estimates from GNSS 3.3 Comparison of ZTDs 3.4 Influence of processing strategy on GNSS ZTDs 3.5 2nd and 3rd order ionospheric effects . 3.6 Comparison of ZWDs 3.7 Formal uncertainty of radiosonde-derived ZTDs 3.8 Derivation of random GNSS ZTD uncertainty 3.9 Correlation between GNSS heights and ZTDs 3.10 Discussion . 3.11 Conclusion . 4 Payerne profile study 4.1 Abstract 4.2 Introduction 4.3 Description of data sets 4.4 Processing 4.5 Results . 4.6 Discussion 4.7 Conclusions 5 Geodetic water vapor campaign in Zermatt 5.1 Data description and processing 5.2 Troposphere results 5.3 Conclusions 6 Conclusions Numéro de notice : 12952 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère En ligne : http://www.sgc.ethz.ch/sgc-volumes/sgk-91.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76823

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Optical survey strategies and their application to space surveillance / Tim Flohrer (2012)  

Public Titre : Optical survey strategies and their application to space surveillance Type de document : Rapport Auteurs : Tim Flohrer, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2012 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 87 Importance : 178 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-34-5 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] débris spatial [Termes IGN] orbitographie [Termes IGN] stratégie [Termes IGN] surveillance Index. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (Editeur) [préface] This publication of Tim Flohrer focuses on strategies to search for space debris using optical observations and on the application of these strategies for space surveillance. The topic covers a wide range of aspects, starting with the actual detection of space debris on frames acquired by optical telescopes, and ending with the build-up and maintenance of a catalogue of orbit of these objects. An optimum search strategy aims at maximizing the number of observed objects of a reference population defined by the sizes and the orbital elements of the objects, by optimizing the observations sequences of telescopes at one or several sites. The design of the strategies must take into account geometrical boundary conditions – the objects must be visible from a given site – as well as radiometric constraints – the objects must be bright enough to be detected against the sky background. The build-up and maintenance of an orbit catalogue require periodic acquisition of astrometric positions of the catalogue objects. This may be achieved either by scheduling dedicated follow-up observations or by designing survey strategies in a way that enough observations of all objects are gained “incidentally”. All of the above-mentioned aspects are discussed in this publication. The author developed a software tool allowing to simulate search and observation strategies starting with the generation of individual observations and ending with a full orbit determination. This combination is rather unique and was a key element for the success of the strategies developed by Tim Flohrer. In addition to strategies for ground-based networks of telescopes the paper discusses concepts for the search of small size debris and for surveys of entire orbit regions using space-based optical sensors. The strategies to search for and monitor objects in the geostationary ring and the region of the global navigation satellite systems presented in this work became widely recognized in the scientific community. Concepts currently developed in the framework of the ESA initiative to establish an European space surveillance and tracking system are based to a great extent on Tim Flohrer’s work. Note de contenu : 1. Introduction and motivation 2. Space situational awareness, space debris, and space surveillance principles 2.1 Space situational awareness 2.2 Space surveillance 2.3 Space debris and its lifecycle 2.4 Space surveillance principles 2.5 Sensors with space surveillance capabilities 3. Observation fundamentals, data reduction, and orbit modelling 3.1 Reference systems 3.2 Orbital regimes 3.3 Observations 3.4 Orbits of artificial satellites 3.5 Two-line element (TLE) sets 4. Simulation environment for optical observations 4.1 PROOF 4.2 CelMech 4.3 Simulation environment 4.4 Application of the simulation environment to a proposed space-based optical observation scenario 4.5 Conclusions 5. Ground-based optical observation strategies 5.1 Population evolution 5.2 Accessibility of population 5.3 Proposed observation strategies 6. A system proposal for space-based optical space surveillance 6.1 SSA-related observation strategies with the SBO architecture 6.2 Radiometric characteristics of the SBO observing high altitudes 6.3 Coverage of reference populations 6.4 Orbit determination based on simulations 6.5 Conclusion 7. Conclusion and recommendations A. Performance of initial orbit determination from space-based observations B. Simulated orbit determination results for a system proposal for space-based optical space surveillance Numéro de notice : 15701 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Rapport de recherche En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-87.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62764

