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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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4D GPS water vapor tomography: new parameterized approaches / Donat Perler in Journal of geodesy, vol 85 n° 8 (August 2011)  

Public [article]  inJournal of geodesy > vol 85 n° 8 (August 2011) . - pp 539 - 550 Titre : 4D GPS water vapor tomography: new parameterized approaches Type de document : Article/Communication Auteurs : Donat Perler, Auteur ; Alain Geiger, Auteur ; Fabian Peter Hurter, Auteur Année de publication : 2011 Article en page(s) : pp 539 - 550 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] Alpes [Termes IGN] coordonnées ellipsoïdales [Termes IGN] distribution spatiale [Termes IGN] données GPS [Termes IGN] données météorologiques [Termes IGN] filtre de Kalman [Termes IGN] prédiction [Termes IGN] réfraction atmosphérique [Termes IGN] réfringence [Termes IGN] signal GPS [Termes IGN] Suisse [Termes IGN] tomographie [Termes IGN] troposphère [Termes IGN] vapeur d'eau [Termes IGN] voxel Résumé : (Auteur) Water vapor is a key variable in numerical weather prediction, as it plays an important role in atmospheric processes. Nonetheless, the distribution of water vapor in the atmosphere is observed with a coarse resolution in time and space compared to the resolution of numerical weather models. GPS water vapor tomography is one of the promising methods to improve the resolution of water vapor measurements. This paper presents new parameterized approaches for the determination of water vapor distribution in the troposphere by GPS. We present the methods and give first results validating the approaches. The parameterization of voxels (volumetric pixels) by trilinear and spline functions in ellipsoidal coordinates are introduced in this study. The evolution in time of the refractivity field is modeled by a Kalman filter with a temporal resolution of 30s, which corresponds to the available GPS-data rate. The algorithms are tested with simulated and with real data from more than 40 permanent GPS receiver stations in Switzerland and adjoining regions covering alpine areas. The investigations show the potential of the new parameterized approaches to yield superior results compared to the non parametric classical one. The accuracy of the tomographic result is quantified by the inter-quartile range (IQR), which is decreased by 10–20% with the new approaches. Further, parameterized voxel solutions have a substantially smaller maximal error than the non parameterized ones. Simulations show a limited ability to resolve vertical structures above the top station of the network with GPS tomography. Numéro de notice : A2011-359 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-011-0454-2 Date de publication en ligne : 08/03/2011 En ligne : https://doi.org/10.1007/s00190-011-0454-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31138 [article]

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Better weather prediction using GPS: water vapor tomography in the Swiss Alps / Simon Lutz in GPS world, vol 21 n° 7 (July 2010)

Public [article]  inGPS world > vol 21 n° 7 (July 2010) . - pp 40 - 47 Titre : Better weather prediction using GPS: water vapor tomography in the Swiss Alps Type de document : Article/Communication Auteurs : Simon Lutz, Auteur ; Donat Perler, Auteur ; Marc Troller, Auteur ; et al., Auteur Année de publication : 2010 Article en page(s) : pp 40 - 47 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] affaiblissement de la précision [Termes IGN] Alpes centrales [Termes IGN] atténuation du signal [Termes IGN] humidité de l'air [Termes IGN] prévision météorologique [Termes IGN] Suisse [Termes IGN] teneur en vapeur d'eau [Termes IGN] tomographie [Termes IGN] traitement du signal Résumé : (Editeur) [...] Forecasting ability has improved as measurement technology, communications, and the understanding of atmospheric processes have improved. Meteorologists use measure- ments from various types of sensors and mathematical models to predict its future state. Yet better sampling of the current state of the atmosphere, particularly water vapor, is needed to produce more accurate and more timely forecasts. GPS can help. The signals from the GPS satellites must transit the atmosphere on their way to a receiver on the Earth's surface. The atmosphere's atoms and molecules slow down the signals so that they arrive slightly later than they would if the Earth was surrounded by a vacuum, and this effect shows up in the GPS receiver measurements. The receiver or measurement processing software needs to remove or model the effect to obtain accurate receiver positions. On the other hand, if all parameters affecting GPS measurements such as satellite and receiver coordinates are well known, then the delay imparted by the atmosphere can be estimated. It is possible to separate the effect of water vapor from that of the dry gases such as nitrogen, oxygen, and carbon dioxide and to provide a measure of the atmosphere's moisture content. Several national weather agencies are ingesting such estimates from networks of GPS receivers into experimental or operational numerical weather forecast models. But these values represent an integrated measure of moisture above a receiver. Profiles of how moisture is distributed with height would be more useful and might lead to better weather forecasts. In this month's column, a team of Swiss researchers discuss how they use data from a network of GPS receivers and the technique of tomography to obtain such profiles. Numéro de notice : A2010-271 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30465 [article]

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