The atmosphere in low latitude regions is of particular interest to GPS researchers because the propagation of GPS signals becomes significantly delayed compared with other regions of the world. Hence this limits GPS positioning accuracy in equatorial regions. Although the atmospheric delay can be modelled, a residual component will still remain. Reducing, or mitigating the effect of residual atmospheric delay is of great interest, and remains a challenge, especially in equatorial regions. Analysis of relative positioning accuracy of GPS baselines has confirmed that the residual atmospheric delay is distance-dependent, even in low latitude areas. Residual ionospheric delay is the largest component in terms of both absolute magnitude and variability. However it can be largely eliminated by forming the ionosphere-free combination of measurements made on two frequencies. The residual tropospheric delay is smaller in magnitude but rather problematic due to strong spatio-temporal variations of its wet component. Introducing additional troposphere ???scale factors??? in the least squares estimation of relative position can reduce the effect of the residual. In a local GPS network, the distance-dependent errors can be spatially modelled by network-based positioning. The network-based technique generates a network ???correction??? for user positioning. The strategy is to partition this network correction into dispersive and non-dispersive components. The latter can be smoothed in order to enhance the ionosphere-free combination, and can be of benefit to ambiguity resolution. After this step, both the dispersive and non-dispersive correction components can be used in the final positioning step. Additional investigations are conducted for stochastic modelling of network-based positioning. Based on the least squares residuals, the variance-covariance estimation technique can be adapted to static network-based positioning. Moreover, a two-step procedure can be employed to deal with the temporal correlation in the measurements. Test results on GPS networks in low latitude and mid-latitude areas have demonstrated that the proposed network-based positioning strategy works reasonably well in resolving the ambiguities, assisting the ambiguity validation process and in computing the user???s position. Furthermore, test results of stochastic modelling in various GPS networks suggests that there are improvements in validating the ambiguity resolution results and handling the temporal correlation, although the positioning result do not differ compared to using the simple stochastic model typically used in standard baseline processing.

Diss. phil-nat. Bern, 1999.

Stuttgart, Univ., Studienarb., 2003.

Thèse (M.Sc.)--Université Laval, 1998. / Bibliogr.: f. [111]-116. Publié aussi en version électronique.

This work explicates a simple GPS receiver intended for laboratory demonsration of DSSS signal demodulation and apparent distance measurement. The receiver will be able to seek for individual sattelite signals, measure their shift against local oscillator, demodulate navigational data, display information on LCD and communicate with PC via USB.

No description available.

Since its introduction in the early 1980??s, the Global Positioning System (GPS) has become an important worldwide resource. Although the primary use of GPS is for position location, the inherent timing accuracy built into the system has allowed it become an important synchronisation resource for other systems. In most cases the GPS end user only requires a position estimate without awareness of the timing and synchronisation aspects of the system. A low accuracy position (at the several-metre level) with a low update rate of about 1Hz is often acceptable. However, obtaining more accurate position estimates (at the sub-metre level) at higher update rates requires the use of differential correction signals (DGPS) and greater processing power in the receiver. Furthermore, some extra challenges arise when simultaneously gathering information from a group of independently moving remote GPS receivers (rovers) at increased sampling rates (10Hz). This creates the need for a high bandwidth telemetry system and techniques to synchronise the position measurements for tracking each rover. This thesis investigates and develops an overall solution to these problems using GPS for both position location and synchronisation. A system is designed to generate relative position information from 30 or more rovers in real-time. The important contributions of this research are as follows: a) A GPS synchronised telemetry system is developed to transport GPS data from each rover. Proof of concept experiments show why a conventional RF Local Area Network (LAN) is not suitable for this application. The new telemetry system is developed using Field Programmable Gate Array (FPGA) devices to embed both the synchronising logic and the central processor. b) A new system architecture is developed to reduce the processing load of the GPS receiver. Furthermore, the need to transfer the DGPS correction data to the rover is eliminated. Instead, the receiver raw data is processed in a centralised Kalman filter to produce multiple position estimates in real-time. c) Steps are taken to optimise the telemetry data stream by using only the bare essential data from each rover. A custom protocol is developed to deliver the GPS receiver raw data to the central point with minimal latency. The central software is designed to extract and manage common elements such as satellite ephemeris data from the central reference receiver only. d) Methods are developed to make the overall system more robust by identifying and understanding the points of failure, providing fallback options to allow recovery with minimal impact. Based on the above a system is designed and integrated using a mixture of custom hardware, custom software and off-the-shelf hardware. Overall tests show that efforts to minimise latency, minimise power requirements and improve reliability have delivered good results.

