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

Aspectos técnico-científicos de barragens no Brasil: uma abordagem teórica

The safety of a dam is the result of a series of factors, including structural, geotechnical, hydraulic, operational and environmental aspects. In Brazil, Law No. 12.334 of September 2010 establishes the National Dam Safety Policy, which requires safety reports and monitoring inspections for existing dams. The inspection comprises a set of devices installed on the dam, which are used to assess the structural behavior based on performance parameters of the structure, such as displacements, flows, stresses, slopes and others. Dam auscultation procedures, historically, have been performed since the 1950s. Since then, there have been significant advances in instrumentation and dam auscultation methods. This work presents a theoretical approach on technical and scientific aspects of dams in Brazil, based on a state-of-the-art literature review, involving auscultation of dams in the context of design codes, concepts, instrumentation, safety, procedures and monitoring methods.A segurança de uma barragem é resultante de uma série de fatores, dentre os quais podem ser citados aspectos estruturais, geotécnicos, hidráulicos, operacionais e ambientais. No Brasil, a Lei nº 12.334 de setembro de 2010 estabelece a Política Nacional de Segurança de Barragens. A instrumentação compõe um conjunto de dispositivos instalados nas barragens, que são utilizados para avaliar o seu comportamento estrutural a partir de parâmetros de desempenho da estrutura, tais como deslocamentos, vazões, tensões, inclinações e outros. Procedimentos de auscultação de barragens, historicamente, tem sido realizado desde a década de 50, conforme a literatura. Desde então, houve avanços significativos na instrumentação e nos métodos de auscultação de barragens. Este trabalho tem como objetivo apresentar uma abordagem teórica sobre aspectos técnico-científicos de barragens no Brasil, fundamentada numa revisão de literatura no estado da arte, envolvendo auscultação de barragens no contexto de normas, conceitos, instrumentação, segurança, procedimentos e métodos de monitoramento.Uminho -Universidade do Minho(undefined

Environmental Geodesy: state of the art

With ever increasing global population, intense pressure is being exerted on the Earth’s resources leading to severe changes in its land cover (e. g., deforestation), diminishing biodiversity and natural habitats, dwindling freshwater supplies, and changing weather and climatic patterns (e. g., global warming, changing sea level). Environmental monitoring techniques that provide such information are under scrutiny from an increasingly environmentally conscious society that demands the efficient delivery of such information at a minimal cost. Environmental changes vary both spatially and temporally, thereby putting pressure on traditional methods of data acquisition, some of which are very labour intensive, such as animal tracking for conservation purposes. With these challenges, conventional monitoring techniques, particularly those that record spatial changes call for more sophisticated approaches that deliver the necessary information at an affordable cost. One direction being followed in the development of such techniques involves Environmental Geodesy, which can act as stand-alone method, or to complement traditional methods. This contribution looks at its current state of the art

Application of GNSS-RTK derived topographical maps for rapid environmental monitoring: a case study of Jack Finnery Lake (Perth, Australia)

In environmental monitoring, environmental impact assessments and environmental audits, topographical maps play an essential role in providing a means by which the locations of sampling sites may be selected, in assisting with the interpretation of physical features, and in indicating the impact or potential impact on an area due to changes in the system being monitored (e.g. spatially changing features such as wetlands). Global Navigation Satellite Systems (GNSS) are hereby presented as a rapid method for monitoring spatial changes to support environmental monitoring decisions and policies. To validate the GNSS based method, a comparison is made of results from a small-scale topographic survey using radio based real-time kinematic GNSS (GNSS-RTK) and total station survey methods at Jack Finnery Lake, Perth, Australia.The accuracies achieved by the total station in this study were 2 cm horizontally and 6 cm vertically, while the GNSS-RTKalso achieved an accuracy of 2 cm horizontally, but only 28 cm vertically. While the GNSS-RTK measurements were less accurate in the height component compared to those from the total station method, it is still capable of achieving accuracies sufficient for a topographic map at ascale of 1:1,750 that could support environmental monitoring tasks such as identifying spatial changes in small water bodies or wetlands. The time taken to perform the survey using GNSSRTK, however, was much shorter compared to the total station method, thereby making it quite suitable for monitoring spatial changes within an environmental context, e.g., dynamic mining activities that require rapid surveys and the updating of the monitored data at regular intervals

