Spatial linear features are often represented as a series of line segments joined by measured endpoints in surveying and geographic information science. There are not only the measuring errors of the endpoints but also the modeling errors between the line segments and the actual geographical features. This paper presents a Brownian bridge error model for line segments combining both the modeling and measuring errors. First, the Brownian bridge is used to establish the position distribution of the actual geographic feature represented by the line segment. Second, an error propagation model with the constraints of the measuring error distribution of the endpoints is proposed. Third, a comprehensive error band of the line segment is constructed, wherein both the modeling and measuring errors are contained. The proposed error model can be used to evaluate line segments’ overall accuracy and trustability influenced by modeling and measuring errors, and provides a comprehensive quality indicator for the geospatial data.
Any single Positioning, Navigation and Timing (PNT) technology has its vulnerability and limits, even the powerful Global Navigation Satellite System (GNSS) is no exception. To provide continuous and reliable PNT information to users, the theory and technique of comprehensive PNT information system and resilient PNT application system have attracted great attention from Chinese scholars. We try to summarize the progress and development of the synthetic PNT system, including the proposal, the modification and the improvement of the comprehensive PNT, as well as the follow-up resilient PNT. The frame of China’s comprehensive PNT system consisted of comprehensive PNT infrastructure and comprehensive PNT application system is initially described; the achievements on some main PNT technologies are introduced; the conceptual models of resilient PNT are given; besides, existing researches on resilient function models and stochastic models are summarized according to different user scenarios.
Geodetic functional models, stochastic models, and model parameter estimation theory are fundamental for geodetic data processing. In the past five years, through the unremitting efforts of Chinese scholars in the field of geodetic data processing, according to the application and practice of geodesy, they have made significant contributions in the fields of hypothesis testing theory, un-modeled error, outlier detection, and robust estimation, variance component estimation, complex least squares, and ill-posed problems treatment. Many functional models such as the nonlinear adjustment model, EIV model, and mixed additive and multiplicative random error model are also constructed and improved. Geodetic data inversion is an important part of geodetic data processing, and Chinese scholars have done a lot of work in geodetic data inversion in the past five years, such as seismic slide distribution inversion, intelligent inversion algorithm, multi-source data joint inversion, water reserve change and satellite gravity inversion. This paper introduces the achievements of Chinese scholars in the field of geodetic data processing in the past five years, analyzes the methods used by scholars and the problems solved, and looks forward to the unsolved problems in geodetic data processing and the direction that needs further research in the future.
Coastal subsidence monitoring typically employs Global Navigation Satellite System (GNSS) positioning technology. This method provides information only about subsidence below the station base. Sediments in coastal areas tend to accumulate quickly, and subsidence can change significantly due to compaction and alluvium. Therefore, monitoring subsidence above the base is essential to obtain overall coastal subsidence. A new technology called GNSS-Interferometric Reflectometry (GNSS-IR) has been recently developed, which can utilize multipath effects to monitor reflector height. Since the base of the GNSS station is deep and the base length remains constant, the height changes measured by the GNSS-IR technology can reflect subsidence above the base. Accordingly, this paper employs GNSS-IR technology to measure subsidence changes above the base. Additionally, GNSS positioning technology is used to obtain subsidence changes below the base, and the overall subsidence change is then calculated using both GNSS-IR and GNSS positioning technology. The Mississippi River Delta, known for its significant sediment thickness, was selected as the study area, and data from FSHS, GRIS, and MSIN stations was analyzed. The results demonstrate that GNSS-IR can be used to measure the subsidence rate above the base, and the corrected overall subsidence rate is equivalent to the relative sea level rise rate.
