Current Issue : July-September Volume : 2025 Issue Number : 3 Articles : 5 Articles
This study proposes an ultra-wideband (UWB) handover system that increases the range of UWB positioning for bridge inspection using an unmanned aerial vehicle (UAV). A bipartite graph and a greedy algorithm are used, and the problem is transformed into vertex coloring to address the challenge of a large number of anchors and insufficient anchor IDs because the area is long and there are numerous beams and columns under the bridge. Simulation and experiment show that the solution reduces the number of anchors that are required from 27 to 14, which significantly saves deployment costs and reduces power consumption....
Global Navigation Satellite System–Acoustic ranging (GNSS-A) technology can achieve centimeter-level seafloor positioning. However, the horizontal gradient of ocean sound speed limits the seafloor positioning accuracy of GNSS-A. This paper evaluates the impact of ocean sound speed horizontal gradients on GNSS-A seafloor positioning utilizing Bayesian estimation. Publicly available GNSS-A datasets from 2012 to 2021 were processed using strategies with and without estimating sound speed horizontal gradients. The comparison of results demonstrates that the ocean sound speed horizontal gradient has a significant impact on horizontal positioning but a smaller impact on vertical positioning. The mean root mean square (RMS) of horizontal positioning differences for both strategies is 0.12 m, with a maximum of 0.19 m. The mean RMS of vertical positioning differences is 0.014 m, with a maximum of 0.021 m. The mean RMS of station velocity differences is 0.004 m/a and 0.008 m/a in the east and the north components, respectively, with a maximum RMS of 0.01 m/a in the horizontal component. The vertical station velocity differences for both strategies are relatively small, with a mean RMS of 0.002 m/a and a maximum RMS of 0.003 m/a. The mean RMS difference in sound speed correction for both strategies is 0.01 m/s. The sound speed horizontal gradient is larger in the shallow portion than in the deep portion. In the shallow portion, the mean RMS is 0.052 m/s/km and 0.072 m/s/km in the east and north component, respectively. In the deep portion, the mean RMS is 0.023 m/s/km and 0.024 m/s/km in the east and north components, respectively. The sound speed horizontal gradient varies significantly at different locations due to the marine environment discrepancies, which require refined GNSS-A processing to improve seafloor positioning accuracy....
Global Navigation Satellite Systems (GNSSs) provide free services such as the Galileo High-Accuracy Service (HAS) to enhance navigation precision. The Joint Research Centre (JRC) developed a monitoring system for HAS corrections from Galileo signals and the internet, comparing them with Multi-GNSS Experiment (MGEX) products. HAS is also exploited to compute daily position and timing solutions of IGS stations and JRC receivers. Performance is evaluated by analyzing HAS ephemeris errors and positioning accuracy considering single- and dual-constellation modes. Signal-in-space and Internet data distribution HAS corrections, their streams, and the derived experimental HAS products are stored at the JRC and made available for research....
This work presents an algorithm to perform autonomous navigation in spacecraft using onboard magnetometer data during GPS outages. An Extended Kalman Filter (EKF) exploiting magnetic field measurements is combined with a Single-Hidden-Layer Feedforward Neural Network (SLFN) trained via the Extreme Learning Machine to improve the accuracy of the state estimate. The SLFN is trained using GPS data when available and predicts the state correction to be applied to the EKF estimates. The CHAOS-7 magnetic field model is used to generate the magnetometer measurements, while a 13th-order IGRF model is exploited by the EKF. Tests on simulated data showed that the algorithm improved the state estimate provided by the EKF by a factor of 2.4 for a total of 51 days when trained on 5 days of GPS data....
In deep space exploration tasks, owing to the dissimilar lighting environment between outer space and Earth ground, the integration time of the navigation camera needs to be evaluated during its design or mission execution. This article puts forward an integration time analysis approach based on computer graphics simulation technology, which is capable of analyzing the rational integration time range in accordance with diverse environments and tasks. Our method encompasses two pipelines: “radiometric calibration” and “scene simulation”. The scene simulation pipeline can simulate the image of the camera in the virtual scene based on the coefficients obtained from radiometric calibration. In contrast to previous methods, the evaluation process proposed in this article is able to simulate different task scenarios and conduct “one-case-one-meeting” analyses for different mission objectives and instrumentations....
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