Earth Observations for Geohazards: Present and Future Challenges

Earth Observations (EO) encompasses different types of sensors (e.g., Synthetic Aperture Radar, Laser Imaging Detection and Ranging, Optical and multispectral) and platforms (e.g., satellites, aircraft, and Unmanned Aerial Vehicles) and enables us to monitor and model geohazards over regions at different scales in which ground observations may not be possible due to physical and/or political constraints. EO can provide high spatial, temporal and spectral resolution, stereo-mapping and all-weather-imaging capabilities, but not by a single satellite at a time. Improved satellite and sensor technologies, increased frequency of satellite measurements, and easier access and interpretation of EO data have all contributed to the increased demand for satellite EO data. EO, combined with complementary terrestrial observations and with physical models, have been widely used to monitor geohazards, revolutionizing our understanding of how the Earth system works. This Special Issue presents a collection of scientific contributions focusing on innovative EO methods and applications for monitoring and modeling geohazards, consisting of four Sections: (1) earthquake hazards; (2) landslide hazards; (3) land subsidence hazards; and (4) new EO techniques and services.Part of this work was supported by the UK Natural Environmental Research Council (NERC) through the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET, ref.: come30001) and the LICS and CEDRRIC projects (refs. NE/K010794/1 and NE/N012151/1, respectively), European Space Agency through the ESA-MOST DRAGON-4 projects (ref. 32244) and the Spanish Ministry of Economy and Competitiveness and EU FEDER funds under projects TIN2014-55413- C2-2-P and ESP2013-47780-C2-2-R

Das Verfahren des GNSS Precise Point Positioning unter Anwendung des Äquivalenzprinzips

