AATR an ionospheric activity indicator specifically based on GNSS measurements

This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.Postprint (published version

Assessing the quality of ionospheric models through GNSS positioning error: methodology and results

Single-frequency users of the global navigation satellite system (GNSS) must correct for the ionospheric delay. These corrections are available from global ionospheric models (GIMs). Therefore, the accuracy of the GIM is important because the unmodeled or incorrectly part of ionospheric delay contributes to the positioning error of GNSS-based positioning. However, the positioning error of receivers located at known coordinates can be used to infer the accuracy of GIMs in a simple manner. This is why assessment of GIMs by means of the position domain is often used as an alternative to assessments in the ionospheric delay domain. The latter method requires accurate reference ionospheric values obtained from a network solution and complex geodetic modeling. However, evaluations using the positioning error method present several difficulties, as evidenced in recent works, that can lead to inconsistent results compared to the tests using the ionospheric delay domain. We analyze the reasons why such inconsistencies occur, applying both methodologies. We have computed the position of 34 permanent stations for the entire year of 2014 within the last Solar Maximum. The positioning tests have been done using code pseudoranges and carrier-phase leveled (CCL) measurements. We identify the error sources that make it difficult to distinguish the part of the positioning error that is attributable to the ionospheric correction: the measurement noise, pseudorange multipath, evaluation metric, and outliers. Once these error sources are considered, we obtain equivalent results to those found in the ionospheric delay domain assessments. Accurate GIMs can provide single-frequency navigation positioning at the decimeter level using CCL measurements and better positions than those obtained using the dual-frequency ionospheric-free combination of pseudoranges. Finally, some recommendations are provided for further studies of ionospheric models using the position domain method.Peer ReviewedPostprint (published version

gLAB hands-on education on satellite navigation

The Global Navigation Satellite System (GNSS) allows computing the Position, Velocity and Time (PVT) of users equipped with appropriate hardware (i.e. an antenna and a receiver) and software. The latter estimates the PVT from the ranging measurements and ephemeris transmitted by the GNSS satellites in frequencies of the L band. The research group of Astronomy and Geomatics (gAGE) at the Universitat Politecnica de Catalunya (UPC) has been developing the GNSS LABoratory (gLAB) tool suite since 2009, in the context of the European Space Agency (ESA) educational program on satellite navigation (EDUNAV). gLAB is a multi-purpose software capable of determining the PVT in several modes: stand-alone (e.g. as a smartphone or car navigator), differential (e.g. surveying equipment or precise farming), and augmented with integrity (e.g. civil aviation or safety of life applications). gLAB has been designed for two main sets of users and functions. The first one is to educate University students and professionals in the art and science of GNSS data processing. This includes newcomers to the GNSS field that highly appreciate the Graphical User Interface (GUI), the default templates with the necessary configuration or the messages with warnings and errors. The second group of users are those with previous experience on GNSS. Those are interested into a high computation speed, high-accuracy positioning, batch processing and access to the intermediate computation steps. In the present contribution, we present some examples in which gLAB serves as an education platform. The data sets are actual GNSS measurements collected by the publicly available International GNSS Service (IGS), together with other IGS products such as the satellite orbits and clocks broadcast in the navigation message. The proposed methodology and procedures are tailored to understand the effects of different error components in both the Signal in Space (SIS) and the position domain, by activating or deactivating different modeling terms in gLAB. The results illustrate some examples of how the PVT can be enhanced or deteriorated when using different processing strategies or propagation effects present in the GNSS signals traversing the atmosphere, among others. We conclude that gLAB is a useful tool to learn GNSS data processing or to expand any prior knowledg

EGNOS 1046 maritime service assessment

The present contribution evaluates how the European Geostationary Navigation Overlay System (EGNOS) meets the International Maritime Organization (IMO) requirements established in its Resolution A.1046 for navigation in harbor entrances, harbor approaches, and coastal waters: 99.8% of signal availability, 99.8% of service availability, 99.97% of service continuity and 10 m of horizontal accuracy. The data campaign comprises two years of data, from 1 May 2016 to 30 April 2018 (i.e., 730 days), involving 108 permanent stations located within 20 km of the coast or in islands across the EGNOS coverage area, EGNOS corrections, and cleansed GPS broadcast navigation data files. We used the GNSS Laboratory Tool Suite (gLAB) to compute the reference coordinates of the stations, the EGNOS solution, as well as the EGNOS service maps. Our results show a signal availability of 99.999%, a horizontal accuracy of 0.91 m at the 95th percentile, and the regions where the IMO requirements on service availability and service continuity are met. In light of the results presented in the paper, the authors suggest the revision of the assumptions made in the EGNOS Maritime Service against those made in EGNOS for civil aviation; in particular, the use of the EGNOS Message Type 10.This research was funded by the European GNSS Agency within the framework Integration of the Fundamental Elements, Contract GSA/OP/12/16/Lot1/SC1, and the APC was funded by the Spanish Ministry of Science, Innovation and Universities Project RTI2018-094295-B-I00.Peer ReviewedPostprint (published version