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15701-01	30.84	Livre	Centre de documentation	Géodésie	Disponible

Water vapor tomography using global navigation satellites systems / Donat Perler (2012)  

Public Titre : Water vapor tomography using global navigation satellites systems Type de document : Thèse/HDR Auteurs : Donat Perler, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2012 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 84 Importance : 188 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-30-7 Note générale : Bibliographie Doctoral Thesis Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] atmosphère terrestre [Termes IGN] données GNSS [Termes IGN] données météorologiques [Termes IGN] modélisation spatiale [Termes IGN] positionnement par GNSS [Termes IGN] rayonnement électromagnétique [Termes IGN] temps réel [Termes IGN] teneur en vapeur d'eau [Termes IGN] tomographie par GPS [Termes IGN] vapeur d'eau Index. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (Auteur) Water vapor plays an important role in the atmosphere. It is involved in many atmospheric processes and is a major contributor to the atmospheric energy budget and as such is a key quantity in numerical weather prediction (NWP) models. In recent years, NWP models gain in importance in hazard mitigation. But to provide precise quantitative forecasts, especially with respect to precipitation, we need accurate knowledge of the water vapor distribution in the atmosphere. Ground-based Global Navigation Satellite System (GNSS) tomography is a technique which can provide highly resolved and accurate water vapor profiles in space and time. The main objective of this thesis is to develop new tomographic algorithms which fulfill the requirements to assimilate refractivity measurements derived from GNSS into NWP models. A new tomography software called AWATOS 2 has been implemented. It is an assimilation system for point and integrated refractivity measurements. The tomographic model in AWATOS 2 is formulated as a Kalman filter and different voxel parameterizations are provided. The new trilinear and spline-based parameterizations allow a more accurate representation of the refractivity field without considerably increasing the number of unknowns. Advantages of these new parameterizations are a) more accurate results, b) point observations need not to be interpolated to the voxel centers and c) the tomographic solutions are at least C0-continuous in space. The stochastic prediction model implemented in AWATOS 2 relies on in-situ measurements and NWP model data. The prediction model is evaluated and adjusted with respect to data from the high-resolution NWP model COSMO-2 and from balloon soundings in Europe. In addition, AWATOS 2 provides a sophisticated simulation framework to carry out synthetic tests based on simple refractivity fields and on NWP model data. The algorithms of AWATOS 2 are assessed with synthetic tests and with real data in a longterm study using one year of data. The synthetic tests have confirmed the theoretical properties of the model such as a bias-free solution in case of bias-free input data, fast convergence rates, and the capability to resolve vertical structures in the wet refractivity field. In the long-term study, a root-mean-square (RMS) error of 3.0 ppm (0.4 gm3 absolute humidity) is achieved with respect to the NWP model COSMO-7. The investigations have shown that the newly introduced voxel parameterizations lead to significantly more accurate results than the classical constant parameterization. The improvements are about 15% with respect to balloon soundings and 5% with respect to NWP analysis data. The performance of the trilinear and spline-based parameterizations are similar. Further investigations have revealed the importance of a bias correction model. A newly developed bias correction model has decreased the RMS error with respect to the NWP model analysis from 4.9 ppm (0.7 gm3) to 3.0 ppm (0.4 gm3) using the spline parameterization. For the other parameterizations, the