Explotación de nuevas oportunidades científicas de los sistemas de posicionamiento global por satélite (GNSS) desde una perspectiva intensiva en datos

[EN] With the current GNSS infrastructure development plans, over 120 GNSS satellites (including European Galileo satellites)will provide, already this decade, continuous data, in several frequencies, without interruption and on a permanent basis.This global and permanent GNSS infrastructure constitutes a major opportunity for GNSS science applications. In themeantime, recent advances in technology have contributed "de-facto" to the deployment of a large GNSS receiver arraybased on Internet of Things (IoT), affordable smart devices easy to find in everybody’s pockets. These devices – evolvingfast at each new generation – feature an increasing number of capabilities and sensors able to collect a variety ofmeasurements, improving GNSS performance. Among these capabilities, Galileo dual band smartphones receivers andAndroid’s support for raw GNSS data recording represent major steps forward for Positioning, Navigation and Timing (PNT)data processing improvements. Information gathering from these devices, commonly referred as crowdsourcing, opensthe door to new data-intensive analysis techniques in many science domains. At this point, collaboration between variousresearch groups is essential to harness the potential hidden behind the large volumes of data generated by thiscyberinfrastructure. Cloud Computing technologies extend traditional computational boundaries, enabling execution ofprocessing components close to the data. This paradigm shift offers seamless execution of interactive algorithms andanalytics, skipping lengthy downloads and setups. The resulting scenario, defined by a GNSS Big Data repository with colocatedprocessing capabilities, sets an excellent basis for the application of Artificial Intelligence / Machine Learning (ML)technologies in the context of GNSS. This unique opportunity for science has been recognized by the European SpaceAgency (ESA) with the creation of the Navigation Scientific Office, which leverages on GNSS infrastructure to deliverinnovative solutions across multiple scientific domains.[ES] Con los planes actuales de desarrollo de la infraestructura GNSS, más de 120 satélites GNSS (incluidos los satélites europeos Galileo) proporcionarán, ya en esta década, datos continuos, en varias frecuencias, sin interrupciones y de forma permanente. Esta infraestructura GNSS global y permanente constituye una gran oportunidad para las aplicaciones científicas de GNSS. Mientras tanto, avances recientes han contribuido al despliegue de una red GNSS paralela basada en la Internet de las Cosas (IoT), asequibles dispositivos inteligentes fáciles de encontrar en todos los bolsillos. Estos dispositivos, que evolucionan rápidamente con cada nueva generación, acumulan un número creciente de funcionalidades y sensores capaces de recopilar una gran variedad de mediciones. Entre estas funcionalidades, los receptores de teléfonos inteligentes de banda dual Galileo y el soporte Android para la grabación de datos GNSS sin procesar representan pasos especialmente relevantes. La recopilación de información mediante estos dispositivos, comúnmente conocida como crowdsourcing, abre la puerta a nuevas técnicas de análisis de datos en múltiples dominios científicos. Llegados a este punto, la colaboración entre diversos grupos de investigación resulta esencial para aprovechar el potencial que se esconde en los grandes volúmenes de datos generados por esta ciberinfraestructura. Las tecnologías de Cloud Computing extienden los límites computacionales tradicionales permitiendo la ejecución de componentes de procesamiento cerca de los datos. Este cambio de paradigma ofrece una rápida ejecución de algoritmos y análisis interactivos, omitiendo largas descargas y configuraciones. El escenario resultante, definido por un repositorio GNSS Big Data con capacidades de procesamiento acopladas, establece una base excelente para la aplicación de tecnologías de Inteligencia Artificial / Aprendizaje Automático (ML). Esta oportunidad única para la ciencia ha sido reconocida por la Agencia Espacial Europea (ESA) con la creación de la Oficina Científica de Navegación, que aprovecha la infraestructura GNSS para ofrecer soluciones innovadoras en múltiples dominios científicos.This work was supported by the European Space Agency as part of Research and Development Programmes under Science and Navigation Directorates. The authors would like to thank the GNSS Science Advisory Committee and ESA Navigation Support Office for their support and suggestions. We also thank our Industrial partners, involved in science use cases assessment and implementation. Thanks also to the Science and Operations technical IT Unit at ESAC supporting the deployment of the GSSC Thematic Exploitation Platform. We would like to thank all data collection providers, with special thanks to IGS, ILRS, CDDIS, BKG and IGN for their sustained and remarkable support making possible the creation of the GSSC Repository at the core of this work.Navarro, V.; Ventura-Traveset, J. (2021). A data-intensive approach to exploit new GNSS science opportunities. En Proceedings 3rd Congress in Geomatics Engineering. Editorial Universitat Politècnica de València. 43-53. https://doi.org/10.4995/CiGeo2021.2021.12740OCS435

Gravitomagnetic Clock Effect: Using GALILEO to explore General Relativity

All experiments to date are in remarkable agreement with the predictions of Einstein's theory of gravity, General Relativity. Besides the classical tests, involving light deflection, orbit precession, signal delay, and the gravitational redshift, modern technology has pushed the limits even further. Gravitational waves have been observed multiple times as have been black holes, arguably amongst the most fascinating objects populating our universe. Moreover, geodetic satellite missions have enabled the verification of yet another prediction: gravitomagnetism. This phenomenon arises due to the rotation of a central body, e.g., the Earth, which is dragging spacetime along. One resulting effect on satellite orbits is the observed Lense-Thirring effect. Another predicted, yet unverified, effect is the so-called gravitomagnetic clock effect, which was first described by Cohen and Mashhoon as the proper time difference of two counter-revolving clocks in an orbit around a rotating mass. A theoretical framework is introduced that describes a gravitomagnetic clock effect based on a stationary spacetime model. An incremental definition of a suitable observable follows, which can be accessed via orbit data obtained from the European satellite navigation system Galileo, and an implementation of the framework for use with real satellite and clock data is presented. The technical requirements on a satellite mission are studied to measure the gravitomagnetic clock effect at the state-of-the-art in satellite laser ranging and modelling of gravitational and non-gravitational perturbations. Based on the analysis within this work, a measurement of the gravitomagnetic clock effect is highly demanding, but might just be within reach in the very near future based on current and upcoming technology.Comment: 13 pages, 3 figures, 3 supplemental page

