Mitigation of Unmodeled Error to Improve the Accuracy of Multi-GNSS PPP for Crustal Deformation Monitoring

High-rate multi-constellation global navigation satellite system (GNSS) precise point positioning (PPP) has been recognized as an efficient and reliable technique for large earthquake monitoring. However, the displacements derived from PPP are often overwhelmed by the centimeter-level noise, therefore they are usually unable to detect slight deformations which could provide new findings for geophysics. In this paper, Global Positioning System (GPS), GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and BeiDou navigation satellite system (BDS) data collected during the 2017 Mw 6.5 Jiuzhaigou earthquake were used to further exploit the capability of BDS-only and multi-GNSS PPP in deformation monitoring by applying sidereal filtering (SF) in the observation domain. The equation that unifies the residuals for the uncombined and undifferenced (UCUD) PPP solution on different frequencies was derived, which could greatly reduce the complexity of data processing. An unanticipated long-term periodic error term of up to ± 3 cm was found in the phase residuals associated with BDS satellites in geostationary Earth orbit (GEO), which is not due to multipath originated from the ground but is in fact satellite dependent. The period of this error is mainly longer than 2000 s and cannot be alleviated by using multi-GNSS. Compared with solutions without sidereal filtering, the application of the SF approach dramatically improves the positioning precision with respect to the weekly averaged positioning solution, by 75.2%, 42.8%, and 56.7% to 2.00, 2.23, and 5.58 cm in the case of BDS-only PPP in the east, north, and up components, respectively, and 71.2%, 27.7%, and 37.9% to 1.25, 0.81, and 3.79 cm in the case of GPS/GLONASS/BDS combined PPP, respectively. The GPS/GLONASS/BDS combined solutions augmented by the SF successfully suppress the GNSS noise, which contributes to the detection of the true seismic signal and is beneficial to the pre- and post-seismic signal analysis

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

A Review of Selected Applications of GNSS CORS and Related Experiences at the University of Palermo (Italy)

Services from the Continuously Operating Reference Stations (CORS) of the Global Navigation Satellite System (GNSS) provide data and insights to a range of research areas such as physical sciences, engineering, earth and planetary sciences, computer science, and environmental science. Even though these fields are varied, they are all linked through the GNSS operational application. GNSS CORS have historically been deployed for three-dimensional positioning but also for the establishment of local and global reference systems and the measurement of ionospheric and tropospheric errors. In addition to these studies, CORS is uncovering new, emerging scientific applications. These include real-time monitoring of land subsidence via network real-time kinematics (NRTK) or precise point positioning (PPP), structural health monitoring (SHM), earthquake and volcanology monitoring, GNSS reflectometry (GNSS-R) for mapping soil moisture content, precision farming with affordable receivers, and zenith total delay to aid hydrology and meteorology. The flexibility of CORS infrastructure and services has paved the way for new research areas. The aim of this study is to present a curated selection of scientific papers on prevalent topics such as network monitoring, reference frames, and structure monitoring (like dams), along with an evaluation of CORS performance. Concurrently, it reports on the scientific endeavours undertaken by the Geomatics Research Group at the University of Palermo in the realm of GNSS CORS over the past 15 years

Application of Multi-GNSS Positioning in Landslide Surface Deformation Monitoring