improvements are significantly smaller. The systematic differences corrected here are mainly caused by a) systematic differences between GPS tropospheric path delays and the NWP model data and b) by discretization errors. Another error source is related to the departure of the NWP model’s topography from the true one which can amount to several hundred meters in alpine areas. Investigations have shown that processes near the Earth’s surface have a strong impact on the wet refractivity. Therefore, differences between the true topography and that of the NWP model can cause substantial errors. This topic has to be addressed if GNSS observations are assimilated into NWP models in complex terrain. Considerable progress has been made in the field of low-cost GNSS receivers in recent years allowing to build dense networks at low costs. Furthermore, the existing GNSSs are improved and new ones are being launched. These developments offer new possibilities in GNSS tomography. With error analyses, the potential of such improvements for GNSS tomography have been investigated The use of GPS together with Galileo has the potential to improve the formal accuracy of the GNSS tomography by 10-15% compared to a GPS-only solution. In Switzerland, equipping the SwissMetNet with GNSS receivers would increase the number of GNSS stations from 31 to 91. This would improve the formal accuracy of the tomographic solution by about 20-25%. The investigations have shown that the improvements obtained by a more dense network and additional GNSSs are cumulative. Placing the stations on different altitudes and choosing locations with good satellite visibility are important to achieve accurate results and should be considered in the design of GNSS networks. All investigations have demonstrated that accurate 4D distributions of the wet refractivity in the troposphere can be estimated with GNSS tomography. The work has also revealed the possibilities and limitations of GNSS tomography in view of the assimilation into NWP models and proposes solution strategies to overcome the limitations. Note de contenu : 1 Introduction 1.1 Significance of tropospheric water vapor measurements 1.2 A short review of the research in GNSS tomography 1.3 Objectives and structure of the thesis 2 Introduction to the propagation of radio waves in the atmosphere 2.1 Propagation of radio waves in the atmosphere 2.2 Modeling the path delay 3 GNSS tomography with the software package AWATOS 2 3.1 Overview of AWATOS 2 3.2 Preprocessing of GNSS double difference delays 3.3 Discretization of the refractivity field and parameterization 3.4 Modeling the refractivity field with the Kalman filter approach 3.5 Simulation capabilities in AWATOS 2 4 Overview of the data sets 4.1 GPS data 4.2 Balloon soundings 4.3 Synoptic network SwissMetNet 4.4 Numerical weather prediction model COSMO 5 Description of the wet refractivity field 5.1 Tempo-spatial variation of the wet refractivity field 5.2 Discretization Error 5.3 Representation of the discretization error . 5.4 Investigations of the process noise using a random walk model 5.5 Conclusions 6 Comparison of balloon sounding data and GNSS-derived zenith path delays 6.1 Error budget of meteorological sensors 6.2 Intercomparison between zenith path delays of different sources 6.3 Conclusions 7 Potential of new GNSSs and dense networks in view of GNSS tomography 7.1 Configurations 7.2 Methods 7.3 Results and discussion 7.4 Conclusions 8 Simulation-based evaluation of the new tomographic algorithms 8.1 Theoretical considerations of the resolvability of vertical structures 8.2 Experiments with simulated data 8.3 Conclusions 9 Evaluation of the GPS tomography with a long-term study 9.1 Configuration and evaluation methods 9.2 Results and discussion 9.3 Bias correction model and its evaluation 9.4 Conclusions 10 Conclusions 11 Outlook Numéro de notice : 15546 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-006875504 En ligne : http://dx.doi.org/10.3929/ethz-a-006875504 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62758

