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Objectives: Global navigation satellite system (GNSS) coordinate time series provide important data support for the study of crustal movement and deformation, and plate tectonics. Due to the noise caused by various external factors, the GNSS coordinate time series cannot reflect the real motion information of the station well. To effectively reduce the noise in the GNSS time series, we adopted a noise-reduction method combining genetic algorithm (GA) and variational mode decomposition (VMD-GA-VMD). Methods: First, the genetic algorithm was used to optimize VMD parameters, and the envelope entropy of the input signal was used as the fitness function of the genetic algorithm to find the optimal VMD parameter combination suitable for the signal. According to the optimized parameters, the signal was decomposed by VMD to obtain a series of modal components. Then we calculated the multi-scale permutation entropy (MPE) of each component and then regarded the MPE as the criterion of the noise component. Finally, according to the MPE, the noise components were identified and removed, and the remaining components were reconstructed to obtain the noise-reduced signal. In this paper, the noise reduction effect of GAVMD was analyzed through the example of noise reduction of analog signal and observation data, and compared with wavelet denoising (WD) and empirical mode decomposition (EMD) methods. Results: The experiment results show that: (1) The noise reduction results from the analog signals show that WD and EMD have the incomplete and excessive troubles on the noise reduction, respectively. However, GA-VMD can effectively eliminate noise and retain effective signals. From the evaluation index, compared with WD and EMD, the signal-to-noise ratio were increased by 5.18 dB and 2.91 dB, the correlation coefficient by 0.05 and 0.02, respectively, when using GA-VMD. (2) For the complex observation, we used the noise and velocity uncertainty as accuracy indicators to evaluate the noise reduction effects of the three methods. The results show that WD can only extract a part of the white noise, while EMD and GA-VMD can completely remove the white noise. GA-VMD can reduce the flicker noise to the range of 0 to 6 mm/a0.25. For the velocity uncertainty, the average gain rates of GA-VMD relative to the WD and EMD are 69% and 15.33%, respectively. GA-VMD has an average correction rate of 79.89% and 84.46% for the velocity uncertainty and flicker noise of GNSS coordinate time series. Conclusions: Therefore, GA-VMD is the most effective one among the three noise reduction methods, which can effectively reduce the noise in the GNSS time series and improve its accuracy. However, in this paper, we only discussed the effect of GA on VMD parameter optimization without comparing it with other methods. Hence, it will be the key for studying the advantages and shortcomings of those optimization algorithms in the selection of VMD, and improving the accuracy on the GNSS time series in the future. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Harbour Engineering is the property of Editorial Office of China Harbour Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study and expand the application of BeiDou Navigation System in railway engineering survey, the technical advantages of BDS system are used to solve the problem of railway surveying and positioning in mountain areas. Based on a railway in mountain areas, this paper has established a belt-shaped BeiDou continuous operation reference station system (hereinafter referred to as "BeiDou CORS System") and a high-precision location service cloud platform. The domestic multisatellite and multi-frequency survey receiver is used to collect the data of control points. The survey accuracy of RTK observation data of BDS, GPS and GNSS hybrid ephemeris network based on BeiDou CORS System and RTK observation data in the form of traditional base stations are compared respectively. The results show that: (1) The positioning function of network RTK based on railway banded BeiDou high-precision location service cloud platform is stable and reliable; (2) The network RTK measurement method based on the Beidou CORS system only needs to perform elevation surface fitting, and the accuracy of the results collected in 3s can meet the accuracy requirements of the network RTK center line survey, section survey, construction stakeout, and image control survey in the railway survey code. The same type of equipment and the same precision observation method should be used as much as possible to ensure the repeated survey accuracy, and the survey accuracy can also be improved by increasing the observation time and using the existing elevation control points for elevation correction in local areas; (3) The internal coincidence accuracy tolerance of plane and elevation of network RTK survey based on BeiDou CORS System can be set to 1.7 cm and 2 cm, and the outer coincidence accuracy can be set to 2.2 cm and 5 cm. [ABSTRACT FROM AUTHOR]