In the last decade Precise Point Positioning (PPP) has become a powerful and widely used technique for positioning by means of Global Navigation Satellite System (GNSS) in geodetic/scientific and civil/daily applications. Meanwhile, the equivalence principle of GNSS data processing has been developed and can now be easily explained and accepted since it was firstly algebraically pointed out in 2002. The objective of this thesis is to explore high-performance PPP algorithms and to develop GNSS algorithms with application of the equivalence principle. The core research and contributions of this thesis are summarized as follows. In this thesis it is the first time that the specific equivalence of un-differenced and time differencing PPP algorithms is proved theoretically on the basis of the equivalence principle and the equivalence property of un-differenced and differencing algorithms. Meanwhile, as a supplement to the equivalence property of the triple differences, an alternative method is proposed and derived to prove the equivalence between triple differences and zero-difference which up to now was missing. As a consequence of above conducted theoretical study, a time differencing PPP algorithm based on the equivalence principle is derived and can be used to obtain the coordinates difference and average velocity between two adjacent epochs. Such a time differencing PPP algorithm is able to provide both position and velocity results from the phase and code observations and is expected to be beneficial for applications, such as airborne gravimetry or earthquake monitoring, and could also be an efficient method to detect cycle slips in data processing. The influence of tropospheric delay on PPP, especially in the context of observations in the polar region or with low elevation cut-off angles, where the position results of the observations are more significantly affected by tropospheric delay, is analyzed and a methodology for minimizing its effect is proposed. Actual meteorological data are used and proved to be beneficial for improving PPP precision in the Antarctic region. The effect of tropospheric horizontal gradient correction on PPP is also analyzed and verified to remarkably improve PPP precision under lower elevation cut-off angles and higher humidity conditions. A priori constrained PPP algorithms are proposed and derived in this thesis to improve the efficiency and precision of PPP. The a priori information concerning the geometric and physical properties of observations, which is known with a certain a priori precision, is applied in the PPP algorithms. The contribution of different a priori information constraints on different parameters to PPP solution is analyzed and validated. The a priori constraints as employed in the PPP are specified according to coordinates-, receiver clock offset-, tropospheric delay- and ambiguities-constraints, respectively. The validation of the derived PPP algorithms shows a significant improvement concerning convergence time and positioning accuracy. Moreover, the applications of different constraints under specific conditions are discussed and validated. A multi-constellation combined PPP algorithm based on the equivalence principle is proposed and derived in this thesis. With such an algorithm, the exponentially increased computational load of the traditional multi-GNSS PPP algorithm can be reduced to the single linear increase when more GNSS satellites are available and used for combined computation. In case of GPS/BDS combination, a method which can speed up the determination of the ambiguities parameters of BDS through applying the contribution of GPS observations is proposed to significantly reduce the convergence time in BDS PPP. The GPS/BDS combined PPP algorithm with inter-system bias (ISB) parameter is also derived. Using the estimated ISB as a priori constraint in the GPS/BDS combined PPP is proposed. The result demonstrates that the a priori constraint of ISB shows superiority in the convergence time of PPP processing and can mainly improve the positioning accuracy in E component. In traditional combined PPP it is difficult to adaptively adjust the contribution of each single system to the combination through constructing total calculation, and it will lead to the deterioration in the combination accuracy. In this context, the adaptively combined PPP algorithms based on the equivalence principle are proposed and derived, which can easily achieve an adaptive adjustment of weight ratio of each system in the multi-GNSS combination. By using the posteriori covariance matrix of the shared parameters of each single system and the Helmert variance components to adaptively adjust the weight ratio of each system, the derived algorithms can improve the accuracy of combination significantly, compared to combined PPP with identical weight ratio. The developed algorithms are net applicable and can be used for cloud computation for internet GNSS service which is considered relevant for possible commercial applications.In den letzten zehn Jahren entwickelte sich das Verfahren des Precise Point Positioning (PPP) zu einer leistungsstarken und weit verbreiteten Technik in der Positionsbestimmung mittels des Global Navigation Satellite System (GNSS) in geodätischen/wissenschaftlichen und zivilen/täglichen Anwendungen. Ein wichtiges Grundprinzip der GNSS-Datenverarbeitung ist das Äquivalenzprinzip der GNSS-Datenverarbeitung, das 2002 erstmals beschrieben wurde. Das Ziel dieser Arbeit ist die Untersuchung von Hochleistungs-PPP-Algorithmen und die Entwicklung von