International GNSS Service: Technical Report 2021

Applications of the Global Navigation Satellite Systems (GNSS) to Earth Sciences are numerous. The International GNSS Service (IGS), a voluntary federation of government agencies, universities and research institutions, combines GNSS resources and expertise to provide the highest–quality GNSS data, products, and services in order to support high–precision applications for GNSS–related research and engineering activities. This IGS Technical Report 2021 includes contributions from the IGS Governing Board, the Central Bureau, Analysis Centers, Data Centers, station and network operators, working groups, pilot projects, and others highlighting status and important activities, changes and results that took place and were achieved during 2021

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

Undifferenced and Uncombined GNSS Time Transfer and its Space Applications

This thesis presents a framework for developing a state-of-the-art undifferenced and uncombined (UDUC) time transfer technique for space applications. It addresses challenges in GNSS time transfer, such as multi-frequency signal modelling, satellite clock estimation, and hardware delay variations. The thesis introduces the UDUC POD method for GNSS time transfer in space and explores the feasibility of constructing a LEO-based space-time reference. This PhD dissertation is among the first to investigate the UDUC GNSS time transfer

Contribution of GNSS CORS Infrastructure to the Mission of Modern Geodesy and Status of GNSS CORS in Thailand

Geodesy is the science of measuring and mapping the geometry, orientation and gravity field of the Earth including the associated variations with time. Geodesy has also provided the foundation for high accuracy surveying and mapping. Modern Geodesy involves a range of space and terrestrial technologies that contribute to our knowledge of the solid earth, atmosphere and oceans. These technologies include: Global Positioning System/Global Navigation Satellite Systems (GPS/GNSS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), Satellite Altimetry, Gravity Mapping Missions such as GRACE, CHAMP and GOCE, satelliteborne Differential Interferometric Synthetic Aperture Radar (DInSAR), Absolute and Relative Gravimetry, and Precise Terrestrial Surveying (Levelling and Traversing). A variety of services have been established in recent years to ensure high accuracy and reliable geodetic products to support geoscientific research. The reference frame defined by Modern Geodesy is now the basis for most national and regional datums. Furthermore, the GPS/GNSS technology is a crucial geopositioning tool for both Geodesy and Surveying. There is therefore a blurring of the distinction between geodetic and surveying GPS/GNSS techniques, and increasingly the ground infrastructure of continuously operating reference stations (CORS) receivers attempts to address the needs of both geodesists and other positioning professionals. Yet Geodesy is also striving to increase the level of accuracy by a factor of ten over the next decade in order to address the demands of “global change” studies. The Global Geodetic Observing System (GGOS) is an important component of the International Association of Geodesy. GGOS aims to integrate all geodetic observations in order to generate a consistent high quality set of geodetic parameters for monitoring the phenomena and processes within the “System Earth”. Integration implies the inclusion of all relevant information for parameter estimation, implying the combination of geometric and gravimetric data, and the common estimation of all the necessary parameters representing the solid Earth, the hydrosphere (including oceans, ice-caps, continental water), and the atmosphere. This paper will describe the background to the establishment of GGOS, discuss the important role to be played by GPS/GNSS infrastructure in realising the GGOS mission and provide an update status of GNSS CORS in Thailand

Global and Regional Navigation Satellite Systems: Security and Defense Applications and Intentional Threats against them

Η δορυφορική πλοήγηση είναι μία διαστημική ικανότητα που παρέχει υπηρεσίες σχετικές με πληροφορίες για τη θέση, την ταχύτητα και τον χρόνο σε χρήστες εξοπλισμένους με κατάλληλους δέκτες και που σήμερα έχει μεγάλη επιρροή στην καθημερινή μας ζωή. Επί του παρόντος, τέσσερα παγκόσμια δορυφορικά συστήματα πλοήγησης με παγκόσμια κάλυψη βρίσκονται σε λειτουργίαˑ επιπλέον, υπάρχουν δύο περιφερειακά δορυφορικά συστήματα πλοήγησης που καλύπτουν μόνο συγκεκριμένες περιοχές. Σε αυτή τη διπλωματική εργασία περιγράφονται η δορυφορική πλοήγηση και οι βασικές αρχές λειτουργίας της. Παρουσιάζονται τα παγκόσμια και τα περιφερειακά δορυφορικά συστήματα πλοήγησης, καθώς και μία τεχνική σύγκριση μεταξύ αυτών των συστημάτων. Αυτή η διπλωματική εργασία κάνει επίσης μία συζήτηση για τις εφαρμογές της δορυφορικής πλοήγησης που αφορούν σε θέματα ασφάλειας και άμυνας, τα οποία είναι πολύ σημαντικά και στους δύο τομείς, τον στρατιωτικό και τον πολιτικό. Παρουσιάζονται οι σκόπιμες απειλές εναντίον των δορυφορικών συστημάτων πλοήγησης, δηλαδή οι παρεμβολές θορύβου και παραπλάνησης του σήματος αυτών των συστημάτων και συζητούνται οι πιο σημαντικές τεχνικές ανίχνευσης και μείωσης αυτών των απειλών. Τα συμπεράσματα της διπλωματικής εργασίας επικεντρώνονται στη βελτίωση της απόδοσης των δορυφορικών συστημάτων πλοήγησης και στην ελάττωση της τρωτότητας αυτών των συστημάτων απέναντι στις σκόπιμες παρεμβολές εναντίον τους.Satellite navigation is a space capability that provides positioning, velocity and time information to users equipped with the suitable receiver and today has a significant influence on everyday life. Currently, four global navigation satellite systems with global coverage are operational; furthermore, two regional navigation satellite systems cover only specific areas. In this master thesis satellite navigation and its basic principles of operation are described. The global and the regional navigation satellite systems as well as a technical comparison between these systems are presented. This thesis also discusses satellite navigation applications concerning security and defense issues, which are of great importance for both military and civil sectors. The intentional threats against the navigation satellite systems, that is, jamming and spoofing interference of the signal of these systems, are presented and some of the most important techniques for detection and mitigation of these threats are discussed. The conclusions of this thesis concentrate on improving the performance of the navigation satellite systems, and reducing the vulnerability of these systems towards the intentional interference against them

IGS Technical Report 2013

Applications of the Global Navigation Satellite Systems (GNSS) to Earth Sciences are numerous. The International GNSS Service (IGS), a federation of government agencies, universities and research institutions, plays an increasingly critical role in support of GNSS–related research and engineering activities. This Technical Report 2013 includes contributions from the IGS Governing Board, the Central Bureau, Analysis Centers, Data Centers, station and network operators, and others highlighting status and important activities, changes and results that took place and were achieved during 2013

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

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