Objective: Navigation context comprises observation environment and carrier activity. While global navigation satellite system (GNSS) can provide high-precision navigation, positioning, and timing services for users, users can also annotate the types of navigation scenarios they are in by distinguishing the quality and features of terminal observation values. Navigation context clustering is important for adaptive seamless navigation and location services, which can significantly promote context adaptability, configuration flexibility, and system robustness. Methods: In terms of current issues that the division of water/underwater context is simple and has insufficient granularity, the quality and characteristics of GNSS observation signals in different water depth layers are analyzed by collecting GNSS observations in different water regions. Results and Conclusions: The results show that the underwater navigation context has remarkable layering. Considering that the navigation context has inherent properties such as segmentation, merging, and connectivity, this paper subdivides the underwater navigation context into three layers: Submerged water (about less than 6.5 cm), shallow water (about greater than 6.5 cm and less than 8.5 cm), and deep water (about greater than 8.5 cm) through K-means clustering, and conducts navigation context classification experiments using various GNSS signal features. It reveals that the clustering accuracy rate is 90.4%, indicating the effectiveness of submerged-shallow-deep navigation context division. [ABSTRACT FROM AUTHOR]

The existing highway construction monitoring systems are independently deployed. This paper proposes an intelligent monitoring system for highway construction based on remote wide area networks. By employing the tracking devices equipped with inertial measurement units and global positioning systems, the workers' activity space is monitored. People and equipment entering the site are registered by radio frequency identification tags with protective measures. Motion sensors are employed to monitor the changes in scaffolding, building structures, and highway low-grade inclinations. In addition, a light-weight object detection (LOD) algorithm is proposed to detect construction workers who fail to wear safety helmets. The LOD algorithm replaces the standard convolutional networks with depthwise separable convolution networks. It introduces the receptor field module, employs the LOD-NMS algorithm and Mish activation function, and sets an appropriate prior box according to the characteristics and ratios of people's heads in Asia, thus well balancing the precision and prediction efficiency. Experiments are conducted on the WIDER FACE open source data set and the real data sets. The results show LOD algorithm not only detects workers' safety helmets in real time with high precision, but also achieves higher recognition accuracy than traditional algorithms despite the low-resolution input images. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Remote Sensing is the property of Editorial Office of Journal of Remote Sensing & Science Publishing Co. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: Atmospheric water vapor is one of the important components in troposphere. It is of great significance to study the factors and accuracy of influencing water vapor. This paper mainly studies the influencing factors of precipitable water vapor (PWV) in the Loess Plateau and evaluates its actual accuracy. Methods: Firstly, the pressure, temperature data of the fifth-generation atmospheric reanalysis data of EC-MWF (ERA5) and global navigation satellite system (GNSS) derived zenith troposphere delay (ZTD) are evaluated. Secondly, according to the pressure and temperature data of ERA5 and ZTD data of crustal movement observation network of China (CMONOC), the PWV with 1-hour time resolution is calculated, and the theoretical error of PWV is deduced by using error propagation theory, and then the accuracy of PWV in the Loess Plateau is analyzed by comparing with the actual calculation error of PWV. Results: The results show that the average root mean square(RMS) and bias of GNSS-derived ZTD calculated by GAMIT/GLOBK and PANDA are 4.05 mm and −0.46 mm, respectively. The average RMS and bias of ERA5-provided pressure and temperature are 3.36 hPa/1.97 K and − 0.01 hPa/0.04 K, respectively. The theoretical error of PWV in the Loess Plateau is 1.51 mm, and the actual error is 1.94 mm. Conclusions: The accuracy of PWV calculated in this paper is high, which is of great significance to the investigation of water vapor distribution and climate monitoring. [ABSTRACT FROM AUTHOR]

