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36. Real-time GNSS Service at GFZ: Current Status and Recent Development

Author

Wang, Jungang, Jiang, Xinyuan, Tang, Longjiang, Qin, Zhiwei, Zuo, Xiang, Cui, Bobin, Ge, Maorong, and Schuh, Harald

Abstract

Real-time Global Navigation Satellite Systems (GNSS) are critical for precise and reliable positioning, navigation, and timing (PNT) services, including both civil applications with an accuracy of meter-level and geohazard early warning systems with an accuracy of cm- or even mm-level. For high-precision real-time GNSS applications, the precise orbits, clocks, hardware delays, and atmospheric information are estimated and disseminated in real time by the service provider. In this study, we introduce the current status and recent developments of the GFZ GNSS real-time analysis center. We introduce the data processing strategy for generating satellite orbits and clocks, hardware delays, and atmospheric information, and present the accuracy of the online operational products. We focus on the recent developments in improving the accuracy and reducing the latency of real-time products, such as shortening the ultra-rapid orbit processing time and improving the predicting accuracy, estimating orbits with real-time streaming data, and adopting the un-differenced ambiguity resolution in the estimation of real-time clocks and orbits. Lastly, we evaluate the real-time positioning performance using the GFZ real-time products, and demonstrate with the atmospheric augmentation information, the cm-level accuracy can be achieved within a few minutes., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

37. Applying tropospheric ties in GNSS and vlbi integrated solution: Impact of deterministic and stochastic uncertainty

Author

Wang, Jungang, Glaser, Susanne, Balidakis, Kyriakos, Ge, Maorong, Heinkelmann, Robert, and Schuh, Harald

Abstract

For microwave-based space geodetic techniques, co-located instruments within a few hundred meters are considered to share the same troposphere, and thus intra-/inter-technique tropospheric ties can be applied to improve the multi-technique integrated solution. The concept of applying tropospheric ties assumes that tropospheric parameters from each technique represent the true tropospheric state, i.e., (1) there should be no technique-related systematic bias, and (2) the technique-specific stochastic noise that leaks into atmospheric delay estimates should be minimized. However, this is usually not the case in reality, as the modeling and parameter estimation in the analysis of space geodetic techniques naturally contain systematic and stochastic uncertainty. For example, the multi-path effect and antenna phase center variation (PCV) error could introduce systematic biases in Global Navigation Satellite Systems (GNSS) tropospheric parameters, and the limitation of observation geometry in Very Long Baseline Interferometry (VLBI) could bias the horizontal gradients. Therefore, it is critical to identify and handle the systematic biases, and properly handle the stochastic part. In this study, we demonstrate that tropospheric parameter biases could be large, e.g., up to 5 mm in zenith total delay (ZTD). Ignoring systematic biases distorts the ground network, especially the VLBI network. For example, the systematic bias in ZTD shifts the network scale, and the bias in horizontal gradients rotates the network and deteriorates earth orientation parameters (EOP). We demonstrate that the GNSS and VLBI integrated solution can be improved after properly handling the tropospheric ties., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

40. A new large-area hierarchical PPP-RTK service strategy.

Author

Cui, Bobin, Jiang, Xinyuan, Wang, Jungang, Li, Pan, Ge, Maorong, and Schuh, Harald

Abstract

Introducing precise atmosphere information into precise point positioning enables rapid ambiguity resolution and introduces a significant accuracy improvement. However, it can only be implemented in regions with dense networks and stable communication links. For larger areas, e.g., an intercontinental level, there is a conflict between the accuracy of corrections and the amount of atmosphere information to be disseminated. We develop a hierarchical augmentation mode to combine the advantages of the fitting model and region interpolation model to relieve the communication burden. Relying on the fitting model with fewer coefficients applied over large areas as the essential information, the unmodeled errors are calculated at each reference station, and further correction information is optional compensation depending on the magnitude of the unmodeled residuals. We perform the proposed models on 103 EUREF Permanent Network stations with 200-km station spacing and 84 stations as the external validation. The ionosphere and troposphere fitting models have an average accuracy of about 4.2 and 1.3 cm, respectively, under meteorologically calm conditions. The unmodeled error transmission determined by the magnitude of residuals can be reduced by 61% and 96% for the ionospheric and tropospheric delays, respectively, with respect to the legacy interpolation mode. Further compensation implemented, i.e., unmodeled residuals, can achieve instantaneous convergence for 83.6% of all solutions, and the overall initialization time is within 1.0 min. Thus, the proposed hierarchical positioning mode satisfies real-time positioning convergence requirements and significantly reduces massive corrections in communication. [ABSTRACT FROM AUTHOR]

Published
2023
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