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Objectives: Facing the demand for mobile intelligent services in the era of internet of everything, it is an urgent need to establish an aerial-ground collaborative intelligent service platform. Due to the limitations of core equipments and algorithms, the development of aerial-ground collaborative mobile intelligent service platform is relatively slow. Methods: Therefore, we break through the core technologies of realtime position and attitude measurement of sensors, develop the airborne and vehicle mounted aerial-ground multi-platform collaborative networking remote sensing observation system, and realize the quality improvement and intelligent and fine processing of multi-source remote sensing images, which can effectively support remote sensing mapping services, and improve the level of automatic processing of remote sensing information. Results: Thus, our research solves the problems of “accuracy, speed and flexibility” in the aerial-ground collaborative intelligent service platform, and realizes the global autonomous positioning of “BeiDou navigation satellite system with position and attitude measuring instrument”, rapid target searching under the aerial-ground collaborative networking, and automatic change checking under intelligent processing. Conclusions: The aerial-ground collaborative mobile intelligent service platform has been widely used in the monitoring of geographical conditions, smart city planning and construction, emergency mapping support and other industries. [ABSTRACT FROM AUTHOR]

Objectives: Discovering a moving target and obtaining its geographic position and moving speed is a very important and highly accurate application for optical video satellites. Generally, existing stabilization approaches for optical video satellites can obtain stable and smooth videos. However, these stabilized satellite videos often have no geometric information, which makes them difficult to meet the application requirements. To solve this problem, a geo-coded stabilization approach for optical video satellites in object space is proposed. Methods: The proposed approach takes full advantage of the orientation parameter information of satellite video frames. Firstly, an interframe motion model based on the frame orientation model is established. Secondly, orientation parameters of the auxiliary frame are motion-compensated to achieve a geometric consistency between the adjacent video frames. Finally, all the video frames are geo-coded in object space, and a geo-coded and smooth video can be generated. Results and Conclusions: The experimental results of a set of Zhuhai-1 satellite video frames show that the proposed approach can effectively eliminate the influence of satellite jitter errors and satellite position and attitude errors. Both the interframe geometric accuracy and the video stabilization accuracy achieved by the proposed approach reach better than 0.3 pixels. [ABSTRACT FROM AUTHOR]

Ionosphere is an important part of the near-earth space environment, and it has an important impact on radio communication, satellite navigation and positioning. Therefore, monitoring the ionospheric morphology is helpful to understand the spatiotemporal changes of the ionosphere and predict the ionospheric morphological characteristics. With the development of global navigation satellite system（GNSS）,ionospheric monitoring has become an important research and application direction. This paper systematically introduces the research progress of multidimensional GNSS ionospheric monitoring and its application in related aspects. It mainly includes space-based/ground-based GNSS joint inversion of ionospheric characteristic parameters, tomography inversion of ionospheric three-dimensional structure, ionospheric delay modeling, ionospheric abnormal disturbance monitoring and mechanism cognition. [ABSTRACT FROM AUTHOR]

Deformation monitoring is an important guarantee for the safe operation of water conservancy projects. With the advantages of high precision, all-day and all-climate observation, global satellite navigation system (GNSS) provides new means for deformation monitoring in hydraulic engineering. At present, the deformation monitoring technologies represented by satellite positioning is approaching intelligent development in all processes, all aspects, and all autonomous. Firstly, we focus on the demand of deformation monitoring of water conservancy projects, and review the development of deformation monitoring technology. Then， the application of GNSS deformation monitoring in hydraulic engineering is introduced. Besides, the difficulties and limitations of GNSS deformation monitoring application are discussed. Finally, the development direction of intelligent GNSS deformation monitoring in hydraulic engineering in the future is prospected. [ABSTRACT FROM AUTHOR]

Objectives: The major global navigation satellite system (GNSS) includes global positioning system (GPS), global navigation satellite system (GLONASS), Galileo navigation satellite system (Galileo), and BeiDou navigation satellite system (BDS). The accuracy of broadcast ephemeris of the four major GNSS should be evaluated, and the evaluation results do not include systematic deviations. Methods: We download the mixed broadcast ephemeris and precise ephemeris of the multi ‑ GNSS experiment (MGEX) for a total of 62 days from 1st September to 1st November in 2019, and select healthy satellite data from broadcast ephemeris every 15 minutes. After this preparation, we calculate the satellite position and clock difference of each GNSS system, then compare root mean square (RMS) of orbital position deviation, RMS of clock difference, and RMS of signal‑in‑space range error (SISRE) of all kinds of satellites with precise ephemeris. To correct the position of antenna phase center, the correction value should be selected corresponding to the generation of broadcast ephemeris. To eliminate the systematic deviation of clock difference, we make a quadratic difference on the average value of daily clock difference of single satellite. Results: The radial, along‑track, cross‑track position deviation and clock difference of the four major GNSS broadcast ephemeris fluctuate around 0 scale, indicating that the calculation results do not include systematic deviation, the methods of correcting the position of antenna phase center and eliminating systematic deviation of clock difference are correct and effective. Conclusions: The order of accuracies of the four major GNSS broadcast ephemeris from high to low is Galileo, GPS, BDS, GLONASS. With the development of each navigation system, the accuracy of broadcas ephemeris can be further improved. [ABSTRACT FROM AUTHOR]