With the continuous improvement of the performance and the increasing variety of optical mapping and remote sensing satellites, they have become an important support for obtaining global accurate surveying and mapping remote sensing information. At present, optical mapping and remote sensing satellites already have sub-meter spatial resolution capabilities, but there is a serious lag problem in mapping and remote sensing information services. It is urgent to develop intelligent mapping and remote sensing satellites to promote the transformation and upgrading to real-time intelligent services. Firstly, based on the three imaging systems of the optical mapping and remote sensing satellites and their realization methods and application characteristics, this paper analyzes the applicable system of the intelligent mapping and remote sensing satellites. Further, according to the application requirements of real-time, intelligence, and popularization, puts forward the design concept of integrated intelligent remote sensing satellite integrating communication, navigation, and remote sensing and focuses on the service mode and integrated function composition of intelligent remote sensing satellite. Then expounds on the performance and characteristics of the Luojia-3 01 satellite, a new generation of intelligent surveying and mapping remote sensing scientific test satellite. And finally summarizes and prospects the development and mission of intelligent mapping remote sensing satellites. Luojia-3 01 satellite integrates remote sensing and communication functions. It explores an efficient and intelligent service mode of mapping and remote sensing information from data acquisition to the application terminal and provides a real service verification platform for on-orbit processing and real-time transmission of remote sensing data based on space-ground internet, which is of great significance to the construction of China’s spatial information network.
The high-precision terrestrial reference frame, as the spatial benchmark for geodesy, is an important national infrastructure. However, due to the influence of nonlinear factors related to geophysical phenomena, the overall maintenance accuracy of the ITRF framework is still at the centimeter level. Therefore, accurately characterizing the true trajectories of linear motion, nonlinear motion, and geocentric motion of the reference station is the key to achieve the construction and maintenance technology of a millimeter level terrestrial reference framework. Based on long-term global and regional GNSS observation data, more Chinese geodesy scientists devoted much efforts to the maintenance of millimeter-level geodetic reference framework. The main contributions of this work included the followings: ①Dynamic maintenance of millimeter-level terrestrial reference frame;②Research progress on the method of maintenance of regional reference frame based on GNSS; ③The progress of CGCS2000 frame maintenance in millimeter level accuracy; ④Reprocessing and reanalysis of two-decade GNSS observation in continental China; ⑤Research on current GNSS velocity field model and deformation in Chinese mainland; ⑥The preliminary realization and evaluation of CTRF2020.
As an essential component of future comprehensive Positioning, Navigation, and Timing (PNT) system, indoor positioning technology has extensive application demands, making it a focal point of attention in both academia and industry. This article comprehensively reviews the research status of indoor positioning technology in China, with a focus on highlighting representative achievements and application validations from major research institutions in recent years. It addresses the challenges and issues faced in promotion and application of large-scale, high-precision indoor positioning. Furthermore, a universal and seamless indoor-outdoor positioning system architecture is proposed, along with a technical roadmap and key technologies to achieve this architecture. Finally, an analysis and outlook on future technological trends are presented.
At present, GNSS-Acoustic (GNSS-A) combined technology is widely used in positioning for seafloor geodetic stations. Based on Sound Velocity Profiles (SVPs) data, the equal gradient acoustic ray-tracing method is applied in high-precision position inversion. However, because of the discreteness of the SVPs used in the forementioned method, it ignores the continuous variation of sound velocity structure in time domain, which worsens the positioning accuracy. In this study, the time-domain variation of Sound Speed Structure (SSS) has been considered, and the cubic B-spline function is applied to characterize the perturbed sound velocity. Based on the ray-tracing theory, an inversion model of “stepwise iteration & progressive corrections” for both positioning and sound speed information is proposed, which conducts the gradual correction of seafloor geodetic station coordinates and disturbed sound velocity. The practical data was used to test the effectiveness of our method. The results show that the Root Mean Square (RMS) errors of the residual values of the traditional methods without sound velocity correction, based on quadratic polynomial correction and based on cubic B-spline function correction are 1.43ms, 0.44ms and 0.21ms, respectively. The inversion model with sound velocity correction can effectively eliminate the systematic error caused by the change of SSS, and significantly improve the positioning accuracy of the seafloor geodetic stations.
