Time Reference System Research Articles

On the analysis-readiness of spatio-temporal Earth data and suggestions for its enhancement

Data about the Earth, like in many other domains, are too difficult to access. In order to perform some insight-gaining task a series of steps has to be performed which often require a spectrum of detail technology skills which are not related to the original Earth science task on hand. Special-purpose file formats with sometimes rather peculiar mechanics, juggling with horizontal, vertical, and time reference systems, and scaling up processing to large amounts of data are just a few of such common issues. One reason is that data often are provided in a more generator-centric (where generator can be a sensor or a program, such a weather forecast) than user-centric manner, which might be called “too upstream”.As is well-known, this hinders EO exploitation significantly, making such tasks impossible to conquer for non-experts and tedious for experts. For the desirable, user-friendly opposite the term Analysis-Ready Data (ARD) has been coined by the USGS Landsat team and has gone viral since.However, despite significant work, such as in CEOS, and visible progress – ultimately it is by no means clear what ARD exactly means and how it can be achieved.In this paper, we take a fresh look focusing on spatio-temporal raster data, i.e., datacubes, modeled as coverages according to the authoritative OGC and ISO standards. The Holy Grail of this study is automatic data fusion of Earth data. Based on long-term own practice (and suffering) we list shortcomings and propose ways forward, including research and standardization directions.

Clock Ensemble Algorithm Test in the Establishment of Space-Based Time Reference

A new concept of a space-based synchronized reference network is proposed with the development of an optical frequency reference and laser inter-satellite link. To build such time reference, three clock ensemble algorithms, namely the natural Kalman timescale (NKT) algorithm, the reduced Kalman timescale (RKT) algorithm, and the two-stage Kalman timescale (TKT) algorithm are considered. This study analyzes and compares the performance of these algorithms using BDS, GPS, and Galileo satellite clock data from the GFZ GNSS clock corrections, which will be used in constructing future space-based time references. The study shows that the NKT algorithm improves frequency stability by 0.1–0.2 orders of magnitude in the short and medium term. When the satellite clock is mostly a hydrogen clock, the RKT and NKT are close, and the short and medium-term frequency stability slightly increases. In contrast, the TKT algorithm produces a timescale that improves frequency stability by 1–3 orders of magnitude. A quadratic polynomial model predicts the three timescales, with the results indicating that the short-term prediction accuracy of the satellite clock is within 1ns, and the TKT algorithm’s prediction accuracy is 1–2 orders of magnitude higher than that of the NKT and RKT algorithms. With the deployment of next-generation Low Earth Orbit (LEO) satellites equipped with higher-precision clocks, the space-based time reference system will achieve improved accuracy and greater potential for practical applications.

GENESIS: co-location of geodetic techniques in space

Improving and homogenizing time and space reference systems on Earth and, more specifically, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1 mm and a long-term stability of 0.1 mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, such as those located at tide gauges, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation, contributing to a better understanding of natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities, including the International Association of Geodesy (IAG), which has enunciated geodesy requirements for Earth sciences. Moreover, the United Nations Resolution 69/266 states that the full societal benefits in developing satellite missions for positioning and Remote Sensing of the Earth are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology. This paper has been written and supported by a large community of scientists from many countries and working in several different fields of science, ranging from geophysics and geodesy to time and frequency metrology, navigation and positioning. As it is explained throughout this paper, there is a very high scientific consensus that the GENESIS mission would deliver exemplary science and societal benefits across a multidisciplinary range of Navigation and Earth sciences applications, constituting a global infrastructure that is internationally agreed to be strongly desirable.Graphical

ONCLE (One Clock Ensemble) for Galileo’s Next-Generation Robust Timing System

<h3>Abstract</h3> This paper presents the ONCLE (One Clock Ensemble) solution for the Galileo time and frequency reference system with advanced features in terms of robustness, performance, continuity, and simplicity. Each component clock is frequency-steered to the ensemble time, which itself creates an average of those steered clock outputs, while clock faults are detected and corrected in real time within an integrated system. The feasibility of algorithm and hardware approaches has been demonstrated on an elegant breadboard and verified by an extended test and validation campaign at the Engineering Model (EM) level, developed for the Galileo next-generation onboard timing system under European GNSS Evolutions Program. Based on the progress for space application and the heritage on the Galileo ground precise timing facility (PTF), we propose a robust solution for the upgrade of PTF for ground application aiming to provide a fully continuous and performance-improved timescale under automated operation. The capability is demonstrated by preliminary simulation results.

