Several noteworthy breakthroughs have been made with the BeiDou Navigation Satellite System (BDS) and other global navigation satellite systems as well as the associated augmentation systems, such as the commissioning of the BDS-3 preliminary system and the successful launch of the first BDS-3 GEO satellite which carries the satellitebased augmentation payload. Presently, BDS can provide basic services globally, and its augmentation system is also being tested. This paper gives an overview of BDS and satellite navigation augmentation technologies. This overview is divided into four parts, which include the system segment technologies, satellite segment technologies, propagation segment technologies, and user segment technologies. In each part, these technologies are described from the perspectives of preliminary information, research progress, and summary. Moreover, the significance and progress of the BeiDou Satellite-based Augmentation System (BDSBAS), low earth orbit augmentation, and the national BeiDou ground-based augmentation system are presented, along with the airborne-based augmentation system. Furthermore, the conclusions and discussions covering popular topics for research, frontiers in research and development, achievements, and suggestions are listed for future research.
The navigation and localization of autonomous underwater vehicles (AUVs) in seawater are of the utmost importance for scientific research, petroleum engineering, search and rescue, and military missions concerning the special environment of seawater. However, there is still no general method for AUVs navigation and localization, especially in the featureless seabed. The reported approaches to solving AUVs navigation and localization problems employ an expensive inertial navigation system (INS), with cumulative errors and dead reckoning, and a high-cost long baseline (LBL) in a featureless subsea. In this study, a simultaneous localization and mapping (AMB-SLAM) online algorithm, based on acoustic and magnetic beacons, was proposed. The AMB-SLAM online algorithm is based on multiple randomly distributed beacons of low-frequency magnetic fields and a single fixed acoustic beacon for location and mapping. The experimental results show that the performance of the AMB-SLAM online algorithm has a high robustness. The proposed approach (the AMB-SLAM online algorithm) provides a low-complexity, low-cost, and high-precision online solution to the AUVs navigation and localization problem in featureless seawater environments. The AMB-SLAM online solution could enable AUVs to autonomously explore or autonomously intervene in featureless seawater environments, which would enable AUVs to accomplish fully autonomous survey missions.
Abnormal value of the multibeam echosounder system is the main influencing factor of accuracy of hydrographic survey and mapping accuracy of seabed topography. Good functional and stochastic models for multibeam bathymetric data processing are necessary to protect accurate display of multibeam bathymetric data in seabed and safety navigation of ships. This study proposed a robust least square collocation method based on the improved multi-quadric function to represent the variation trend of seabed topography accurately and disclose the real seabed topography along with the systematic and random problems of nonsteady multibeam bathymetric data of seabed topography. Fitting methods of seabed topography trend surface and the elimination of trend items were analyzed. The solving method of the empirical covariance function in the least square collocation and the method to eliminate abnormal values in multibeam bathymetric data were proposed. Validity of the proposed method was proved by an experiment. Results demonstrate that the fitted trend terms in the improved multi-quadric function can reflect the overall trend changes of the study area effectively. The applied robust least square collocation method can effectively reflect the systematicness and randomness of nonsteady bathymetric data of seabed topography. This method can overcome the influences of gross errors or abnormal points on the multibeam bathymetric data and can thus increase the accuracy of the estimation points. Compared with the traditional quadratic polynomial surface fitting method, the proposed method is superior in reflecting the overall trend changes in seabed topography, quality of multibeam bathymetric data, and mapping accuracy of seabed topography. This study can increase the detection capacity and effects of seabed topography at a high working efficiency and lay foundations for scientific research and marine exploration in the future.
First, in the first paragraph of this article, the sentence “In recent years, China has been actively promoting the construction and development of the BeiDou Navigation Satellite System (BDS), and by the end of the year 2000 the construction of BDS-1 was complete and BDS-1 began to provide GPS services for China.” should be changed into “In recent years, China has been actively promoting the construction and development of the BeiDou Navigation Satellite System (BDS), and by the end of the year 2000 the construction of BDS-1 was completed and BDS-1 began to provide services for China.” The word “GPS” should be removed.
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