Multi-constellation GNSS orbit combination based on MGEX products

Abstract. The mission of the International GNSS Service (IGS) is to deliver highly accurate GNSS data and products to the scientific users and the community. Among these products, precise orbits, and clocks for GPS and GLONASS are available to the public. These products are system-wise combinations based on solutions provided by the Analysis Centers (AC). Over the past years, the IGS has been putting efforts in extending the service to other navigation satellite systems within the Multi-GNSS Experiment and Pilot Project (MGEX). Several ACs contribute by providing solutions containing not only GPS and GLONASS but also Galileo, BeiDou, and QZSS. However, there is no official MGEX combination so far. Therefore, we started to develop a new combination algorithm aiming at a fully consistent multi-constellation solution. We apply two different strategies focusing on the alignment of the orbits to the International Terrestrial Reference Frame (ITRF). In the first strategy, we use the Earth Rotation Parameters (ERP) to align the orbits, whereas in the second strategy Helmert parameters provided by the Terrestrial Frame Combination Center (TFCC) are applied. Based on the alignment we compare the GPS orbit products from both strategies with the official IGS orbits. These preliminary results show that the ERP strategy agrees with the official orbits around by 30 mm whereas, with the second strategy, the agreement is around 15 mm.

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Towards FAIR GNSS data: challenges and open problems

10.5194/egusphere-egu2020-18398 ◽

2020 ◽

Author(s):

Anna Miglio ◽

Carine Bruyninx ◽

Andras Fabian ◽

Juliette Legrand ◽

Eric Pottiaux ◽

...

Keyword(s):

Research Policy ◽

Global Navigation Satellite Systems ◽

International Gnss Service ◽

Open Problems ◽

Data Repositories ◽

Satellite Systems ◽

Data Practices ◽

Metadata Standards ◽

Global Navigation Satellite ◽

Gnss Data

Nowadays, we measure positions on Earth&#8217;s surface thanks to Global Navigation Satellite Systems (GNSS) e.g. GPS, GLONASS, and Galileo. Activities such as navigation, mapping, and surveying rely on permanent GNSS tracking stations located all over the world. The Royal Observatory of Belgium (ROB) maintains and operates a repository containing data from hundreds of GNSS stations belonging to the European GNSS networks (e.g. EUREF, Bruyninx et al., 2019).&#160;ROB&#8217;s repository contains GNSS data that are openly available and rigorously curated. The curation data include detailed GNSS station descriptions (e.g. location, pictures, and data author) as well as quality indicators of the GNSS observations.However, funders and research policy makers are progressively asking for data to be made Findable, Accessible, Interoperable, and Reusable (FAIR) and therefore to increase data transparency, discoverability, interoperability, and accessibility.In particular, within the GNSS community, there is no shared agreement yet on the need for making data FAIR. Therefore, turning GNSS data FAIR presents many challenges and, although FAIR data has been included in EUREF&#8217;s strategic plan, no practical roadmap has been implemented so far. We will illustrate the specific difficulties and the need for an open discussion including also other communities working on FAIR data.For example, making GNSS data easily findable and accessible would require to attribute persistent identifiers to the data. It is worth noting that the International GNSS Service (IGS) is only now beginning to consider the attribution of DOIs (Digital Object Identifiers) to GNSS data, mainly to allow data citation and acknowledgement of data providers. Some individual GNSS data repositories are using DOIs (such as UNAVCO, USA).&#160; Are DOIs the only available option or are there more suitable types of URIs (Uniform Resource Identifiers) to consider?The GNSS community would greatly benefit from FAIR data practices, as at present, (almost) no licenses have been attributed to GNSS data, data duplication is still an issue, historical provenance information is not available because of data manipulations in data centres, citation of the data providers is far from the rule, etc.To move further along the path towards FAIR GNSS data, one would need to implement standardised metadata models to ensure data interoperability, but, as several metadata standards are already in use in various scientific disciplines, which one to choose?Then, to facilitate the reuse (and long-term preservation) of GNSS data, all metadata should be properly linked to the corresponding data and additional metadata, such as provenance and license information. The latter is a good example up for discussion: despite the fact that &#8216;CC BY&#8217; license is already assigned to some of the GNSS data, other licenses might need to be enabled.&#160;Bruyninx C., Legrand J., Fabian A., Pottiaux E. (2019) &#8220;GNSS Metadata and Data Validation in the EUREF Permanent Network&#8221;. GPS Sol., 23(4), https://doi: 10.1007/s10291-019-0880-9&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;

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Analysis on the Solution of Earth Rotation Parameters with GNSS Data of CMONOC and IGS

Geomatics Science and Technology ◽

10.12677/gst.2019.71007 ◽

2019 ◽

Vol 07 (01) ◽

pp. 36-43

Author(s):