Geomagnetic Effects of Remote Earthquakes

The paper presents the results of a study of the relationship of seismic events with geomagnetic disturbances arising from the acoustic impact on the lower ionosphere, which are caused by vibrations of the Earth’s surface at distances of several thousand kilometers from the earthquake source. The measurements were carried out at Mikhnevo Observatory, which is equipped with an instrumental complex, including seismic, acoustic, electromagnetic, and ionospheric means of observation. It is also equipped with a time-reference system that uses GPS receivers, which ensures an accuracy of the measurement data synchronization of no worse than 20 ns. The regularities of the formation of atmospheric and geomagnetic effects of distant earthquakes and the dependence of the time of their occurrence on the distance to the seismic source are shown on the example of five seismic events. It is demonstrated that the difference in the nature and time of the occurrence of geomagnetic pulsations associated with the impact of acoustic waves on the ionosphere differ from the signals caused by the seismomagnetic effect.

Reference Systems in the Navigation of Moving Objects

It is shown that with uniform and rectilinear motion of two, three or several free inert bodies in one-dimensional or three-dimensional space, arbitrary inertial reference systems, including those associated with each of the moving inert bodies, are not substantially equivalent in part of the total kinetic energy. In the particular case, if two free inert bodies with masses m 1 and m 2 move relative to each other with a constant velocity v, then in the inertial reference system associated with the first body, the total kinetic energy of the bodies is equal to E 112 . In the inertial reference frame associated with the second body, the total kinetic energy of the bodies is equal to E 212 . In an arbitrary (third) inertial reference frame, the first inert body moves at a speed v 1 , the second at a speed v 2 . In the third reference system, the total kinetic energy is E 312 . In terms of kinetic energy, all three inertial reference systems are not substantially equivalent. At the same time, none of these reference systems is unique or distinguished. If it is necessary to choose a unique or dedicated inertial reference system, one can proceed from the condition of the minimum of the total kinetic energy of moving inert bodies in this system. At the same time, a unique or distinguished inertial reference system is a relic reference system associated with the center of mass of moving inert bodies and with the epicenter of their initial hypothetical interaction. Relic reference systems are calculated. Inert bodies do not necessarily interact with them initially. The use of relic reference systems allows you to maintain a balance between kinetic energy and the work performed. The number of inert bodies in the calculation of the relic reference system can be arbitrarily large. If the theory of the Big Bang is true, then the world relic inertial reference system is connected with its epicenter, which is the center of mass of the universe.

In-beam test of the RPC architecture foreseen to be used for the CBM-TOF inner wall

The Time Of Flight (TOF) subsystem is one of the main detectors of the CBM experiment. The TOF wall in conjunction with Silicon Tracking System (STS) is foreseen to identify charged hadrons, i.e. pions, kaons and protons, with a full azimuthal coverage at 2.50 - 250 polar angles. A system time resolution of at least 80 ps, including all contributions, such as electronics jitter and the resolution of the time reference system, is required. Such a performance should be maintained up to a counting rate larger than 30 kHz/cm2 at the most inner region of TOF wall.Our R&D activity has been focused on the development of two-dimensional position sensitive Multi-gap Resistive Plate Counter (MRPC) prototypes for the forward region of the CBM-TOF subdetector, the most demanding zone in terms of granularity and counting rate.The in-beam tests using secondary particles produced in 30 GeV/u Pb ion collisions on a Pb target at SPS - CERN aimed to test the performance of these prototypes in conditions similar to the ones expected at SIS100 at FAIR. The performance of the prototypes is studied in conditions of exposure of the whole active area of the chamber to high multiplicity of reaction products.The results show that this type of MRPC fulfill the challenging requirements of the CBM-TOF wall. Therefore, such an architecture is recommended as basic solution for CBM-TOF inner zone.

Development of a toolbox to dissect host-endosymbiont interactions and protein trafficking in the trypanosomatid Angomonas deanei.

