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[EN] The monitoring of bridges is a crucial operation for their maintenance and safe operation. Several methodologies have been developed the last decades, where different sensors are deployed to measure the bridge response (displacement, acceleration, tilt, strain, etc.). GNSS technology is one of the methods which are applied with the main advantage the direct measurement of the bridge displacement is carried out in an independent global coordinate system. However, the high cost of the GNSS stations, consisted of dual frequency receiver and geodetic GNSS antenna, is the main reason of the limited application of GNSS for bridge monitoring. In the current study, we assess the accuracy of low-cost multi-GNSS receivers in monitoring dynamic motion, similar to that of bridge response. The precision of low-cost GNSS receivers was assessed against high-performance dual frequency GNSS receivers, by executing controlled circular motion of predefined radius, of amplitude ranging between 5 to 50 cm, and frequency of 0.363 Hz. From the analysis of the GNSS measurements it was assessed the precision of GPS-only and the potential beneficial contribution of multi-GNSS constellation by enhancing the accuracy of GNSS solution. Then, a low-cost monitoring system formed by two closely-spaced low-cost GNSS receivers was applied in dynamic displacement monitoring of the Wilford pedestrian bridge. The analysis from low-cost GNSS data shows similar accuracy in monitoring the bridge dynamic response to that of the survey-grade GNSS receiver, with same main modal frequency of the bridge identified.

As one of the most important parameters, water vapor is very valuable for the studies of extreme weather events and climatic phenomena. The GNSS have been proven to be a relatively new technique for sounding atmospheric water vapor which has experienced unprecedented developments over the past decade due to the rapid deployment of wide-spread space- and ground-based infrastructures. This significant development and the long-term accumulation of GNSS data, has offered a strong data support and new opportunity to advance our understanding of climate change and extreme weather events. In the meanwhile, the fifth resurgence of artificial intelligence (AI) technology has empowered us in the ability of big geodetic data analytics and data mining. All these have helped us in the understanding the atmospheric dynamic process, and mining the detailed information of the formation, evolution, development and dissolution of extreme weather events and complicated atmospheric process.This contribution presents a summary of our 10-year relevant research in the area that involves a full spatial domain of ground-, air- and space-based systems and a comprehensive technological domain of GNSS/geodesy, remote sensing, meteorology and atmosphere. First, the background, current status and recent international frontier developments of the GNSS tropospheric sounding technique are summarized. Then, the theory, technical features and major advancement of the GNSS-derived atmospheric products in the applications of climate analyses and extreme weather forecasting are presented. Finally, the challenges, opportunities and future prospectives in terms of the technique and its innovative applications of national and international significance are provided., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The GNSS multipath delay error is highly related to the surrounding monitoring environment, which cannot be eliminated or mitigated by establishing the double difference observation model. In the actual monitoring environment, due to the complexity of the multi-GNSS constellation, it is difficult for existing algorithms to consider GEO, IGSO, MEO and other different orbital types of satellites for real-time and efficient multipath error reduction. Therefore, this paper proposes a novel GNSS dual-frequency multipath error reduction method for real deformation monitoring for GNSS considering various satellite orbit types. This method extracts the single error residual of each satellite based on the assumption of "zero mean", and divides the appropriate grid density of GEO and IGSO\MEO respectively, to construct the dual-frequency multi-path hemispherical map model suitable forGNSS satellites with different orbital types. This method can realize the multi-path error elimination of the observed values of different orbits and different frequencies. The results of simulation experiments and real deformation monitoring data demonstrate that this method can effectively eliminate low-frequency multipath delay errors in the observation domain and coordinate domain. After multipath correction, the precision of the horizontal coordinates and height coordinates is 1.7mm and 4.6mm. The precision of the horizontal coordinate and height coordinate is increased by 50% and 60% respectively. The fixed rate of ambiguity increased by 5%~7%., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)