Implementació de models ionosfèrics de GNSS en gLAB

gLAB is an open source tool developed in gAGE group under the terms of an ESA contract. It currently processes full GPS data, being capable of doing precise point positioning.[ANGLÈS] gLAB is an open source tool developed in gAGE group under the terms of an ESA contract. It currently processes full GPS data, being capable of doing precise point positioning. With the appearance of new satellite systems and enhanced algorithms, new ionosphere models for satellite systems have appeared. It is then necessary to make an update of gLAB in order to include this new models.[CASTELLÀ] gLAB es una herramienta de código abierto desarrollado por el grupo gAGE bajo un contrato de la ESA. Actualmente procesa todos los datos de GPS, siendo capaz de hacer posicionamiento de punto preciso. Con la aparición de nuevos sistemas de satélites y mejores algoritmos, han aparecido nuevos modelos de la ionosfera para los diferentes sistemas de satélites. Por lo tanto, es necesario realizar una actualización de gLAB con el fin de incluir estos nuevos modelos.[CATALÀ] gLAB és una eina de codi obert desenvolupat pel grup gAGE sota un contracte de la ESA. Actualment processa totes les dades de GPS, sent capaç de fer posicionament de punt precís. Amb l'aparició de nous sistemes de satèl·lits i millors algorismes, han aparegut nous models de la ionosfera pels diferents sistemes de satèl·lits. Per tant, és necessari realitzar una actualització de gLAB amb la finalitat d'incloure aquests nous models

Actualització de gLAB per a processament de dades de EGNOS

gLAB is a free open-source software to process GNSS data. The first release of this software package allows full processing capability of GPS data, and partial han- dling of Galileo and GLONASS data.gLAB is a free open-source software to process GNSS data. The first release of this software package allows full processing capability of GPS data, and partial handling of Galileo and GLONASS data. EGNOS is the european satellite augmentation system which provides integrity and accuracy to GNSS positioning. This upgrade will make gLAB one of the few free and open source applications able to process EGNOS data.gLAB es un software gratuito de código abierto para procesar datos GNSS. La primera versión de este paquete de software permite la capacidad de procesamiento completo de datos GPS y la manipulación parcial de datos de Galileo y GLONASS. EGNOS es el sistema europea de aumentación por satélite que proporciona integridad y exactitud en posicionamiento GNSS. Esta actualización hará que gLAB una de las pocas aplicaciones de código libre y abierto capaces de procesar datos de EGNOS.gLAB és un programari gratuït de codi obert per processar dades GNSS. La primera versió d'aquest programa permet la capacitat de processament complet de dades GPS i la manipulació parcial de dades de Galileo i GLONASS. EGNOS és el sistema europeu d'augmentació per satèl·lit que proporciona integritat i exactitut en posicionament GNSS. Aquesta actualització farà que gLAB sigui una de les poques aplicacions de codi lliure i obert capaços de processar dades de EGNOS

Assessment of Ionospheric Corrections Algorithms Using the GNSS Laboratory Tool Suite (gLAB): From STEC to Navigation Performance

