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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)
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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 signalRésumé : (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
in GPS world > vol 21 n° 7 (July 2010) . - pp 40 - 47[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 067-2010071 RAB Revue Centre de documentation En réserve L003 Disponible GPS based determination of the integrated and spatially distributed water vapor in the troposphere / Marc Troller (2004)
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'eauIndex. 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 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 13264-01 30.84 Livre Centre de documentation Géodésie Disponible 13264-02 30.84 Livre Centre de documentation Géodésie Disponible GPS Tomography and Remote Sensing Techniques for Water Vapor Determination in the ESCOMPTE Campaign / Beat Bürki (2004)
contenu dans Celebrating a decade of the International GPS Service, Workshop & Symposium 2004 / Michael Meindl (2004)
Titre : GPS Tomography and Remote Sensing Techniques for Water Vapor Determination in the ESCOMPTE Campaign Type de document : Article/Communication Auteurs : Beat Bürki, Auteur ; Simon Lutz, Auteur ; Marc Troller, Auteur ; Alexander Somieski, Auteur ; Andrea Walpersdorf, Auteur ; Erik Doerflinger, Auteur ; Alain Geiger, Auteur ; Olivier Bock , Auteur ; et al., Auteur Editeur : Berne : Université de Berne Année de publication : 2004 Conférence : IGS 2004, international symposium, Celebrating a decade of the International GPS Service Symposium 01/03/2004 05/03/2004 Berne Suisse Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale
[Termes IGN] positionnement par GPS
[Termes IGN] teneur en vapeur d'eau
[Termes IGN] tomographieRésumé : (Auteur) The hierarchy of reference frames used in the IGS and the procedures and rationale for realizing them are reviewed. The Conventions of the IERS lag developments in the IGS in a number of important respects. Recommendations are offered for changes in the IERS Conventions to recognize geocenter motion (as already implemented by the IGS) and to enforce greater model consistency in order to achieve higher precision for combined reference frame products. Despite large improvements in the internal consistency of IGS product sets, defects remain which should be addressed in future developments. If the IGS is to remain a leader in this area, then a comprehensive, long-range strategy should be formulated and pursued to maintain and enhance the IGS reference frame, as well as to improve its delivery to users. Actions should include the official designation of a high-performance reference tracking network whose stations are expected to meet the highest standards possible. Numéro de notice : C2004-016 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=65027