With a modernization of legacy GPS and GLONASS systems, as well as with a finalization of the new European Galileo and Chinese BeiDou systems, about 120 navigation satellites for Global Navigation Satellite System (GNSS) users around the world are available presently. Usage of multi-GNSS constellations has therefore become an important research topic in recent years, including the area of landslide monitoring. The main goal of this dissertation thesis was to analyze and study positioning accuracy and performance of different satellite systems combinations with focus on finding the optimal strategy for multi-GNSS data collection and processing in landslide monitoring applications. Five stabilized monitoring points allowing repetitive GNSS observation campaigns were established at the selected Recica landslide in the Czech Republic. Quality of current multi-GNSS precise products provided by different analysis centers (ACs) was evaluated to allow a selection of the optimal one. Although no substantial differences were found, products provided by GeoForschungsZentrum (GFZ) and Center for Orbit Determination in Europe (CODE) can be recommended in overall. Consequently, positioning accuracy provided by various constellation combinations was analyzed by using data from well-established GNSS reference stations while simulating observation conditions of the Recica landslide. The best results were obtained when processing signals from a combination of GPS and GLONASS, or GPS, GLONASS and Galileo systems, with a static relative differential technique and observation periods for data collection exceeding eight hours. Finally, data from GNSS repetitive campaigns realized at the Recica landslide during two years were processed with optimal setup and obtained displacement results were compared to standard geotechnical measurements. A horizontal displacement with an annual velocity of about 3 cm in the horizontal direction was found for three monitoring points while the other two points were more stable.With a modernization of legacy GPS and GLONASS systems, as well as with a finalization of the new European Galileo and Chinese BeiDou systems, about 120 navigation satellites for Global Navigation Satellite System (GNSS) users around the world are available presently. Usage of multi-GNSS constellations has therefore become an important research topic in recent years, including the area of landslide monitoring. The main goal of this dissertation thesis was to analyze and study positioning accuracy and performance of different satellite systems combinations with focus on finding the optimal strategy for multi-GNSS data collection and processing in landslide monitoring applications. Five stabilized monitoring points allowing repetitive GNSS observation campaigns were established at the selected Recica landslide in the Czech Republic. Quality of current multi-GNSS precise products provided by different analysis centers (ACs) was evaluated to allow a selection of the optimal one. Although no substantial differences were found, products provided by GeoForschungsZentrum (GFZ) and Center for Orbit Determination in Europe (CODE) can be recommended in overall. Consequently, positioning accuracy provided by various constellation combinations was analyzed by using data from well-established GNSS reference stations while simulating observation conditions of the Recica landslide. The best results were obtained when processing signals from a combination of GPS and GLONASS, or GPS, GLONASS and Galileo systems, with a static relative differential technique and observation periods for data collection exceeding eight hours. Finally, data from GNSS repetitive campaigns realized at the Recica landslide during two years were processed with optimal setup and obtained displacement results were compared to standard geotechnical measurements. A horizontal displacement with an annual velocity of about 3 cm in the horizontal direction was found for three monitoring points while the other two points were more stable.548 - Katedra geoinformatikyvyhově

Geodesy: A look to the future

The report deals with the current and future uses of contemporary geodetic data and poses some questions and possibilities for the future. It is anticipated that the document will generate interest in present and future geodetic data for the solution of problems in Earth, ocean, and atmospheric sciences

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

Zur GNSS-basierten Bestimmung von Position und Geschwindigkeit in der Fluggravimetrie