BackgroundBacterial endosymbionts are found across the eukaryotic kingdom and profoundly impacted eukaryote evolution. In many endosymbiotic associations with vertically inherited symbionts, highly complementary metabolic functions encoded by host and endosymbiont genomes indicate integration of metabolic processes between the partner organisms. While endosymbionts were initially expected to exchange only metabolites with their hosts, recent evidence has demonstrated that also host-encoded proteins can be targeted to the bacterial symbionts in various endosymbiotic systems. These proteins seem to participate in regulating symbiont growth and physiology. However, mechanisms required for protein targeting and the specific endosymbiont targets of these trafficked proteins are currently unexplored owing to a lack of molecular tools that enable functional studies of endosymbiotic systems.ResultsHere we show that the trypanosomatid Angomonas deanei, which harbors a β-proteobacterial endosymbiont, is readily amenable to genetic manipulation. Its rapid growth, availability of full genome and transcriptome sequences, ease of transfection, and high frequency of homologous recombination have allowed us to stably integrate transgenes into the A. deanei nuclear genome, efficiently generate null mutants, and elucidate protein localization by heterologous expression of a fluorescent protein fused to various putative targeting signals. Combining these novel tools with proteomic analysis was key for demonstrating the routing of a host-encoded protein to the endosymbiont, suggesting the existence of a specific endosymbiont-sorting machinery in A. deanei.ConclusionsAfter previous reports from plants, insects, and a cercozoan amoeba we found here that also in A. deanei, i.e. a member of a fourth eukaryotic supergroup, host-encoded proteins can be routed to the bacterial endosymbiont. This finding adds further evidence to our view that the targeting of host proteins is a general strategy of eukaryotes to gain control over and interact with a bacterial endosymbiont. The molecular resources reported here establish A. deanei as a time and cost efficient reference system that allows for a rigorous dissection of host-symbiont interactions that have been, and are still being shaped over evolutionary time. We expect this system to greatly enhance our understanding of the biology of endosymbiosis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0820-z) contains supplementary material, which is available to authorized users.

Data quality assessment and the positioning performance analysis of BeiDou in Hong Kong

As the satellite constellation, frequency structure, time and coordinate reference system of the Chinese BeiDou are all different from those of GPS, the quality of observations is also supposed to be different from GPS. At the same time, the positioning performance of the GPS and BeiDou combined system should be much better in view of the availability of more visible satellites. The purpose of this paper is to assess the quality of BeiDou pseudorange and carrier phase observation, and to compare the performance of GPS, BeiDou and the combined system in terms of availability, integrity and positioning accuracy with practical data in Hong Kong. The experiment results showed that the noise and multipath of GEOs (geostationary earth orbit satellites) pseudorange measurement fluctuates within 1.5 m, while the variations of IGSOs (geostationary earth orbit inclined geosynchronous orbit satellites) and MEOs (medium earth orbit satellites) are more obvious. The amplitudes of the triple-carrier combination of time series of GEOs, IGSOs and MEOs carrier phase measurements are 4, 6, and 6 mm, respectively. In addition, the absolute and relative positioning precision of BeiDou is very similar to that of GPS, and the performance of the combined systems is best.

Relativistic transformations between global and local velocities of an orbiter under IAU Resolutions

Einstein's general relativity (GR) has become an inevitable part of deep space missions. According to the International Astronomical Union (IAU) Resolutions which are built in the framework of GR, several time scales and reference systems are recommended to be used in the solar system for control, navigation and scientific operation of a spacecraft. Under the IAU Resolutions, we derive the transformations between global and local velocities of an arbitrary orbiter. These transformations might be used in orbit determination with Doppler tracking and prediction of Doppler observables for the spacecraft. Taking the YingHuo-1 Mission as a technical example of future Chinese Mars explorations, we evaluate the significance and contributions of various components in the transformations. The largest contribution of the relativistic parts in the transformations can reach the level of ∼ 5 × 10−5 m s−1. This suggests that, for such a spacecraft like we have assumed, if the accuracy of Doppler tracking is better than ∼ 5 × 10−5 m s−1 then the relativistic parts of the transformations of velocities will be required.

Study on GNSS Time Reference System and its Traceability

This paper introduces briefly international standard time scale---theCoordinated Universal Time (UTC) and its realization, the time references and their traceability of Global Navigation Satellite System (GNSS). GNSS is based on precision time measurement, an uniform internal time reference is necessary to ensure all parts in a GNSS run synchronously. All GNSS system have precision time reference systems, at the same time, it is necessary that the time reference should be traced to the international legal time standard, UTC, to ensure global time synchronous and uniform, it can be realized by establishing time comparison link with national time standard. A possible solution of GNSS time reference and its traceability for COMPASS is discussed.