Objectives: Network real-time kinematic (RTK) technology can provide real-time and high-precision positioning service for users over the wide range, however, the current technology depends on high density of satellite navigation and positioning (SNAP) reference station network. To satisfy the high-precision positioning requirements based on the sparse reference station network, this paper recommends a net- work RTK service method based on virtual atmosphere constrait (VAC).Methods: Firstly, a non-combined double- difference observation model is constructed to solve and fix the network RTK baseline ambiguity quickly. Then, the baseline atmospheric delay is extracted and the slant path ionosphere and zenith trop- sphere are established respectively. Finally, the interpolated atmospheric delay and its accuracy information are regarded as virtual observations to improve the positioning performance of the terminal RTK. Based on a 205.1 km station spacing SNAP network from a northwest region， China, six rover stations inside and outside the network are used for termininal RTK verification. Results: The results show that the VAC net- work RTK service method can meet the needs of high-precision positioning users over large-scale reference networks. The terminal positioning accuracy and initialization speed by the VAC method are significantly improved by 61.64% and 9.96% compared with the traditional virtual reference station method. In this service mode, the average horizontal and vertical root mean squares of the fixed solution for the six terminals are 1.19 cm and 2.73 cm. Initializing RTK solution by a lot of times, 88.78% of periods can be fixed within 2 epochs for the six rover staions. Conclusions: The VAC service mode has good adaptability to both users inside and outside the large-scale SNAP base station network. [ABSTRACT FROM AUTHOR]

Objectives：The fitting sequence of the traditional grey model (GM) cannot reflect the dynamic change of the stepwise ratio of the modeling data sequence, and the accuracy of the satellite clock offset prediction results need to be improved.Methods：The stepwise ratio sequence of modeling data is proposed as target, and a discrete grey model(DGM) that reflects the trend of the modeling data sequence stepwise ratio is established.The specific steps of the method applied to satellite clock offset prediction are given as well. We first generate a corresponding stepwise ratio sequence for the modeling clock offset sequence. Then, the stepwise ratio sequence is used for DGM modeling and forecasting. Finally, after combining the relationship between the stepwise ratio and the modeled clock offset sequence, the forecast results are restored to obtain the corresponding clock offset prediction evalue. Results：The post‐precision clock offset data provided by iGMAS are used for forecasting experiments, and evaluate the quadratic polynomial model (QPM) and the GM forecast results. The results show that the improved algorithm clock offset prediction accuracy is better than those of the QPM and GM. In the single‐day forecast test, the average accuracy of forecast products obtained by this method.Compared to the QPM results, BeiDou navigation satellite system(BDS) satellites and global positioning system(GPS) satellites are increased by 54.71% and 46.40%, respectively, and compared to the GM results, BDS satellites and GPS satellites are increased by 82.96% and 67.81%, respectively.In the continuous multi‐day forecasting experiment, BDS satellites and GPS satellites are increased by 38.15% and 37.09% compared to the QPM results,respectively, and BDS satellites and GPS satellites are increased by 57.43% and 26.30% compared with the GM results, respectively. Conclusions：The prediction test results verify that the proposed method can predict satellite clock offset with high accuracy and relatively stable performance, and its prediction accuracy and universality are significantly better than the commonly used QPM and GM algorithms. In addition, this method solves the problem that the GM prediction fails when the satellite clock offset stepwise ratio changes drastically, and provides a new idea for high‐precision satellite clock offset prediction. [ABSTRACT FROM AUTHOR]

The successful launch of Chang'E ⁃4 relay satellite in June 2018 has laid a good foundation for the mission of landing on the back of moon at the end of the year. Very long baseline interferometry (VLBI) system plays an important role in satellite positioning and orbital transfer. In this paper, the data accuracy of delay, delay rate and positioning of VLBI observations during the real⁃time phase of the Chang'E⁃4 relay satellite mission are calculated, and the application of positioning reduction in the real⁃time track monitoring of the orbit control arcs of the Chang'E⁃4 relay satellite is presented. In the process of the relay satellite en⁃ tering Halo orbit, we show the real⁃time change of the orbit elements converted by our positioning method and compare the real⁃time positioning results with the post⁃time orbit determination results to further verify the validity and accuracy of our real⁃time positioning results. We provide a new Halo real⁃time track moni⁃ toring method. [ABSTRACT FROM AUTHOR]

Firstly, the influence of the improvement of the BeiDou navigation satellite system(BDS) and GPS satellites visibility using the three low earth orbit (LEO) satellites GRACE ‐ A/B and Fengyun3C (FY3C) is analyzed. Results show that the improvement to BDS medium earth orbit (MEO) satellites is the most significant, with the single coverage increased by 45.7% and quad ‐ coverage increased by 10.7%, which is equivalent to that of GPS satellites. Then, satellite positioning and dilution of precision (SPDOP) is used to analyze the contribution of LEO satellites to enhance the geometry structure in navigation satellite orbit determination. With the enhancement of three LEO satellites, the SPDOP of the BDS geostationary orbit (GEO) satellites, inclined geosynchronous orbit (IGSO)satellites, MEO satellites and GPS satellites are decreased by 49%, 39.8%, 34.9% and 41.2% respectively. The orbit determination experiment based on the observations from seven regional ground observation stations and three LEO satellites are carried out. The results show that one‐dimensional root mean square (1D RMS) of GPS satellites orbit is reduced from 14.4 cm to 10.2 cm, improved by 29.1%. The 1D RMS of BDS GEO,IGSO and MEO satellites in overlapping arcs decrease from 359.8 cm to 90.5 cm, 175.6 cm to 52.1 cm, and 90.5 cm to 30.4 cm, improved by 74.8%,70.3%,and 66% respectively. [ABSTRACT FROM AUTHOR]