Global navigation satellite system(GNSS)⁃acoustic seafloor positioning is a technology proposed and developed for deformation monitoring of plates in the submarine subduction zone. As an important technology for the construction of marine space time reference network, it has broad application prospects. Although the current research results of GNSS⁃acoustic seafloor positioning cannot meet the construction re⁃quirement of marine space time reference network, its data processing method, especially the fine processing method of sound speed error, has important reference significance for the construction of seafloor part (seafloor geodetic reference station) of marine space time reference network. This paper firstly introduces the origin of GNSS ⁃acoustic seafloor positioning and summarizes it into two categories: Static measurements and dynamic measurements. At the same time, the sound speed error processing method is used as the development line to refine three development stages of the technology: Only assuming the vertical stratification of ocean sound speed, considering the temporal variation of sound speed, and considering the horizontal gradient of sound speed. For the stage of only assuming vertical stratification of ocean sound speed, foreign scholars used geometric structure symmetry to weaken the influence of sound speed error; domestic scholars mainly studied the error sources besides the sound speed (lever arm offset, time tag deviation, attitude angle error, etc.) and used the stochastic model to weaken the influence of system error on the positioning results. For the stage of considering the time⁃domain variation of sound speed, foreign scholars used fitting method (polynomial fitting or cubic spline fitting) combined with parameter smoothing constraint to solve the time⁃domain variation of sound speed, and improve the stability of positioning results. Based on this, domestic scholars have refined the parameter fitting method (considering the variation characteristics of the long period term of parameters). In addition, domestic scholars have proposed the underwater differential positioning algorithm to innovate the seafloor positioning technology. For the stage of considering the sound speed horizontal gradient, scholars have solved the sound speed horizontal gradient parameters in the GNSS⁃acoustic seafloor positioning processing, which improves the stability of the horizontal positioning results, and verified the reliability of the results by using the marine numerical model.This paper presents the prospect of high precision data processing methods of GNSS acoustic seafloor positioning for the seafloor reference station construction, and introduces the concept of small spatial⁃temporal scale sound speed tomography (sound speed error processing method based on ocean positioning reference network) in order to solve the problem that numerical prediction model cannot provide small spatial⁃temporal scale products, so as to provide high⁃precision sound speed error correction services for underwater vehicles. [ABSTRACT FROM AUTHOR]

Soil moisture (SM), as an important component of global water and energy cycles, plays an essential role in the Earth's water cycle, energy balance, and climate change. Traditional field measurement methods for SM are difficult to obtain the spatial distribution of large-scale and long-term SM and have high measurement costs. Microwave remote sensing, with its all-weather and penetrating capabilities, is one of the most effective means of obtaining soil moisture at a large scale and long-term manner, particularly the L-band global navigation satellite system-reflectometry (GNSS-R) technology with advantages of both active and passive microwave remote sensing, which has been paying a lot of attention in SM measurements. Based on the investigation and analysis of domestic and international progress, this paper systematically introduces the principle and characteristics of GNSS-R technology for obtaining SM, and gives the specific steps of SM measurement from both forward and backward retrieval aspects, the main faced difficulties, and key issues to be solved. Taking the latest cyclone GNSS (CYGNSS) satellite estimation as the main part, the theoretical model and method based on CYGNSS SM estimation are deeply expounded. In addition, the opportunities and challenges in the development of GNSS-R SM remote sensing are briefly analyzed, aiming to provide a reference for future ground-based, airborne, and satellite-based GNSS-R SM remote sensing observation and application in China. [ABSTRACT FROM AUTHOR]