雪川李

Keyword(s):

Earth Rotation ◽

Earth Rotation Parameters ◽

Rotation Parameters ◽

Gnss Data

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An experimental combination of IGS repro3 campaign’s orbit products using a variance component estimation strategy

10.31223/x5q04f ◽

2021 ◽

Author(s):

Pierre Sakic ◽

Gustavo Mansur ◽

Benjamin Männel ◽

Andreas Brack ◽

Harald Schuh

Keyword(s):

Variance Component ◽

External Validation ◽

Terrestrial Reference Frame ◽

Variance Component Estimation ◽

International Gnss Service ◽

Combination Strategy ◽

Full Data ◽

Station Coordinates ◽

Earth Rotation Parameters ◽

Component Estimation

Over the past years, the International GNSS Service (IGS) has put efforts into reprocessing campaigns reanalyzing the full data collected by the IGS network since 1994. The goal is to provide a consistent set of orbits, station coordinates, and earth rotation parameters using state-of-the-art models. Different from the previous campaigns - namely: repro1 and repro2 - the repro3 includes not only GPS and GLONASS but also the Galileo constellation. The main repro3 objective is the contribution to the next realization of the International Terrestrial Reference Frame (ITRF2020). To achieve this goal, several Analysis Centers (AC) submitted their specific products, which are combined to provide the final solutions for each product type. In this contribution, we focus on the combination of the orbit products.We will present a consistent orbit solution based on a newly developed combination strategy where the weights are determined by a Least-Squares Variance Component Estimation (LSVCE). The orbits are combined in an iterative processing, first aligning all the products via a Helmert transformation, second defining which satellites will be used in the LSVCE, and finally normalizing the inverse of the variances as weights that are used to compute a weighted mean. Moreover, we will discuss the weight factors and their stability in the time evolution for each AC depending on the constellations. In addition, an external validation using a Satellite Laser Ranging (SLR) procedure will be shown for the combined solution.

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Combination of GNSS and VLBI data for consistent estimation of Earth Rotation Parameters

10.5194/egusphere-egu21-10768 ◽

2021 ◽

Author(s):

Lisa Lengert ◽

Claudia Flohrer ◽

Anastasiia Girdiuk ◽

Hendrik Hellmers ◽

Daniela Thaller

Keyword(s):

Time Series ◽

Earth Rotation ◽

Polar Motion ◽

Normal Equation ◽

Station Coordinates ◽

Earth Rotation Parameters ◽

Vlbi Data ◽

Rotation Parameters ◽

Gnss Data ◽

The Impact

We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.&#160; The main goal of the combined analyses of the two different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, i.e., mainly Earth Rotation Parameters (ERPs), but also station coordinates and tropospheric parameters through local ties and atmospheric ties, respectively.Based on our previous combination studies using GNSS data and VLBI Intensive sessions on a daily and multi-day level, we generate a consistent, low-latency ERP time series with a regular daily resolution for polar motion and dUT1. We achieved in this way a significant accuracy improvement of the dUT1 time series and a slight improvement of the pole coordinates time series, comparing ERPs from the combined processing with the individual technique-specific ERPs.In our recent studies, we extend the combination of GNSS and VLBI Intensive sessions by adding VLBI 24-hour sessions in order to exploit the benefit of the combination to its maximum extend. We analyse the impact of the combination on the global parameters of interest, i.e., mainly dUT1, polar motion and LOD, but also on station coordinates.BKG&#8217;s primary interest is the combination of GNSS and VLBI data on the observation level. However, the current combination efforts are based on the normal equation level using technique-specific SINEX files as a starting point.

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Assessment of geodetic products from Multi-GNSS analyses at the Onsala site

10.5194/egusphere-egu21-14343 ◽

2021 ◽

Author(s):

Periklis-Konstantinos Diamantidis ◽

Grzegorz Kłopotek ◽

Rüdiger Haas ◽

Jan Johansson

Keyword(s):

