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.
Since 1994, the International GNSS Service (IGS) provides a combination of orbit and clock offset products from its different Analysis Centers. These products are used as input by many software for countless scientific and/or operational applications. They can also be used as an independent reference for benchmark experiments. Nevertheless, those products include GPS-only data, despite the fact that nowadays several GNSS constellations are available. We performed modifications on the existing IGS combination software and made it compatible with multi-GNSS products. We present here the results of a combination of five Multi-GNSS Experiment Analysis Centers (ACs) for five constellations (GPS + GLONASS + Galileo + Beidou + QZSS) from GPS week 1800 to 2000. The RMS of combined orbit w.r.t. input ACs ones are ~ 3±1.5cm for recent weeks of the test period.
Since 1994, the International GNSS Service (IGS) provides a combination of orbit and clock offset products from its different Analysis Centers. These products are used as input by many software for countless scientific and/or operational applications. They can also be used as independent reference for benchmark experiments. Nevertheless, those products include GPS/GLONASS-only data, despite the fact that nowadays several GNSS constellations are available. We performed modifications on the existing IGS combination software and made it compatible with multi-GNSS products. We present here the results of a combination of five Multi-GNSS Experiment Analysis Centers (ACs) for five constellations (GPS + GLONASS + Galileo + Beidou + QZSS) from GPS week 1800 to 2000 (July 2014 to May 2018). The RMS of combined orbit w.r.t. input ACs ones are ∼ 30±15 mm for recent weeks of the test period.
Over the past years, the International GNSS Service (IGS) has been putting efforts into extending its service towards the Multi-GNSS Experiment and Pilot Project (MGEX). Several MGEX Analysis Centers (ACs) contribute by providing solutions containing not only GPS and GLONASS but also Galileo, BeiDou, and QZSS. The MGEX orbit and clock combination is a product that is still not consolidated inside the IGS and requires studies in order to provide a consistent solution. In this contribution, we present a least-squares framework for a multi-GNSS orbit combination, where the weights used to combine the ACs' orbits are determined by least-squares variance component estimation. We introduce and compare two weighting strategies, where either AC specific weights or AC and constellation specific weights are used. Both strategies are tested using MGEX orbit solutions for a period of two and a half years. They yield similar results with an agreement with the ACs' orbits at the one centimeter level for GPS and up to a few centimeters for the other constellations. The agreement is generally slightly better with the AC and constellation weighting. A comparison of our combination approach with the official combined IGS final solution using three years of GPS, and GLONASS orbits from the regular IGS processing shows an agreement of better than 5 mm and 12 mm for GPS and GLONASS, respectively. An external validation using Satellite Laser Ranging (SLR) is performed for our combined MGEX orbit solutions with both weighting schemes.
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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