Continuous and dense global navigation satellite system (GNSS) observations of surface deformation can be used to recover regional terrestrial water storage (TWS) changes with high spatiotemporal resolution, which is of great significance for the study of regional water cycle and climate changes and has become a hot topic in the field of hydro-geodesy. This paper introduces the basic theory and inversion algorithms of the loading Green's function method and Slepian basis function method, and the stability and performance of these two methods in retrieving regional TWS changes by using GNSS surface deformations are evaluated. Meanwhile, the latest progress in using GNSS-derived TWS changes to study regional water cycles and extreme climate changes is reviewed. The existing problems and future development trends of the inversion of GNSS observations (e. g. refined GNSS data processing and joint inversion of multi-source data) are summarized and analyzed. It provides important insights into the use of GNSS observations to investigate regional TWS changes and related applications in hydro-geodesy. [ABSTRACT FROM AUTHOR]

Objectives: Latest release of international terrestrial reference frame has been generated with an enhanced modeling of nonlinear station motions, while more investigations on the strategies applied for the terrestrial reference frame modeling nonlinear station motions still needed. Methods: A global GPS (global positioning system) network has been reprocessed, using the latest GNSS (global navigation satellite system) data processing models and an integrated strategy, and then accurate and consistent input data are obtained; the post-seismic deformation models of 13 CMONOC (crustal movement observation network of China) stations are established and used as the input data, and FREQ2016 based on the function model, and GFZ2016 and EOST2016 considering the environmental loading correction are realized; these GPS terrestrial reference frames with different models are compared in terms of the goodness for fit, velocities and seasonal signals, and then the optimal model is explored. Results: The results show that the weighted root mean square averages of the postfit residuals of FREQ2016 are smaller than those of GFZ2016 and of EOST2016; FREQ2016 shows more significant seasonal signals, especially for semi-annual signals; the horizontal velocity field differences of these three are almost negligible (<0.08 mm/a), and the large vertical velocity differences, for some stations, reach 1.3 mm/a; the reduction of FREQ2016 horizontal velocity formal errors is about 10%. Conclusions: This paper suggests that the strategy based on the function model is better than that of considering the environmental loading correction. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: Global navigation satellite system (GNSS) technology is widely used in deformation monitoring such as dams, bridges, and landslides. In traditional monitoring methods, the reference stations need to be built, which leads to the increased monitoring cost. Methods: This paper proposes a GNSS deformation monitoring method based on virtual reference station (VRS), which uses the existing continuously operating reference stations (CORS) observation data to generate VRS instead of physical reference station to achieve high accuracy deformation monitoring. Firstly, the existing CORS observation data are used to obtain the atmospheric error correction models and generate VRS. Secondly, the baselines between VRS and each monitoring point are calculated. In order to further improve the accuracy of data processing, Delaunay triangulation networks are formed, and the baseline vector solution results are checked according to the criterion that the triangle closure error is zero. Finally, the checked baseline solution results are adjusted to obtain the final three-dimensional position coordinates of the monitoring points. Results: This paper uses about 30 monitoring points in Pingbian Miao Autonomous County, Yunnan Province for experimental analysis. The results show that the interpolation accuracis of the double-difference tropospheric and ionospheric delay are better than 10 mm if the distance between CORS reference stations is less than 40 km. The observation data longer than 8 hours can realize deformation monitoring with horizontal accuracy better than 5 mm and vertical accuracy better than 10 mm. Conclusions: The proposed method can realize the practical application of landslide monitoring. In the future, we can study how to improve the atmospheric error model and further improve the accuracy of data processing [ABSTRACT FROM AUTHOR]