Das weltumspannende Satelliten-Navigationssystem GNSS spielt eine wichtige Rolle für die Fluggravimetrie. Gegenstand dieser Arbeit ist die Entwicklung zuverlässiger GNSS-Algorithmen und Software für die hochgenaue GNSS-Datenanalyse in der Fluggravimetrie. Ausgehend von den Anforderungen für praktische Anwendungen der Fluggravimetrie lassen sich die Beiträge und Schwerpunkte dieser Dissertation wie folgt zusammenfassen: Ausgleichs- bzw. Schätzungs-Algorithmen: Ausgehend von den Genauigkeitsanforderungen an die GNSS-basierte Positionsbestimmung in der Fluggravimetrie werden in einer kinematischen GNSS-Daten-Auswertung eine Schätzung nach kleinsten Quadraten einschließlich der Eliminierung von Störparametern sowie ein Zwei-Wege-Kalman-Filter angewendet. Das Ziel der beiden Ausgleichsverfahren ist es, an jedem Messzeitpunkt zunächst globale Parameter (wie System-Fehler und Trägerwellen-Ambiguities) und anschließend lokale Parameter (wie Position und Geschwindigkeit der bewegten Messplattform) zu bestimmen. Die angewandten Methoden sind sehr effizient und ergeben hochpräzise Resultate für die GNSS-Datenanalyse. Analyse von Genauigkeit und Zuverlässigkeit: Die Genauigkeit und Zuverlässigkeit der Resultate der präzisen kinematischen GNSS-Positionsbestimmung werden untersucht. Dabei wird eine besondere Methode zur Bewertung der Genauigkeit der kinematischen GNSS-Positionsbestimmung vorgeschlagen, wo bekannte Entfernungen zwischen mehreren GNSS-Antennen als Genauigkeits-Maßstab genommen werden. Weiterhin wird der Einfluss der Uhrenfehler der GNSS-Empfänger auf die Genauigkeit der kinematischen Positionsbestimmung für die Hochgeschwindigkeits-Plattform untersucht. Für dabei auftretende Probleme wird eine Lösung vorgeschlagen. Algorithmen der kinematischen Positionsbestimmung die auf mehreren Referenzstationen beruhen: Um das Problem der im Falle langer Basislinien abnehmenden Genauigkeit in der relativen kinematischen GNSS-Positionsbestimmung zu bewältigen, wird ein neuer Algorithmus vorgeschlagen. Er beruht auf der apriori Einführung von Exzentrizitäts-Bedingungen für mehrere Referenzstationen. Dieser Algorithmus erhöht die Genauigkeit und Zuverlässigkeit der Ergebnise in der kinematischen Positionsbestimmung für große Regionen resp. lange Basislinien. Präzise GNSS-Positionsbestimmung, beruhend auf robuster Schätzung: Das Vorhandensein von groben Fehlern in den GNSS-Beobachtungen verursacht das Auftreten von Ausreißern in den Ergebnissen der Positionsbestimmung. Um dieses Problem zu überwinden, wird ein robuster Ausgleichungs-Algorithmus angewendet, der die Auswirkungen von gro-ben Fehlern in den Ergebnissen der kinematischen GNSS-Positionsbestimmung beseitigt. Kinematische Positionierung auf der Basis mehrerer bewegter Stationen: In der Fluggravimetrie werden in der Regel mehrere GNSS-Antennen auf einer bewegten Plattform installiert. In diesem Zusammenhang wird deshalb erstens ein kinematisches GNSS-Positionsbestimmungsverfahren vorgeschlagen, das auf mehreren gleichzeitig bewegten GNSS-Stationen basiert. Aus den bekannten, konstanten Distanzen zwischen den GNSS-Antennen werden dabei apriori Exzentrizitäts-Bedingungen abgeleitet und in die Positions-schätzung eingeführt. Dies verbessert die Zuverlässigkeit des Messsystems. Zweitens wird solch ein Ansatz auch zur Bestimmung eines gemeinsamen Refraktionsparameters aller GNSS-Antennen der Plattform für den feuchten Teil der Atmosphäre verwendet. Dieses Verfahren reduziert nicht nur die Menge der geschätzten Parameter, sondern verringert auch die Korrelation zwischen den atmosphärischen Parametern. Kinematische Positionierung basierend auf der Kombination verschiedener GNSS-Systeme: Um die Zuverlässigkeit und Genauigkeit der kinematischen Positionsbestimmung zu verbessern, werden die Signale mehrerer GNSS-Systeme (d.h. GPS und GLONASS) gemeinsam registriert und ausgewertet (sog. GNSS-Integration). Zur Optimierung des relativen Gewichts zwischen den Daten der verschiedenen GNSS-Systeme wird die Helmertsche Varianz-Komponenten-Schätzung angewandt. Der auf dieser Basis entwickelte Kombinationsalgorithmus ermöglicht die Verbesserung der Beiträge von mehreren GNSS-Systemen. Geschwindigkeitsbestimmung mit GNSS-Doppler-Daten: Die Auswertung der Schwere-Messdaten in der Fluggravimetrie verlangt die hochgenaue Bestimmung des Geschwindigkeitsvektors der bewegten Plattform. Deshalb werden rohe GNSS-Doppler-Beobachtungen verwendet, um die Geschwindigkeit der bewegten Plattform im Falle hoch-dynamischer Flugbedingungen kinematisch zu bestimmen. Darüberhinaus werden aus der Trägerphase abgeleitete Doppler-Beobachtungen verwendet, um präzise Geschwindigkeitsschätzungen im Falle weniger dynamischer Flugbedingungen zu erhalten. Die Kombination verschiedener GNSS-Systeme wird auch bei der Doppler-Geschwindigkeitsbestimmung angewandt. Hierzu wird die Anwendung der Helmertschen Varianzkomponenten-Schätzung und einer robusten Schätzung untersucht. Software Entwicklung und Anwendung: Um die aktuellen Anforderungen der GNSS-basierten Positionsbestimmung in der Flug- sowie Schiffsgravimetrie zu erfüllen, wurde ein Software-System (HALO_GNSS) für die präzise kinematische GNSS-Flugbahn- und Geschwindigkeitsberechnung kinematischer Plattformen entwickelt. Die in dieser Arbeit vorgeschlagenen Algorithmen wurden in diese Software integriert. Um die Effizienz der vorgeschlagenen Algorithmen und der HALO_GNSS Software zu prüfen, wurde diese Software sowohl in Flug- als auch in Schiffsgravimetrie-Projekten des GFZ Potsdam angewandt. Alle Ergebnisse werden verglichen und geprüft und es wird gezeigt, dass die angewandten Methoden die Zuverlässigkeit und Genauigkeit der kinematischen Positions- und Geschwindigkeitsbestimmung effektiv verbessern. Die Verwendung der Software HA-LO_GNSS ermöglicht kinematische Positionsbestimmung mit einer Genauigkeit von 1-2 cm sowie Geschwindigkeitsbestimmung mit einer Genauigkeit von ca. 1 cm/s mit Roh- und