The Compass Time System and its Interoperation

We report on the time reference system of Compass global satellite navigation system and its interoperation with other GNSS’s. China has sent three satellites into geostationary orbit since 2000, and Compass Navigation Test System has been established. Compass time reference, named as BDT, is based on Atomic time, BDT is derived from the atomic clock ensemble in Compass ground control centre, and be traced to the international time, UTC. Interoperability is one of the most important aspect in the design of Compass timing system, a solution of time differences determination among BDT and other GNSS time scales are introduced in this paper.

The Compass and its time reference system

We report on the Compass global satellite navigation system and its time reference system. China has sent three satellites into geostationary orbit since 2000, and the Compass Navigation Test System has been established. Compass time reference, named as BDT, is based on atomic time; BDT is derived from the atomic clock ensemble in Compass ground control centre and can be traced to the international time, UTC.

Global positioning: technologies and performance

Foreword. Acknowledgements. Preface. Chapter 1. A brief history of navigation and positioning. 1.1 The first age of navigation. 1.2 The age of the great navigators. 1.3 Cartography, lighthouses and astronomical positioning. 1.4 The radio age. 1.5 The first terrestrial positioning systems. 1.6 The era of artificial satellites. 1.7 Real-time satellite navigation constellations today. 1.8 Exercises. Bibliography. Chapter 2. A brief explanation of the early techniques of positioning. 2.1 Discovering the world. 2.2 The first age of navigation and the longitude problem. 2.3 The first optical based calculation techniques. 2.4 The first terrestrial radio based systems. 2.5 The first navigation satellite systems: TRANSIT and PARUS/TSIKADA. 2.6 The second generation of navigation satellite systems: GPS, GLONASS and Galileo. 2.7 The forthcoming third generation of navigation satellite systems: QZSS and COMPASS. 2.8 Representing the world. 2.9 Exercises. Bibliography Chapter 3. Development, deployment and current status of satellite based navigation systems. 3.1 Strategic, economical and political aspects. 3.2 The global positioning satellite systems: GPS, GLONASS and Galileo. 3.2.1 The Global Positioning System : GPS. 3.2.2 The GLONASS. 3.2.3 Galileo. 3.3 The GNSS1: EGNOS, WAAS and MSAS. 3.4 The other satellite based systems. 3.5 Differential satellite based commercial services. 3.6 Exercises. Bibliography. Chapter 4. Non-GNSS positioning systems and techniques for outdoors. 4.1 Introduction (large area without contact or wireless systems). 4.2 The optical systems. 4.3 The terrestrial radio systems. 4.4 The satellite radio systems. 4.5 Non-radio based systems. 4.6 Exercises. Bibliography. Chapter 5. GNSS system descriptions. 5.1 System description. 5.2 Summary and comparison of the three systems. 5.3 Basics of GNSS positioning parameters. 5.4 Introduction to error sources. 5.5 Concepts of differential approaches. 5.6 SBAS system description (WAAS and EGNOS). 5.7 Exercises. Bibliography. Chapter 6. GNSS navigation signals: description and details. 6.1 Navigation signal structures and modulations for GPS, GLONASS and Galileo. 6.2 Some explanations of the concepts and details of the codes. 6.3 Mathematical formulation of the signals. 6.4 Summary and comparison of the 3 systems. 6.5 Developments. 6.6 Error sources. 6.7 Time reference systems. 6.8 Exercises. Bibliography. Chapter 7. Acquisition and tracking of GNSS signals. 7.1 Transmission part. 7.2 Receiver architectures. 7.3 Measurement techniques. 7.4 Exercises. Bibliography. Chapter 8. Techniques for calculating positions. 8.1 Calculating the PVT solution. 8.2 Satellite's position computations. 8.3 Quantified estimation of errors. 8.4 Impact of pseudo range errors on the computed positioning. 8.5 Impact of geometrical distribution of satellites and receiver (notion of DOP). 8.6 Benefits of augmentation systems. 8.7 Discussion on interoperability and integrity. 8.8 Effect of multipath on the navigation solution. 8.9 Exercises. Bibliography. Chapter 9. Indoor positioning problem and main techniques (Non-GNSS). 9.1 General introduction to indoor positioning. 9.2 A brief review of possible techniques. 9.3 Network of sensors. 9.4 Local area telecommunication systems. 9.5 Wide-area telecommunication systems. 9.6 Inertial systems. 9.7 Recap tables and global comparisons. 9.8 Exercises. Bibliography. Chapter 10. GNSS-based indoor positioning and a summary of indoor techniques. 10.1 HS-GNSS. 10.2 A-GNSS. 10.3 Hybridization. 10.4 Pseudolites. 10.5 Repeaters. 10.6 Recap tables and comparisons. 10.7 Possible evolutions with availability of the future signals. 10.8 Exercises. Bibliography. Chapter 11. Applications of modern geographical positioning systems. 11.1 Introduction. 11.2 A chronological review of the past evolution of applications. 11.3 Individual applications. 11.4 Scientific applications. 11.5 Applications for public regulatory forces. 11.6 Systems under development. 11.7 Classifications of applications. 11.8 Privacy issues. 11.9 Current receivers and systems. 11.10 Conclusion and discussion. 11.11 Exercises. Bibliography. Chapter 12. The forthcoming revolution. 12.1 Time and space. 12.2 Development of current applications. 12.3 The possible revolution of everybody's daily life. 12.4 Possible technical positioning approaches and methods for the future. 12.5 Conclusion. 12.6 Exercises. Bibliography. Index.