Copyright of Railway Signalling & Communication Engineering is the property of Railway Signalling & Communication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objective: The research on topography and landform of the Yangtze estuarine waters is of great significance to human social and economic activities such as river management, river construction and water transportation. Establishing an accurate and seamless chart datum and its transformation model with other vertical datums will directly affect the acquisition of high ⁃precision topographic and geomorphic data at the water-land junctions and the unified comprehensive management and analysis. Thus, this paper studies the establishment of seamless chart datum and its transformation model with other vertical datums for estuarine waters, combining with geoid, sea surface topography and three-dimensional numerical simulation of tidal wave motion. Methods: Firstly, the unstructured-grid, finite-volume community ocean model (FVCOM) was used to simulate tidal level and calculate the tidal range at each grid node with the underwater topographic data and the open boundary water level forcing data. According to the correlation between tidal range and chart datum, the chart datum value of each grid node was deduced using tidal range ratios from tide gauge stations with known datums, and a regional seamless chart datum was then established. Secondly, the mean sea surface topography corresponding to a long time scale at each grid node was calculated with the daily sea surface topography product provided by the Copernicus marine environment monitoring service (CMEMS). The mean sea surface topography model was further established by the minimum curvature interpolation. Meanwhile, the geoid in the corresponding area was calculated by the global ultra ⁃high ⁃ order gravity field model Earth gravitational model 2008 (EGM2008) with a spatial resolution of 5′ × 5′. Thirdly, the geoid model was established through bi ⁃ quadratic interpolation. Finally, according to these three constructed models and the geometric relationship of three kinds of vertical datums in space, unification to a consistent spatial resolution was performed and the separation value between chart datum and the ellipsoid reference datum at each grid node was calculated. The vertical datum transformation model be⁃ tween the seamless chart datum and ellipsoid reference datum was established by the minimum curvature interpolation. Results: Using this method, we carried out the experiment at the typical estuarine waters, south branch of the Yangtze Estuary, and established the seamless chart datum and its vertical datum trans⁃ formation model. The global navigation satellite system (GNSS) leveling data from three long-term tide gauge stations were used for verification and accuracy evaluation of the model. The results show that the ab⁃ solute errors of the vertical datum transformation model at these three long-term tide gauge stations were − 19.8 cm, −25.8 cm and −27.0 cm respectively, which were all higher than the evaluated error (12.4 cm) of the model. The main reason is that the Yangtze estuarine waters have complicated tidal wave characteristics and they are nearshore waters, which leads to poor accuracy of the mean sea surface topography model in this region, thus further reducing the accuracy of the transformation model as a whole. Despite this, the accuracy of the transformation model still meets the requirements of International Hydrographic Organization standards for hydrographic surveys. Conclusions: Therefore, the research method of this paper are feasible and reliable, especially in far-sea areas. When the accuracy of satellite altimetry is further improved in the nearshore areas, the proposed method in this paper can be extended to nearshore and inland waters. [ABSTRACT FROM AUTHOR]

Copyright of Ordnance Industry Automation is the property of Editorial Board for Ordnance Industry Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrographic Surveying & Charting / Haiyang Cehui is the property of Hydrographic Surveying & Charting Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Harbour Engineering is the property of Editorial Office of China Harbour Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: On July 31, 2020, China's BeiDou-3 satellite navigation system (BDS-3), which operates independently, has been fully completed and officially opened for service. The signal system of BDS-3 has been redesigned to provide public service signals of five frequencies: B1I, B3I, B1C, B2a and B2b. Methods: Based on the observations of international global navigation system monitoring and assessment service and multi-GNSS experiment (MGEX) tracking stations, this paper analyzes the characteristics of pseudoranges multipath error, signal to noise ratio, geometry-free ionosphere-free phase(GFIFP) combined observations of the new signal system, as well as the precise orbit determination (POD) performance evaluation of BDS-3 satellites. Results and Conclusions: The results show that the multipath noise level of BDS-3 satellites signal is better than that of BeiDou-2 navigation satellite system satellites, and there is no systematic deviation related to altitude angle, B1C is more significantly affected by multipath and noise. The GFIFP sequences of different signal combinations of BDS-3 satellites show periodic systematic error related to satellite, and the peak value is about 2 cm. For BDS-3 satellites, the one-step POD method is used. The two frequencies ionospheric free combination of B1I & B3I and B1C & B2a is adopted respectively. The orbit boundary discontinuity and satellite laser ranging carried out an orbit accuracy check, and the results show that when the number of available observations is less than B1I & B3I, the orbit accuracy of B1C & B2a is equivalent to that of B1I & B3I, and the radial internal coincidence accuracy is 6.1 cm and 6.6 cm respectively. [ABSTRACT FROM AUTHOR]