Global Navigation Satellite Systems ◽

Observation Data ◽

International Gnss Service ◽

Satellite Systems ◽

Triple Frequency ◽

Software Packages ◽

Combined Solution ◽

Gnss Receivers ◽

Global Navigation Satellite ◽

Gnss Data

The dawn of Beidou and Galileo as operational Global Navigation Satellite Systems (GNSS) alongside Global Positioning System (GPS) and GLONASS as well as new features that are now present in all GNSS, such as a triple-frequency setup, create new possibilities concerning improved estimation and assessment of various geodetic products. In particular, the multi-GNSS analysis gives an access to a better sky coverage allowing for improved estimation of zenith wet delays (ZWD) and tropospheric gradients (GRD), and can be used to determine integer phase ambiguities. The Multi-GNSS Experiment (MGEX), as realised by the International GNSS Service (IGS), provides orbit, clock and observation data for all operational GNSS. To take advantage of the new capabilities that these constellations bring, space-geodetic software packages have been retrofitted with Multi-GNSS-compliant modules. Based on this, two software packages, namely GipsyX and c5++, are utilised by way of the static Precise Point Positioning (PPP) approach using six months of data, and an assessment of the derived geodetic products is carried out for several GNSS receivers located at the Onsala core site. More specifically, we perform both single-constellation and multi-GNSS data analysis using Kalman filter and least-squares methods and assess the quality of the derived station positions, ZWD and GRD. A combined solution using all GNSS constellations is carried out and the improvement with respect to station position repeatabilities is assessed for each station. Results from the two software packages are compared with respect to each other and the discrepancies are discussed. Inter-system biases, which homogenise the different time scale that each GNSS operates in, and are necessary for the multi-GNSS combination, are estimated and presented. Finally, the applied inter-system weighting and its impact on the derived geodetic products are discussed.

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Assessment of geodetic products from MGEX analyses for the Onsala site

10.5194/egusphere-egu2020-965 ◽

2020 ◽

Author(s):

Periklis-Konstantinos Diamantidis ◽

Grzegorz Klopotek ◽

Rüdiger Haas

Keyword(s):

Global Navigation Satellite Systems ◽

Observation Data ◽

International Gnss Service ◽

Satellite Systems ◽

Troposphere Gradients ◽

Combined Solution ◽

Gnss Receivers ◽

Global Navigation Satellite ◽

Gnss Data

<div>The emergence of BeiDou and Galileo as operational Global Navigation Satellite Systems (GNSS), in addition to Global Positioning System (GPS) and GLONASS which are already in use, opens up possibilities in delivering geodetic products with higher precision. Apart from ensuring the homogeneity of the derived products, multi-GNSS analysis takes the advantage of new frequencies and an improved sky coverage. This should lead to better phase ambiguity resolution and an improved estimation of target parameters such as zenith wet delays (ZWD), troposphere gradients (GRD) and station positions. The International GNSS Service (IGS) has realised this potential by initiating the Multi-GNSS Experiment (MGEX) which provides orbit, clock and observation data for all operational GNSS. Correspondingly, the multi-technique space geodetic analysis software c5++ has been augmented with a MGEX-compliant GNSS module. Based on this new module and the Precise Point Positioning (PPP) approach using six-month of data, an assessment of the derived geodetic products is carried out for several GNSS receivers located at the Onsala core site. More specifically, we perform both single- and multi-GNSS data analysis using Kalman filter and least-squares methods and assess the quality of the derived station positions, ZWD and GRD. A combined solution using all GNSS together is carried out and the improvement with respect to station position repeatabilities is assessed for each station. Inter-system biases, which homogenise the different time scale that each GNSS operates in and are necessary for the multi-GNSS combination, are estimated and presented. Finally, the applied inter-system weighting is discussed as well as its impact on the derived geodetic products.</div>

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Astrometric Latitude and Time Observational Database at Shanghai Observatory

Symposium - International Astronomical Union ◽

10.1017/s007418090017367x ◽

1993 ◽

Vol 156 ◽

pp. 433-433

Author(s):

Zheng-Xin Li ◽

You-Fen Chen ◽

Chang-Xia Qian

Keyword(s):

Observational Data ◽

Earth Rotation ◽

International Earth Rotation Service ◽

The Past ◽

International Earth Rotation ◽

Earth Rotation Parameters ◽

The World ◽

Time Determination ◽

Rotation Parameters ◽

The Moment

After the closing of Bureau International de L'Heure (BIH) and the establishment of International Earth Rotation Service (IERS) at the end of 1987. Shanghai Observatory has been the institute where the astrometric latitude and time observational data are collected and treated. During the past four years, about 75,293 measurements in latitude or time determination have been obtained by the 64 optical astrometric instruments over the world from which the five-day Earth Rotation Parameters of the 1988–1990 period have still been reduced. Twelve Quarterly Report on the optical ERP have been distributed. Since the beginning of 1991 the regular reduction of the ERP has been stopped but the collecting of the observational data is still going on in Shanghai Observatory in order to meet the requirements of the scientists who are still interested on the studies concerned with these observations. There are still 42 optical astrometric instruments taking part into the regular observations at the moment.