Fractional Lambda Switching for Flexible Bandwidth Provisioning in WDM Networks: Principles and Performance?

A new approach is introduced in this paper to make possible a flexible utilization of WDM networks using current technology. It is shown that the bandwidth made available end-to-end by a single wavelength can be simply broken up into smaller pieces, or fraction of lambda, by relying on a worldwide common time reference system, such as GPS, previously deployed for different applications. The common time reference system is used to synchronize switches and to facilitate pipeline forwarding of data units. Pipeline forwarding is a known optimal method widely used in manufacturing and computing. It is shown how this new approach, called Time Driven Switching, behaves in terms of call blocking when the basic parameters of the scheme are varied.

Distance measurement error associated with antenna phase-center displacement in time-reference radio-positioning systems

Distance measurement error associated with antenna phase-center displacement in time-reference radio-positioning systems

A core stateless bandwidth broker architecture for scalable support of guaranteed services

We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed recently. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the per-hop behaviors of core routers and the end-to-end properties of their concatenation. We focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both per-flow end-to-end guaranteed delay services and class-based guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on a per domain basis instead of on a hop-by-hop basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of dynamic flow aggregation in providing guaranteed delay services and devise a new apparatus to effectively circumvent this problem. We conduct detailed analyses to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.

Analyses and solutions of errors on GPS/GLONASS positioning

This paper focuses mainly on the major errors and their reduction approaches pertaining to combined GPS/GLONASS positioning. To determine the difference in the time reference systems, different receiver clock offsets are introduced with respect to GPS and GLONASS system time. A more desirable method for introducing a independent unknown parameter of fifth receiver, which can be canceled out when forming difference measurements, is dicussed. The error of orbit integration and the error of transformation parameters are addressed in detail. Results of numerical integration are given. To deal with the influence of ionospheric delay, a method for forming dual-frequency ionospheric free carrier phase measurements is detailed.

Virtual time reference system: a unifying scheduling framework for scalable support of guaranteed services

We propose and develop a novel virtual time reference system as a unifying scheduling framework to provide scalable support for guaranteed services. This virtual time reference system is designed as a conceptual framework upon which guaranteed services can be implemented in a scalable manner using the DiffServ paradigm. The key construct in the proposed virtual time reference system is the notion of packet virtual time stamps, whose computation is core stateless, i.e., no per-flow states are required for its computation. We lay the theoretical foundation for the definition and construction of packet virtual time stamps. We describe how per-hop behavior of a core router (or rather its scheduling mechanism) can be characterized via packet virtual time stamps, and based on this characterization establish end-to-end per-flow delay bounds. Consequently, we demonstrate that, in terms of its ability to support guaranteed services, the proposed virtual time reference system has the same expressive power and generality as the IntServ model. Furthermore, we show that the notion of packet virtual time stamps leads to the design of new core stateless scheduling algorithms, especially work-conserving ones. In addition, our framework does not exclude the use of existing scheduling algorithms such as stateful fair queuing algorithms to support guaranteed services.

Decoupling QoS control from core routers

For scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate . Instead, QoS reservation states are stored at and managed by bandwidth broker(s). There are several advantages of such a bandwidth broker architecture. Among others, it relieves core routers of QoS control functions such as admission control and QoS state management, and thus enables a network service provider to introduce new (guaranteed) services without necessarily requiring software/hardware upgrades at core routers. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed in [20].