Objectives: Non-ideality of navigation satellite signals can cause ranging bias between different receivers, which is an important factor that may degrade the accuracy and integrity performance of global navigation satellite system. In civil aviation and other high integrity services, it is necessary to consider the non-ideality characteristics of the signal and define the design constraints of the user receiver, so as to reduce the impact of non-ideality and ensure service safety. Methods: The B1C and B2a signals of BeiDou satellite navigation system (BDS) are planned to join the international civil aviation standard, so it is necessary to study their non-ideality characteristics and define the receiver design constraints. This paper analyzed the non-ideality characteristic of BDS B1C and B2a signals. In order to avoid the influence of noise and multipath, a large aperture antenna was used to collected all the in-orbit satellite broadcasting B1C and B2a signals (including 27 satellites) to obtain pure signal samples. Then, the software receiver was used to process the signal samples under various receiving parameters to obtain the ranging biases under different receiver front-end bandwidth and code discriminator space, and the ranging bias range and variation with the receiving parameters are evaluated. Furthermore, taking the application in dual frequency multi-constellation satellite based augmentation service as an example, the receiver design constraints of the two signals were analyzed. Results and Conclusions: The experimental results show that the range biases introduced by the non-ideality of B1C and B2a signals are less than 0.68 m and 0.44 m, respectively, under the parameters range commonly used by receivers. Under the requirement of range bias less than 0.1 m, the applicable parameter range of receiver design constraints for B1C and B2a signals is better than the relevant requirements of the international civil aviation organization draft standard. There is sufficient margin to further consider other constraints. [ABSTRACT FROM AUTHOR]

Copyright of Industrial Minerals & Processing / Huagong Kuangwu yu Jiagong is the property of Industrial Minerals & Processing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Unmanned Aerial Vehicles (UAV) have widely been served as a new technology in agricultural aviation plant protection and pest control in China. However, it is highly demanded to improve the accuracy of UAV spraying pesticides and operational efficiency. In this study, a Variable Rate Application (VRA) of a centrifugal spraying system was designed for precise placement and timing of pesticide application in specific field conditions using the network Real-Time Kinematic (RTK) technology. STM32F103 single-chip microcomputer was used for the core controller. A serial port of controller was selected to obtain the global position system (GPS) information. A network modular Data Terminal Unit (DTU) was connected to realize the network RTK technology via the serial port of the controller. The control voltage was used to tailor the speeds of the centrifugal nozzle motor and peristaltic pump. A Pulse Width Modulation (PWM) was used to control the output voltage from the core controller to the armature of motors in this system. The speed of the centrifugal nozzle motor determined the output droplet size, while the speed of peristaltic pump determined the flow rate and amount of spray fog. The agricultural dataset before the system working was acquired using the airborne multispectral camera, ground object spectrometer, and handheld GPS. A prescription chart was also constructed using ArcGIS software. In the system working, the GPS modular was used to capture the location longitude and latitude data for the system to read and analyze. The system was always real-time searching the UAV geographical position during the spraying pesticides process using the GPS data, and then matching the position using the orthogonal grid. Meanwhile, the system was used to real-time tailor the changes in the duty cycle of output PWM, after matching the decision of the prescription map. The speeds of the centrifugal nozzle motor and the peristaltic pump were then to control the particle size and application amount of the UAV. The operation data was finally uploaded to the monitoring platform for real-time display and storage. Several spraying experiments were carried out in the research base of South China Agricultural University in Zengcheng