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15546-01	30.84	Livre	Centre de documentation	Géodésie	Disponible

GPS based determination of the integrated and spatially distributed water vapor in the troposphere / Marc Troller (2004)  

Public Titre : GPS based determination of the integrated and spatially distributed water vapor in the troposphere Type de document : Thèse/HDR Auteurs : Marc Troller, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2004 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 67 Importance : 172 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-10-9 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] correction troposphérique [Termes IGN] distribution spatiale [Termes IGN] modèle atmosphérique [Termes IGN] positionnement par GPS [Termes IGN] propagation troposphérique [Termes IGN] Suisse [Termes IGN] teneur en vapeur d'eau [Termes IGN] tomographie [Termes IGN] traitement du signal [Termes IGN] troposphère [Termes IGN] vapeur d'eau Index. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (Auteur) Climate change and global warming have become a major challenge for the sustainable development of our Earth and its environment. Intensive research is carried out to understand atmospheric processes and their implications. In this content, water vapor plays a key role. It is an important component of the global energy balance and is involved in many chemical reactions. In microwave measurements, the tropospheric refractivity causes a delay in the arrival of the signal propagating through the atmosphere. This refraction effect is one of the limiting factors in accurate GPS positioning. The tropospheric path delay can be decomposed into a dry and wet part, where the latter part is coupled with the integrated precipitable water vapor above the GPS receiver. On the one hand, the refraction effect has to be corrected for GPS measurements, on the other hand, it is a valuable signal to determine the spatial distribution of the water vapor. This study investigates both aspects. For the first part, two basic approaches are looked into: One method is based on meteorological measurements. Thereby, the integrated amount of water vapor and its temporal variation are the prime target. The other concept makes use of long-term GPS measurements. The arrival delay of the GPS signals are used, to estimate the integrated amount of water vapor. This result can then be the basis to determine its spatial distribution and temporal behavior. The investigation is based on a tomographic approach and forms the main content of part 2 of this work. In part 1, an extension of the software package COMEDIE is developed and applied to determine tropospheric path delays. COMEDIE allows a four-dimensional modeling (in space and time) of the meteorological parameters air pressure, temperature and water vapor pressure using a collocation approach. Integrating the meteorological parameters, tropospheric path delays are obtained. Evaluations and comparisons in Switzerland show the performance of this method. An overall good agreement was achieved compared to GPS-estimated path delays. The accuracy depends on the season, and is in the range of 1-2 cm for the tropospheric path delay. Continuous GPS measurements allow to estimate tropospheric path delays in the GPS processing. In a second approach of part 1, a method based on such GPS-estimated path delays is developed. It uses - like COMEDIE - a four-dimensional model and a collocation adjustment to estimate tropospheric path delays at desired locations. Evaluations are carried out in the area of Switzerland using the permanent GPS network AGNES. Long-term time series of cross-correlations are analyzed. An accuracy of 0.5 - 1.5 cm is obtained. To resolve the GPS-estimated water vapor in the vertical, a tomographic approach is investigated in part 2 of this study. It is based on the assimilation of GPS double-difference observations. The wet refractivity field is determined applying a least-squares adjustment. To test the performance of the software, different weather conditions are simulated. Various stochastically constrained models are applied and discussed in terms of inversion stability. Results from real data gathered during a dedicated measurement campaign in the high density GPS network of the Big Island of Hawaii are analyzed. Compared to radiosondes, an accuracy of about 10 ppm (refractivity units) is achieved. To compare the potential and limits of the investigated methods, independent data must be available. An extensive study is performed in the area of Switzerland to evaluate and compare all presented methods with each other. For the validation, data of the numerical weather model aLMo are used. Seven days of data in a high spatial distribution and on an hourly basis are investigated. The tropospheric path delays resulting from the various methods are compared and analyzed. An overall good agreement with the aLMo data was observed. To evaluate the spatial distribution of water vapor, 7680 refractivity profiles are determined with the tomographic method and compared with the numerical weather data. The analysis contains four tomographic approaches including different types of constraints. The results are statistically evaluated and compared. A correlation between the accuracy and the weather situation was found. Overall, an agreement of 5-7 ppm (refractivity units) was achieved compared to aLMo. In conclusion, it can be stated that the determination of the integrated amount of water vapor in the troposphere was successfully performed. For the main geodetic application, the correction of GPS measurements, the estimation of path delays in the GPS processing is recommended, provided long-terrn GPS phase observations are available. For the determination of the spatial distribution and the temporal variation of the integrated amount of water vapor, modeling of the GPS-estimated path delays is a successful method. Moreover, the principal feasibility to resolve the vertical distribution of the water vapor applying the tomographic approach was demonstrated. However, further investigations concerning constraints or the introduction of additional information are required. Numéro de notice : 13264 Affiliation des auteurs : non IGN Autre URL associée : http://dx.doi.org/10.3929/ethz-a-004796376 Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-004796376 En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-67.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=54945

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13264-01	30.84	Livre	Centre de documentation	Géodésie	Disponible
13264-02	30.84	Livre	Centre de documentation	Géodésie	Disponible

Spatial and temporal distribution of atmospheric water vapor using space geodetic techniques / Lars Peter Kruse (2001)  