GPS technologijai tapus prieinama ne tik karinei pramonei buvo pradėtos kurti įvairios paskirties pozicionavimo sistemos, skirtos eiliniams IT vartotojams. To pasėkoje atsirado naujo pobūdžio paslaugų rūšis – paslaugos pagrįstos vartotojo pozicijos nustatymu. Darbe išanalizuotos plačiai taikomos pozicionavimo sistemos ir išskirtas pagrindinis tokių sistemų funkcionalumas, palygintos pozicionavimo technologijos, jų privalumai ir trūkumai viena kitos atžvilgiu. Darbe aprašomas projektinis sprendimas, panaudotas kuriant daugiavartotojišką pozicionavimo sistemą, kurios architektūra ir svarbiausi realizacijos aspektai pateikiami šiame darbe. Išskirtos dažnai praktikoje pasitaikančios paskirstytų sistemų projektavimo, realizavimo ir testavimo klaidos, dėl kurių gali nepavykti sėkmingai ir laiku įgyvendinti projektą arba kritinės sistemos dalys gali būti netinkamos naudoti realiuose įrenginiuose. Pasiūlytas būdas, kaip išvengti tokių klaidų ir sumažinti riziką, kad projektas gali nepavykti. Eksperimento metu įrodyta, jog paskirstytų sistemų klientų, skirtų mobiliems įrenginiams (mobiliems telefonams ir PDA), kūrimo ir testavimo procesas neturi apsiriboti vien tik emuliatoriais, kuriuose vykdomos programos elgesys ir charakteristikos gali labai skirtis nuo realiame įrenginyje vykdomos programos. / Many different positioning systems for ordinary IT users were developed since GPS technology became available not only to US military. Those systems led to new kind of services – location-based services. Some of the widely used positioning systems are analyzed in this work and their main functionality is marked out, positioning technologies compared. Architecture of multi-user positioning system and its main implementations aspects are given. Also there is an analysis of distributed system development and testing issues that may lead to project failure or its cost rising and a software development and testing model suggested. This is a practical model which lets reduce the risk of failure.

Since its introduction in the early 1980??s, the Global Positioning System (GPS) has become an important worldwide resource. Although the primary use of GPS is for position location, the inherent timing accuracy built into the system has allowed it become an important synchronisation resource for other systems. In most cases the GPS end user only requires a position estimate without awareness of the timing and synchronisation aspects of the system. A low accuracy position (at the several-metre level) with a low update rate of about 1Hz is often acceptable. However, obtaining more accurate position estimates (at the sub-metre level) at higher update rates requires the use of differential correction signals (DGPS) and greater processing power in the receiver. Furthermore, some extra challenges arise when simultaneously gathering information from a group of independently moving remote GPS receivers (rovers) at increased sampling rates (10Hz). This creates the need for a high bandwidth telemetry system and techniques to synchronise the position measurements for tracking each rover. This thesis investigates and develops an overall solution to these problems using GPS for both position location and synchronisation. A system is designed to generate relative position information from 30 or more rovers in real-time. The important contributions of this research are as follows: a) A GPS synchronised telemetry system is developed to transport GPS data from each rover. Proof of concept experiments show why a conventional RF Local Area Network (LAN) is not suitable for this application. The new telemetry system is developed using Field Programmable Gate Array (FPGA) devices to embed both the synchronising logic and the central processor. b) A new system architecture is developed to reduce the processing load of the GPS receiver. Furthermore, the need to transfer the DGPS correction data to the rover is eliminated. Instead, the receiver raw data is processed in a centralised Kalman filter to produce multiple position estimates in real-time. c) Steps are taken to optimise the telemetry data stream by using only the bare essential data from each rover. A custom protocol is developed to deliver the GPS receiver raw data to the central point with minimal latency. The central software is designed to extract and manage common elements such as satellite ephemeris data from the central reference receiver only. d) Methods are developed to make the overall system more robust by identifying and understanding the points of failure, providing fallback options to allow recovery with minimal impact. Based on the above a system is designed and integrated using a mixture of custom hardware, custom software and off-the-shelf hardware. Overall tests show that efforts to minimise latency, minimise power requirements and improve reliability have delivered good results.