City, Guangdong Province of China. The airborne spraying device was carried on the MG-1p plant protection UAV using a developed DJI Drone. The sampling points of droplets were set to match the planting density of crops, where the water-sensitive paper was used to collect the droplet data. After UAV operation, the water sensitive paper was collected into a plastic bag for later use. An hp4678 scanner was selected to map the collected water-sensitive paper after the experiment. A DepositScan software was utilized to analyze the water-sensitive paper in each sampling area after image acquisition. A detailed dataset was obtained, including the deposition amount, coverage density, and particle size of droplets. The data demonstrated that the accuracy of the device was within 0.6 m at the operating speed of 2 m/s. The application effect was finally stabilized within 2.2 m in the case of continuous operation. Particle size varied smoothly in the boundary area of prescription, as the rotating speed of the centrifugal nozzle increased. The findings can provide a sound basis for the improvement of variable application technology of plant protection UAV in precise agriculture. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: As BeiDou satellite navigation system‑3 （BDS‑3） starts to provide service for global users, it is possible to get global‑coverage and all‑time positioning service for space application using BDS alone. The performance of space‑borne BDS positioning is thoroughly analyzed with the broadcast ephemeris and the in‑orbit data of global navigation satellite system occultation sounder (GNOS) aboard FengYun‑3D (FY‑3D) satellite. Methods: Firstly, the visibility and position dilution of precision of BDS satellites in different low‑erath‑orbit （LEO） are calculated based on broadcast ephemeris. Moreover, the orbit, clock error of broadcast ephemeris and signal‑in‑space range error (SISRE) are studied. Secondly, the real visible satellite number, signal strength, precision of pseudo range and position accuracy are verified with the measurement data of GNOS. The code biases of BDS‑2 satellites are focused on. Finally, the total electron content above 836 km LEO orbit is measured using BDS dual‑frequency measurements. Results: The results show that the global coverage usability from ground to 2 000 km height orbit has already been 100%. The mean visible BDS satellite number across the world is 50% larger than that of global positioning system （GPS） . For BDS broadcast ephemeris, the 3D orbit error is 1.5 m and clock error is 2.4 ns. SISRE is about 0.79 m and the clock accuracy of BDS‑3 has reached the same level of GPS. The in‑orbit data results show that GNOS in FY‑3D could get 100% positioning with BDS‑2 signals in service areas, and 3D position accuracy is 5.53 m. All BDS‑2 satellites including geosynchronous earth orbit （GEO）, inclined geosynchronous orbit and medium earth orbit satellites have code biases. As GEO satellite is static relative to ground users, the code biases of GEO is firstly measured directly, in which the maxium code bias can reach about 0.6 m. The total electron content above 836 km can cause relative pseudo range delay of about 0.6 m. Conclusions: The research in this paper verifies the usability and performance of BDS for space‑based users . [ABSTRACT FROM AUTHOR]

Objectives: The position time series of global navigation satellite system (GNSS) contain rich tectonic and non-tectonic deformation information, and the complex components are difficult to accurately model and effectively separate non-tectonic information. It is very important to remove the non-tectonic de‐ formation information for the accurate and effective application of the observation data. Methods: Empirical mode decomposition （EMD） is an adaptive time-frequency processing method to correct the period term of time series at 24 GNSS continuous stations and 2 mobile stations in Sichuan Province and Yunnan Province. Results: The results show that the correction of the period term is necessary, and the EMD method can ex‐ tract the different frequency and amplitude period components adaptively according to its own characteristics of signal at each station. Compared with the original time series, the average root mean square error after correction is reduced significantly in N, E and U directions. And EMD method is more accurate and effective than harmonic model modification. We use the modified continuous station time series to simulate the mobile observations, and find that relatively reliable motion velocities can be obtained after an observation period of 5 ‐6 years. The stability and reliability of EMD method are verified by correcting the period term of the mobile station with the actual continuous observation station at a close distance. Conclusions: This paper provides a reference and theoretical basis for the implementation of mobile GNSS observation and the correction of observation data. [ABSTRACT FROM AUTHOR]