GNSS-Algorithmen unter Anwendung des Äquivalenzprinzips. Der Kern der Untersuchungen und die Beiträge dieser Arbeit lassen sich wie folgt zusammengefassen. Aufbauend auf dem Äquivalenzprinzip und den Äquivalenz-Eigenschaften von nicht-differenzierenden und differenzierenden GNSS-Algorithmen wird in dieser Arbeit zum ersten Mal die spezifische Gleichwertigkeit von nicht-differenzierenden und zeitdifferenzierenden PPP-Algorithmen theoretisch bewiesen. In diesem Zusammenhang beschreiben wir – als Ergänzung zu den Äquivalenz-Eigenschaften der Tripel-Differenzen - eine bis jetzt noch nicht existierende alternative Methode zum Beweis der Äquivalenz von Tripel-Differenzen und undifferenzierten Beobachtungen. Aufbauend auf der oben erwähnten theoretischen Untersuchung wurde ein zeitlich differenzierender PPP-Algorithmus abgeleitet, der auf dem Äquivalenzprinzip beruht und der dazu benutzt werden kann, die Koordinatendifferenz und die mittlere Geschwindigkeit zwischen benachbarten Beobachtungszeitpunkten zu bestimmen. Ein solcher zeitlich differenzierender PPP-Algorithmus ist in der Lage, sowohl Position als auch Geschwindigkeit aus Phasen- und Code-Beobachtungen zu liefern. Dieser Algorithmus sollte für Anwendungen wie Fluggravimetrie oder Erdbeben-Überwachung nützlich sein und stellt eine effiziente Methode zur Erkennung von Cycle-Slips dar. Diese Arbeit umfasst auch Analysen des Einflusses der Troposphärischen Signalverzögerung auf das PPP, vor allem im Blick mit Beobachtungen in den Polarregionen oder im Fall niedriger Höhengrenzwinkel (sog. Cut-off-Winkel), wo die Positionsbestimmung sehr stark von der Troposphärischen Signalverzögerung beeinflusst ist. In diesem Zusammenhang wird eine Methodologie zur Minimierung des Troposphäreneinflusses vorgeschlagen. Es werden reale meteorologische Daten verwendet und es wird gezeigt, dass dies zur Verbesserung der Präzision des PPP in antarktischen Regionen von Vorteil ist. Außerdem wird der Effekt der troposphärischen Horizontalgradienten-Korrektur analysiert und es wurde bewiesen, dass diese Methode zu einer deutlichen Verbesserung des PPP im Fall niedriger Cut-off-Winkel und hoher Luftfeuchtigkeit führt. In dieser Arbeit werden PPP-Algorithmen mit A-priori-Nebenbedingungen (sog. Constraint) vorgeschlagen und abgeleitet, um die Effizienz und Präzision des PPP zu verbessern. Die in den PPP-Algorithmen angewandten A-priori-Informationen betreffen die geometrischen und physikalischen Eigenschaften von Beobachtungen, von denen vorab eine bestimmte Genauigkeit bekannt ist. Der Einfluss von verschiedenen A-priori-Nebenbedingungen auf verschiedene Parameter innerhalb der PPP-Lösung wird analysiert und validiert. Diese in den PPP-Algorithmen angewandten A-priori-Bedingungen sind aus Nebenbedingungen für Koordinaten, Empängeruhren-Offsets, Troposphären-Verzögerung und Ambiguities abgeleitet. Die Validierung dieser Algorithmen zeigt eine deutliche Verbesserung bezüglich der Konvergenzzeit und der Genauigkeit in der Positionsbestimmung. Ferner wird die Anwendung verschiedener Constraints unter spezifischen Bedingungen diskutiert unf validiert. In dieser Arbeit wurde ein kombinierter PPP-Algorithmus für Multi-Satellitensysteme vorgeschlagen und abgeleitet, der auf dem genannten Äquivalenzprinzip beruht. Mit einem solchen Algorithmus kann die exponentiell ansteigende Computerlast des traditionellen Multi-GNSS-PPP dahingehend reduziert werden, dass es nur einen einfachen linearen Anstieg gibt, wenn mehr GNSS-Satelliten einbezogen werden. Für den Fall der Kombination von GPS mit dem chinesischen Beidou-System (BDS) wird eine Methode vorgeschlagen, die die Berechnung der Ambiguity-Parameter für das BDS-System durch Beitrag von GPS-Beobachtungen schneller beschleunigt. Diese Methode reduziert die Konvergenzzeit im BDS-PPP deutlich. Außerdem wird im Fall der Kombination von GPS und BDS ein Inter-System-Bias (ISB) abgeleitet. Es wird vorgeschlagen, diesen ISB als A-priori-Nebenbedingung in das PPP bei der Kombination von GPS und BDS einzuführen. Dadurch ergeben sich überlegene Resultate für die Konvergenzzeit in der PPP-Prozessierung und die Positionsgenauigkeit in der Ost-Komponente kann verbessert werden. Im traditionellen kombinierten PPP-Verfahren ist es schwierig, den Beitrag jedes einzelnen Systems zur Kombination durch Konstruktion einer Gesamtlösung adaptiv anzugleichen, was zur Verschlechterung in der Kombinationsgenauigkeit führt. In diesem Zusammenhang wurde ein adaptiv kombinierter PPP-Algorithmus vorgeschlagen und entwickelt, der auf dem Äquivalenzprinzip beruht. Dieser Algorithmus ermöglicht eine einfache adaptive Ausgleichung der relativen Wichtungen für jedes Satelliten-System in der Multi-GNSS-Kombination. Durch Nutzung der a-posteriori Kovarianz-Matrix, die für alle gemeinsamen Parameter der einzelnen Satelliten-Systeme aufgestellt wurde und durch die Anwendung der Helmertschen Varianzkomponenten-Schätzung zur adaptiven Ausgleichung der relativen Wichtungen der einzelnen Systeme kann die Genauigkeit der Kombination im Vergleich zum PPP mit identischen Relativgewichten deutlich gesteigert werden. Die entwickelten Algorithmen sind über das Internet anwendbar und könnten für Cloud-Berechnungen im Rahmen eines Internet-GNSS-Dienstes verwendet werden, was für mögliche kommerzielle Anwendungen von Bedeutung sein könnte

Small unmanned airborne systems to support oil and gas pipeline monitoring and mapping

Acknowledgments We thank Johan Havelaar, Aeryon Labs Inc., AeronVironment Inc. and Aeronautics Inc. for kindly permitting the use of materials in Fig. 1.Peer reviewedPublisher PD