Ce travail vise à mieux comprendre les interactions entre couplage, glissement lent et rupture sismique en contexte de subduction. L’objet d’étude est la subduction Nord Chili–Sud Pérou, qui a été reconnue comme une lacune sismique et qui a fait l’objet d’un important effort international d’instrumentation géophysique. Cette zone a été affectée par tremblements de terre qui ont été bien enregistrés, ce qui en fait une cible bien adaptée pour étudier les mécanismes de préparation des grands séismes de subduction, et le lien entre couplage, glissements lents et rupture sismique.Les 65 stations GPS installées dans la zone ont été traitées en doubles différences avec le logiciel GAMIT-GLOBK sur la période 2000-2014. Les séries temporelles de position obtenues ont été analysées et les déplacements associés aux différentes phases du cycle sismique et aux mouvements saisonniers ont été modélisés.L’analyse des tendances dans les séries temporelles GPS ont permis de mettre en évidence un changement de vitesse intersismique avant et après le séisme en slab-pull de Tarapacà de juin 2005, dans la région qui a été rompue par le séisme d’interface d’Iquique en 2014. Ce changement de vitesse est associé à un changement de taux de sismicité superficielle et profonde. Le déclustering du catalogue sismique indique que ce changement de taux, affecte aussi la sismicité de fond, caractéristique du taux de chargement. Nous avons pu mettre en évidence que des interactions existent entre sismicité profonde et superficielle, et pourraient jouer un rôle important dans la préparation des grands séismes d’interface. A plus courte échelle de temps, les séries temporelles montre un autre changement de vitesse 8 mois avant le séisme d’Iquique. La modélisation indique que ce changement correspond à un glissement lent de Mw 6.5, essentiellement asismique, correspondant à la phase de nucléation long-terme de ce tremblement de terre.Nous avons également analysé les variations court terme dans les signaux non-modélisés des séries temporelles GPS, qui ont permis d’identifier, grâce à une méthode de Template Matching 48 petits événements de glissement lent pendant la période de chargement intersismique. Ces événements sont basés pour leur grande majorité en dessous de la zone sismogénique dans des zones de couplage très faible, ou de couplage intermédiaire, indiquant que le glissement se fait par relâchements successifs. Souvent ces événements transitoires sont corrélés à des pics d’activité sismique, notamment profonde.La cinématique de la source du séisme d’Iquique et de sa plus grosse réplique a été étudiée en combinant données GPS à haute fréquence et données accélérométriques. Les déplacements statiques ont été inversés pour caractériser la répartition du moment géométrique. Cette source statique a ensuite été utilisée comme prior pour une séquence d’inversions cinématiques en fréquence. Les résultats montre que ces deux séismes présentent une distribution de glissement bimodale, segmentée selon la profondeur. L’extension latérale du choc principal correspond à celle d’un bassin submergé d’avant arc associé à une anomalie de gravité, et pourrait être contrôlée par les structures tectoniques de la croûte supérieure. La réplique principale est située dans une zone de changement de contrainte de Coulomb induit par le choc principal, ce qui suggère qu’elle a été déclenchée par celui ci.Grâce à une combinaison de données géodésiques et sismologiques, ce travail offre donc une vue détaillée des processus en jeu au cours du séisme d’Iquique et des décades qui l’ont précédé. Les perspectives de recherches soulevées par ce travail sont nombreuses, notamment sur les possibilités d’observations raffinées des phénomènes associés au cycle sismique et à la préparation des grands tremblements de terre de subduction. / The aim of this Ph.D. thesis is to have a better comprehension of the interactions between coupling, slow slip events (SSEs) and the seismic ruptures in subduction zones. This work focuses on the North Chile - South Peru subduction zone that has been recognized as a mature seismic gap. Thus, the region has been the target of an important international effort in geophysical instrumentation (GPS and seismological stations), since the mid-2000s. The region has been affected by several well-registered earthquakes, that makes it good case to study the earthquake preparation phase and the relationship between coupling, SSE and seismic rupture.The 65 stations available in the region have been processed in double differences using the GAMIT-GLOBK software in the period 2000-2014. The GPS displacement time series have been analyzed and the associated displacements to the different stages of the seismic cycle as well as seasonal signals have been modeled.The analysis of the tendencies in the GPS time-series evidences a change in the velocity field before and after the Tarapaca slab-pull earthquake occurrence in June 2005, in the range of latitude affected by Iquique earthquake in 2014. This velocity change is associated with a change in the shallow and deep seismicity rates. The analysis of the declustered catalog shows that the velocity change observed affects the background seismicity as well, that often seen as a proxy for the tectonic loading. Finally, we find interactions between shallow and deep seismicity, that may play an important role in the interface earthquakes preparation phase. At a shorter time scale, the time series show another change in velocity 8 months before Iquique earthquake. Models indicate that the velocity change corresponds to an SSE Mw 6.5, mainly aseismic, corresponding to the long preparation phase of the earthquake.The short-term GPS velocity variations have also been analyzed on residual signal. It allows identifying, thanks to a matched-filter, 48 small SSEs during the interseismic period. These events are localized mostly in the deeper part of the seismogenic zone, in areas where the coupling is low or with intermediate values. It suggests that the slip in these regions is produced in burst way. Some of those events are correlated with peaks of seismic activity, especially at intermediate depths.Finally, the kinematic rupture process of Iquique earthquake process and its biggest aftershock are studied, employing a combination of high-rate GPS and strong motion data. The static displacements are inverted to characterize the slip. This static solution is used as apriori information for a sequence of kinematic inversions in the frequency domain. The results show that both events have a bimodal slip distribution, segmented along dip. The lateral extension of the mainshock is centered on a forearc offshore basin associated with a gravity anomaly, and may be controlled by tectonic structures of the upper crust. The aftershock is located in an area with strong Coulomb Stress Changes induced by the mainshock, suggesting that it was triggered by the mainshock.Thanks to the combination of geodetic and seismological data, this thesis provides a detailed vision of the processes involved during the Iquique earthquake and the previous decades. The research prospects raised by this work are numerous, particularly on the possibilities of refined observations of the phenomena associated with the seismic cycle and the preparation of large subduction earthquakes.