Objectives: BeiDou-3 navigation satellite system (BDS-3) has been fully completed and pro‐ vides reliable positioning, navigation, and timing services to global users. In order to achieve compatibility and interoperability with other global navigation satellite systems (GNSS), B1C and B2a signals have been modulated by BDS-3 based on BDS-2, which enable frequency multiplexing with E1 and E5a signals of Galileo. The inter-system biases (ISBs) are important for the fusion processing of different GNSS. Methods: This paper proposes an ISB estimation and application model based on the single-differenced observations and analyzes the ISBs between the overlapping frequencies of BDS-3 and Galileo. Based on several receivers of the new trackable BDS-3 signals, the characteristics of ISBs between BDS-3 and Galileo are revealed, and the real-time kinematic (RTK) positioning performance of BDS-3 and Galileo is analyzed. Results: The results show that the ISBs of B1C-E1 and B2a-E5a exist in different types of receivers but not in the same type of receivers. In addition, compared with BDS-3-only and Galileo-only, the combination of BDS-3 and Galileo has an improvement of more than 10% in both the success rate of ambiguity resolution and positioning accuracy. Conclusions: The multi-constellation RTK positioning performance with the introduction of ISBs is more advantageous than that of a single constellation [ABSTRACT FROM AUTHOR]

Observation quality is one of the key issues to assess the performances of satellite navigation system. As the main error of positioning and navigation, the multipath delay mitigation has be‐ come the focus of the research in global navigation satellite system. Because the traditional multipath model‐ ling strategy cannot obtain the global optimal solutions, this paper proposes a real-time multipath correction model for BeiDou navigation satellite system (BDS) observation with information constraints. Methods: Firstly, the regularization algorithm combined with total variation term is used to denoise and solve the mul‐ tipath delay series based on the estimated BDS multipath delays. Secondly, the trend and random parts of multipath delays are separately processed and together modelled, in which the strategy of least square plus autoregression is used to estimate model coefficients of multipath delay model by one-step solution. Finally, the multipath mitigation model is further optimized by introducing the estimated model coefficients as the prior information constraints in the BDS real-time applications.Results: The results of real-time experiments of BDS precise point positioning show that, compared with the traditional strategy, the position ac‐ curacy of BDS-2 PPP in east (E), north (N) and up (U) directions can be improved with 10.6%−64.9%, 0.0%−59.1% and 12.6%−67.2% (B1I+B3I), respectively. Moreover, the position accuracy of BDS-3 PPP can be optimized with at least 13.9%, 60.0%, 45.9% (B1I+B3I) and 19.1%, 46.5%, 23.9% (B1C+B2a) in E, N and U directions, respectively. Conclusions: Therefore, the proposed mitigation multipath delays method can significantly improve the BDS observation quality in the BDS real-time positioning services. [ABSTRACT FROM AUTHOR]

The global constellation network of BeiDou-3 navigation satellite system (BDS-3) has been completed, which means that BDS-3 has entered a new era of providing high-quality positioning, navigation and timing service for global users.Methods: To comprehensively compare the performance of BDS-3 uncombined precise point positioning (PPP) with other global navigation satellite systems (GNSS), this paper focuses on three aspects, including the consistency of BDS-3 precise orbit and clock products among different analysis centers, the satellite availability of BDS-3/GNSS, the positioning performance of BDS-3/GNSS single-system and multi-system PPP.Results: Based on the precise orbit and clock products from five analysis centers, the three-dimensional root mean square error of BDS-3 static PPP is between 2.31 cm and 4.00 cm, and its convergence time is significantly slower than that of other GNSS. The intro‐ duction of GPS observations can achieve the most obvious improvement among BDS-3/GNSS dual-system joint PPP. Besides, the quad-constellation observations can effectively shorten the convergence time of PPP and improve the positioning accuracy on kinematic mode. Conclusions: With the development of BDS-3 and the improvement of its orbit and clock products, BDS-3 has a great potential to provide highquality positioning services as other GNSS. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Nonferrous Metals (Mining Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Guangdong University of Technology is the property of Journal of Guangdong University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]