Public Titre : Spatial and temporal distribution of atmospheric water vapor using space geodetic techniques Type de document : Thèse/HDR Auteurs : Lars Peter Kruse, Auteur Editeur : Zurich : Schweizerischen Geodatischen Kommission / Commission Géodésique Suisse Année de publication : 2001 Collection : Geodätisch-Geophysikalische Arbeiten in der Schweiz, ISSN 0257-1722 num. 61 Importance : 128 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-908440-03-1 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] analyse comparative [Termes IGN] atmosphère terrestre [Termes IGN] distribution spatiale [Termes IGN] données GPS [Termes IGN] modèle atmosphérique [Termes IGN] temps réel [Termes IGN] teneur en vapeur d'eau [Termes IGN] tomographie [Termes IGN] troposphère [Termes IGN] vapeur d'eau [Termes IGN] water vapour radiometer Index. décimale : 30.84 Applications de géodésie spatiale à l'atmosphère Résumé : (Auteur) This work investigates methodological aspects of the Global Positioning System (GPS) to validate its potential as a remote sensing tool for monitoring atmospheric water vapor. GPS estimates of integral precipital water vapor (IPWV) are compared with simultaneous measurements of collocated Water Vapor Radiometers (WVR), as well as atmospheric refraction models for validation of GPS for meteorological applications. Based on a one year data set of continuous GPS estimates and WVR observations at ETH Zurich a standard deviation of 1.54 mm and an offset of 0.54 mm IPWV is found between the two techniques. The analysis of several dedicated observation campaigns carried out at different sites in Europe and on Hawaii revealed offsets between GPS estimates and WVR observations. The instrumental methods are also compared with a numerical model of the troposphere using ground meteorological observations and radiosondes from the station Payerne of the Swiss meteorological network (ANETZ). The modeling results, obtained with a software package performing four-dimensional interpolations by collocation yield a standard deviation of 2.88 mm and a bias of 2.23 mm IPWV with respect to the GPS derived time series of IPWV. Furthermore a clear seasonal dependency of the GPS - WVR differences is recognized. Mainly the periods dominated by strong fluctuations of water vapor during summer and autumn months degrade the agreement between the two techniques. Because of the high correlation between GPS estimated tropospheric parameters and the height component, potential error sources are investigated. The accuracy of GPS-derived IPWV in near real-time for consideration in weather forecasting is degraded due to insufficient satellite orbit quality. Investigations on the impact of implementing predicted orbit information on GPS water vapor retrievals showed that the accuracy degrades by a factor of about 2 compared to results obtained with final precise orbits as released by the International GPS Service (IGS) about two weeks after the observations. Finally the potential of GPS for resolving three-dimensional distributions of tropospheric water vapor by means of the tomographic technique is investigated and applied within this work. For this purpose a software package called AWATOS (Atmospheric WAter vapor TOmography Software) was developed. In order to validate the tomographic approach a dedicated field experiment was carried out on the Big Island of Hawaii, USA. Tomographic results based on the extremely dense Continuous GPS (CGPS) network in the Mt. Kilauea and Mauna Loa volcano area are presented. They are compared to other independent techniques, such as radiosondes, Water Vapor Radiometers, and a high resolution solar spectrometer. Numéro de notice : 13061 Affiliation des auteurs : non IGN Autre URL associée : http://dx.doi.org/10.3929/ethz-a-003884306 Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-003884306 En ligne : https://www.sgc.ethz.ch/sgc-volumes/sgk-61.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=54862

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
13061-02	30.84	Livre	Centre de documentation	Géodésie	Disponible
13061-01	30.84	Livre	Centre de documentation	Géodésie	Disponible

Bestimmung des Gesamtelektroneninhalts der Ionosphäre aus PRARE-Entfernungs- und Dopplerbeobachtungen / Frank Flechtner (2000)

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Mapping and predicting the Earth's ionosphere using the Global Positioning System / Stefan Schaer (1999)  

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Geophysical distributions of occultations of GPS satellites viewed from a low Earth orbiting satellite / D.M. O'Brien (1998)

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Ionosphere and geodetic satellite systems / Urs Wild (1994)  

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The application of spaceborne atmospheric limb sounding and global change monitoring / W.G. Melbourne (1994)

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Altimetric ionospheric correction using DORIS Doppler data / P. Escudier (1991)

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