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An experimental combination of IGS repro3 campaign’s orbit products using a variance component estimation strategy

10.31223/x5k614 ◽

2021 ◽

Author(s):

Pierre Sakic ◽

Gustavo Mansur ◽

Benjamin Männel ◽

Andreas Brack ◽

Harald Schuh

Keyword(s):

Variance Component ◽

External Validation ◽

Terrestrial Reference Frame ◽

Variance Component Estimation ◽

International Gnss Service ◽

Combination Strategy ◽

Full Data ◽

Station Coordinates ◽

Earth Rotation Parameters ◽

Component Estimation

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Precise Galileo orbit determination using combined GNSS and SLR observations

10.5194/egusphere-egu2020-340 ◽

2020 ◽

Author(s):

Grzegorz Bury ◽

Krzysztof Sośnica ◽

Radosław Zajdel ◽

Dariusz Strugarek

Keyword(s):

Orbit Determination ◽

Reference Frames ◽

European Space Agency ◽

Pilot Project ◽

Laser Ranging ◽

Navigation Satellite ◽

International Gnss Service ◽

Terrestrial Reference Frames ◽

Gnss Data ◽

The Impact

The European navigation system Galileo is on its final stretch to become a fully operational capability (FOC) Global Navigation Satellite System (GNSS). The current constellation consists of 24 healthy satellites decomposed into three Medium Earth Orbits and since late 2016 is considered as an operational system. So far, the official Galileo orbits are provided by the European Space Agency and in the frame of the International GNSS Service (IGS) Multi-GNSS pilot project (MGEX) whose one of the goals is to develop orbit determination strategies for all new emerging navigation satellite systems.All the Galileo satellites are equipped with Laser Retroreflector Arrays (LRA) for Satellite Laser Ranging (SLR). As a result, a number of Galileo satellites is tracked by laser stations of the International Laser Ranging Service (ILRS). SLR measurements to GNSS, such as Galileo, comprise a valuable tool for the validation of the orbit products as well as for an independent orbit solution based solely on laser ranging data. However, the SLR data may be used together along with the GNSS observations for the determination of the combined GNSS orbit using the two independent space techniques co-located onboard the Galileo satellites. The Galileo orbit determination strategies, as well as the usage of laser ranging to the navigation satellites, is crucial, especially in the light of the discussion concerning possible usability of the Galileo observation in the future realizations of the International Terrestrial Reference Frames.&#160;&#160; &#160;In this study, we present results from the precise Galileo orbit determination using the combined GNSS data transmitted by the Galileo satellites and the range measurements performed by the ILRS stations. We test different weighting strategies for GNSS and SLR observations. We test the formal errors of the Keplerian elements which significantly decrease when we apply the same weights for SLR &#160;and GNSS data. However, in such a manner, we deteriorate the internal consistency of the solution, i.e., the orbit misclosures. &#160;For the solution with optimal weighting strategy, we present results of the quality of Galileo orbit predictions based on the combined solutions, as well as the SLR residuals. The combined GNSS+SLR solution seems to be especially favorable for the Galileo In-Orbit Validation (IOV) satellites, for which the standard deviation (STD) of the SLR residuals decreases by 13% as compared to the microwave solutions, whereas for the Galileo-FOC satellite the improvement of the STD of SLR residuals is at the level of 9%. Finally, we test the impact of adding SLR observations to the LAGEOS satellites which stabilizes the GNSS solutions, especially in terms of the realization of terrestrial reference frame origin.&#160;

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Twenty-Five Years of the International GNSS Service

10.5194/egusphere-egu2020-6153 ◽

2020 ◽

Author(s):

Allison Craddock ◽

Gary Johnston ◽

Felix Perosanz ◽

Rolf Dach ◽

Charles Meertens ◽

...

Keyword(s):

Reference Frame ◽

Open Data ◽

Cost Effective ◽

Satellite System ◽

Terrestrial Reference Frame ◽

International Gnss Service ◽

Quarter Century ◽

Long Baseline ◽

International Terrestrial Reference Frame ◽

Gnss Data

For over twenty-five years, the International Global Navigation Satellite System (GNSS) Service (IGS) has carried out its mission to advocate for and provide freely and openly available high-precision GNSS data and products.The IGS is an essential component of the IAG&#8217;s Global Geodetic Observing System (GGOS), where it facilitates cost-effective geometrical linkages with and among other precise geodetic observing techniques, including: Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the International Terrestrial Reference Frame (ITRF).&#160; As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service, and at its heart is a strong culture of sharing expertise, infrastructure, and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world.This poster will present an update on current IGS products and operations, as well as highlights on recent organizational developments and community activities. The impacts and benefits of global cooperation and openly available data will be emphasized, and information about the IGS stations and network, contributions to the International Terrestrial Reference Frame solutions, and product applications will be presented. A summary of IGS products, with emphasis on analysis, coordination, applications, and their availability will be described. Information about efforts to form new groups supporting product generation within IGS open data and product policies will be included. Information about the themes and topics of discussion for the upcoming 2020 IGS Workshop in Boulder, Colorado, USA will also be provided.

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