A multi-frequency method to improve the long-term estimation of GNSS clock corrections and phase biases

The space segment of the Global Navigation Satellite System (GNSS) is equipped with highly stable atomic clocks. In order to use these clocks as references, their time offsets must be estimated from ground measurements as accurately as possible. This work presents a multi-frequency and multi-constellation method for estimating satellite and receiver clock corrections, starting from unambiguous, uncombined, and undifferenced carrier-phase measurements. A byproduct of the estimation process is phase biases (i.e., the hardware delays of the carrier-phase measurements occurring at receivers and satellites). The stability and predictability of our clock estimates for receivers and satellites (GPS and Galileo) are compared with those obtained by the International GNSS Service (IGS), whereas the phase biases are assessed against two independent determinations involving combinations of carrier-phase measurements. We conclude that the method reduces day boundary discontinuities in the clock corrections, and that the estimated phase biases reproduce variabilities already observed by other authors.The present work was supported in part by the Euro-pean Space Agency contract (REL-GAL) N.4000122402/17/NL/IB, by the project RTI2018-094295-B-I00 funded bytheMCIN/AEI10.13039/501100011033whichisco-foundedby the FEDER programme, and by the Horizon 2020 MarieSkłodowska-Curie Individual Global Fellowship 797461NAVSCIN. The authors acknowledge the use of data andproducts provided by the International GNSS ServicePeer ReviewedPostprint (published version

GNSS Solar Astronomy in real-time during more than one solar cycle

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth’s ionosphere’s free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources

GENESIS: Co-location of Geodetic Techniques in Space

Improving and homogenizing time and space reference systems on Earth and, more directly, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1mm and a long-term stability of 0.1mm/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, 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 for predicting natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities which has enunciated geodesy requirements for Earth sciences. 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, proposed as 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 white paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology.Comment: 31 pages, 9 figures, submitted to Earth, Planets and Space (EPS

A Multi-User Approach to Narrowband Cellular Communications

We compare three receivers for coded narrowband transmission over a channel with fading, shadowing, and co-channel interference. The baseline receiver includes conventional diversity reception with maximal-ratio combining. A multi-user approach allows us to derive a maximum-likelihood (ML) multi-user diversity receiver and its reduced-complexity suboptimal version. Finally, a decorrelating diversity receiver, which seeks a trade-off between performance and complexity, is also studied. We consider a channel model including diversity, fading, shadowing, and interference. This can be applied, for example, to a macro-cellular wireless system with space (antenna), time, or frequency diversity. Since the shadowing process is assumed to vary slowly with respect to the transmission duration, the bit error rate should be treated as a random variable depending on the useful and interfering signal energies, which in turn depend on the shadowing process realization. This leads us to a definition o..

Co-channel interference in cellular mobile radio systems with coded PSK and diversity

In this paper, the performance of coding and diversity in narrowband wireless cellular systems affected by fading, shadowing and co-channel interference is analyzed. We consider low-order diversity, that can be practically realized for both coherent and differential phase shift keying. We assume that the shadowing random processes affecting all transmitted signals do not vary appreciably over the transmission duration. Fading, on the contrary, is assumed to vary more rapidly. Our main focus here is on outage probability. After choosing a performance indicator, its expectation is taken with respect to fading and co-channel interference, conditionally on shadowing. Hence, the resulting average performance indicator is a random variable. The probability that this random variable exceeds a specified threshold defines the outage probability. We consider as performance indicators i) the channel cut-off rate R 0 and ii) the bit error rate P b of an actual coded scheme. As we are interested in..

Enhanced GNSS-based Positioning in space exploiting Inter-Spacecraft Cooperation

The momentum taken by the space sector in the exploration of our Moon pushes private and governmental actors to intensify their efforts for launching missions to our natural satellite. In this context, novel infrastructures and techniques are being studied and experimented to reach an increased autonomy of the positioning and navigation services in the cislunar volume. Research performed in the past years have proved that Global Navigation Satellite System (GNSS) Space Service Volume could be further extended to the cislunar volume. Furthermore, both the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) have revealed their plans to design a lunar satellite system for both navigation and communications purposes. With that said, the present research revisits the concept of GNSS-Cooperative Positioning (GNSS-CP) already proven successful in the frame of terrestrial applications for space missions. The implementation of the GNSS-CP solution for space would leverage on the presence of GNSS receivers and communication links to improve the performance of the spacecraft navigation solution while implementing a non-invasive solution, hence reducing the Size, Weight and Power of the navigation sub-system. In order to demonstrate the potential benefits of GNSS-CP in space, we consider in this paper the following case scenario: The Lunar Pathfinder and Volatile and Mineralogy Mapping Orbiter (VMMO) mission. This work simulates the fusion of their respective GNSS pseudorange measurements to compute the Inter-Spacecraft Range (ISR). The reception of Galileo E5a, GPS L5, and S-Band signals are simulated. S-band signals are generated by one lunar satellite as planned by the ESA Moonlight initiative for the Lunar Communication and Navigation System (LCNS) vision. This preliminary analysis proves to be promising as a naive Least Mean Squares (LMS) estimator used on Weighted Double Differences between pseudorange observables results in an estimated distance between Pathfinder and VMMO usable to further improve the position solution of those missions