Users of the Global Navigation Satellite System (GNSS) using a single-frequency receiver need to use an Ionospheric Correction Algorithm (ICA) to compensate the delay introduced by the Ionosphere on radio waves. The European GNSS, Galileo, uses an ICA named NeQuick-G since it is an adaptation to real time use of the 3D climatological model NeQuick, whereas the American Global Positioning Service (GPS) uses the Klobuchar ICA, which was also adopted initially by the Chinese GNSS, Beidou. In an effort to foster the adoption of NeQuick-G by final users, two implementations in C language were made publicly available by the European Space Agency (ESA) and the Joint Research Centre (JRC) of the European Commission (EC) respectively. The latter, was chosen to be integrated in the GNSS laboratory tool suite (gLAB), developed by the research group of Astronomy and Geomatics (gAGE) of the Universitat Politecnica de Catalunya (UPC) because its open license and its processing speed. The aim of the present contribution is to compare the Slant Total Electron Content (STEC) predictions of the two aforementioned ICAs and assess their differences in the navigation domain using the gLAB tool. For this purpose, we have used multi-frequency data for several hundreds of stations distributed worldwide belonging to the International GNSS Service (IGS) network. For each first day of the month during year 2019, the outcomes STECs of the two ICAs have been compared in terms of accuracy, availability and execution time. For completeness and inter-comparisons, STEC from post-processed Global Ionospheric Maps from IGS have been also been accounted for. Then, for each station involved in the experiment, positioning errors have been analyzed while using the different ionospheric corrections.The authors acknowledge the use of data and products provided by the International GNSS Service. The research reported in this paper has been partially supported by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN and by the Spanish Ministry of Science, Innovation and Universities project RTI2018-094295-B-I00 a.Peer ReviewedPostprint (published version

Galileo Ionospheric Correction Algorithm Integration into the Open-Source GNSS Laboratory Tool Suite (gLAB)

Users of the global navigation satellite system (GNSS) operating with a single-frequencyreceiver must use an ionospheric correction algorithm (ICA) to account for the delay introduced onradio waves by the upper atmosphere. Galileo, the European GNSS, uses an ICA named NeQuick-G. In an effort to foster the adoption of NeQuick-G by final users, two implementations in Clanguage have been recently made available to the public by the European Space Agency (ESA)and the Joint Research Centre (JRC) of the European Commission (EC), respectively. The aim ofthe present contribution is to compare the slant total electron content (STEC) predictions of thetwo aforementioned implementations of NeQuick-G. For this purpose, we have used actual multi-constellation and multi-frequency data for several hundreds of stations distributed worldwidebelonging to the Multi GNSS Experiment (MGEX) network of the International GNSS Service (IGS).For each first day of the month during year 2019, the STECs of the two NeQuick-G versions werecompared in terms of accuracy, consistency, availability, and execution time. Our study concludesthat both implementations of NeQuick-G perform equivalently. Indeed, in over 99.998% of the 2125million STECs computed, the output is exactly coincident. In contrast, 0.002% of the whole set ofSTECs for those rays are tangent to the Earth, the behavior of both implementations differs. Weconfirmed the discrepancy by processing radio-occultation actual measurements from a COSMIC-2 low Earth orbit satellite. We selected the JRC version of the Galileo ICA to be integrated intothe GNSS LABoratory (gLAB) tool suite, because its open license and its processing speed (it is13.88% faster than the ESA version). NeQuick-G outperforms the GPS ICA in STEC residuals up to12.15 TECUs (percentile 96.23th) and in the 3D position errors, up to 5.76 m (percentile 99.18th) forcode-pseudorange positioning.This work was supported in part by the Spanish Ministry of Science, Innovation andUniversities project RTI2018-094295-B-I00 and in part by the Horizon 2020 Marie Skłodowska-Curie Individual Global Fellowship 797461 NAVSCIN.Peer ReviewedPostprint (published version

Experiments on the Ionospheric Models in GNSS

In GNSS, one of the main error sources of the Standard Positioning Service (SPS) is introduced by the ionosphere. Although this error can be cancelled by combining two signals at different frequencies, most of the single - frequency mass - market receivers do not benefit from this cancel l ation. For that reason, a set of parameter s is included in the navigation message in order to compute the ionospheric delay of any observation by the Klobuchar model. The Klobuchar model is a very simple model that is able to remove more than the 50% of the ionospheric delay. Recently, more accurate ionospheric models have been introduced such as Global Ionospheric Map (GIM) or the F ast P recise P oint P ositioning ( F PPP ) ionospheric model. In previous works, with data gathered in Europe, it was shown the advantage of the F PPP’s ionospheric model. In this work, we conduct experiments to compare the performance of different ionospheric modelling methods including: Klobuchar, GIM s and F PPP. Our preliminary results show how F PPP and GIM s lead to better positioning precisions compared to the Klobuchar model. However, since data is not wide enough to cover different ionospheric cond itions, more experiments will be carried out in our future work to validate the current result s .Peer Reviewe