etwa 1 mm/s mit aus der Trägerphase abgeleiteten Doppler-Beobachtungen.The Global Navigation Satellite System (GNSS) plays a significant role in the fields of airborne gravimetry. The objective of this thesis is to develop reliable GNSS algorithms and software for kinematic highly precise GNSS data analysis in airborne gravimetry. Based on the requirements for practical applications in airborne gravimetry and shipborne gravimetry projects, the core research and the contributions of this thesis are summarized as follows: Estimation Algorithm: Based on the accuracy requirements for GNSS precise positioning in airborne gravimetry, the estimation algorithms of least squares including the elimination of nuisance parameters as well as a two-way Kalman filter are applied to the kinematic GNSS data post-processing. The goal of these adjustment methods is to calculate non-epoch parameters (such as system error estimates or carrier phase ambiguity parameters) using all data in the first step, followed by the calculation of epoch parameters (such as position and velocity parameters of the kinematic platform) at every epoch. These methods are highly efficient when dealing with massive amounts of data, and give the highly precise results for the GNSS data analyzed. Accuracy Evaluation and Reliability Analysis: The accuracy evaluation and reliability analysis of the results from precise kinematic GNSS positioning is studied. A special accuracy evaluation method in GNSS kinematic positioning is proposed, where the known distances among multiple antennas of GNSS receivers are taken as an accuracy evaluation index. The effect of the GNSS receiver clock error in the accuracy evaluation for GNSS kinematic positioning results of a high-speed motion platform is studied and a solution is proposed. Kinematic Positioning Based on Multiple Reference Stations Algorithms: In order to overcome the problem of decreasing accuracy in GNSS relative kinematic positioning for long baselines, a new relative kinematic positioning method based on a priori constraints for multiple reference stations is proposed. This algorithm increases the accuracy and reliability of kinematic positioning results for large regions resp. long baselines. GNSS Precise Positioning Based on Robust Estimation: In order to solve the problem of outliers occurring in positioning results which are caused by the presence of gross errors in the GNSS observations, a robust estimation algorithm is applied to eliminate the effects of gross errors in the results of GNSS kinematic precise positioning. Kinematic Positioning Based on Multiple Kinematic Stations: In airborne gravimetry, multiple antennas of GNSS receivers are usually mounted on the kinematic platform. Firstly, a GNSS kinematic positioning method based on multiple kinematic stations is proposed. Using the known constant distances among the multiple GNSS antennas, a kinematic positioning method based on a priori distance constraints is proposed to improve the reliability of the system. Secondly, such an approach is also used for the estimation of a common atmospheric wet delay parameter among the multiple GNSS antennas mounted on the platform. This method does not only reduce the amount of estimated parameters, but also decreases the correlation among the atmospheric parameters. Kinematic Positioning Based on GNSS Integration: To improve the reliability and accuracy of kinematic positioning, a kinematic positioning method using multiple GNSS systems integration is addressed. Furthermore, a GNSS integration algorithm based on Helmert’s variance components estimation is proposed to adjust the weights in a reasonable way. This improves the results when combining data of the different GNSS systems. Velocity Determination Using GNSS Doppler Data: Airborne gravimetry requires instantaneous velocity results, thus raw Doppler observations are used to determine the kinematic instantaneous velocity in high-dynamic environments. Furthermore, carrier phase derived Doppler observations are used to obtain precise velocity estimates in low-dynamic environments. Then a method of Doppler velocity determination based on GNSS integration with Helmert’s variance components estimation and robust estimation is studied. Software Development and Application: In order to fulfill the actual requirements of airborne as well as shipborne gravimetry on GNSS precise positioning, a software system (HALO_GNSS) for precise kinematic GNSS trajectory and velocity determination for kinematic platforms has been developed. In this software, the algorithms as proposed in this thesis were adopted and applied. In order to evaluate the effectiveness of the proposed algorithm and the HALO_GNSS software, this software is applied in airborne as well as shipborne gravimetry projects of GFZ Potsdam. All results are compared and examined, and it is shown that the applied approaches can effectively improve the reliability and accuracy of the kinematic position and velocity determination. It allows the kinematic positioning with an accuracy of 1-2 cm and the velocity determination with an accuracy of approximately 1 cm/s using raw and approximately 1 mm/s using carrier phase derived Doppler observations

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

Satellite Positioning

Satellite positioning techniques, particularly global navigation satellite systems (GNSS), are capable of measuring small changes of the Earths shape and atmosphere, as well as surface characteristics with an unprecedented accuracy. This book is devoted to presenting recent results and development in satellite positioning technique and applications, including GNSS positioning methods, models, atmospheric sounding, and reflectometry as well their applications in the atmosphere, land, oceans and cryosphere. This book provides a good reference for satellite positioning techniques, engineers, scientists as well as user community