Gravity field is the most basic physical field generated by the material properties of the Earth system. It reflects the spatial distribution, movement and change of materials determined by the interaction and dynamic process inside the Earth. Over the years, a variety of technical means have been used to detect the Earth’s gravity field and supported numerous studies on the global change, resource detection, geological structure movement, water resources change and other related fields of research. Here is part of the progress in surface and marine gravimetry obtained by Chinese geodesy scientists from 2019 to 2023 from the following aspects, including: ① Continuous gravity network in Chinese mainland; ② Application of superconducting gravity measurement; ③ Network adjustment for continental-scale gravity survey campaign and data quality control; ④ Regional time-variable gravity field and its application; ⑤ Research progress on novel technologies for gravity inversion; ⑥ Research progress on marine gravity field determination; ⑦ Application research on marine gravity field.
Modern geodetic technologies, including high-precision ground-based gravity measurements, satellite gravimetry, satellite altimetry, Global Navigation Satellite Systems (GNSS), and Interferometric Synthetic Aperture Radar(InSAR), offer a wealth of observations for monitoring global hydrological processes with exceptional accuracy and spatio-temporal resolutions. Mass redistribution and Earth’s surface deformation over land related to global and regional water cycling can be inferred from modern gravimetry, altimetry, GNSS, and InSAR techniques. Hydrogeodesy becomes an emerging field of geodesy aiming to analyze the changes of water in the Earth system. The paper introduces the China’s advances in hydrogeodesy in recent years. It brings together multiple geodetic teams’ work from China, showcasing the application of modern geodetic technologies in the field of hydrology, including research on terrestrial water storage, groundwater storage, glaciers/ice sheets, and reservoir water storage.
As one of the Analysis Centers (AC) of the International GNSS Service (IGS), Wuhan University (WHU) has been contributing to the IGS by providing ultra-rapid as well as rapid orbit and clock solutions for the established GPS and GLONASS since 2012. In the same year, the IGS initiated the Multi-GNSS Experiment (MGEX) to support the analysis of the emerging GNSS systems and prepare the IGS for Multi-GNSS, which includes GPS, GLONASS, the European Galileo system, the Chinese Beidou Navigation Satellite System (BDS), the Japanese Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigation Satellite System (IRNSS/NaVIC). The major products, i.e., orbits, Earth Orientation Parameters (EOPs), satellite clock as well as attitude have also been provided by WHU since 2012. More recently, WHU has engaged the third reprocessing of IGS for generating the highly accurate station coordinates as inputs for establishment of the International Terrestrial Reference Frame (ITRF) 2020 during 2019—2020. This article presents the recent major advancements of the IGS AC at Wuhan University, including precise products, real-time products, bias products, antenna phase center calibration, and the non-linear motion modeling for GNSS Reference Stations.
Global Navigation Satellite System (GNSS) can provide all-weather, all-time, high-precision positioning, navigation and timing services, which plays an important role in national security, national economy, public life and other aspects. However, in environments with limited satellite signals such as urban canyons, tunnels, and indoor spaces, it is difficult to provide accurate and reliable positioning services only by satellite navigation. Multi-source sensor integrated navigation can effectively overcome the limitations of single-sensor navigation through the fusion of different types of sensor data such as Inertial Measurement Unit (IMU), vision sensor, and LiDAR, and provide more accurate, stable and robust navigation information in complex environments. We summarizes the research status of multi-source sensor integrated navigation technology, and focuses on the representative innovations and applications of integrated navigation and positioning technology by major domestic scientific research institutions in China during 2019—2023.
With the development of Global Navigation Satellite Systems (GNSS), geodetic GNSS receivers have been utilized to monitor sea levels using GNSS-Interferometry Reflectometry (GNSS-IR) technology. The multi-mode, multi-frequency signals of GPS, GLONASS, Galileo, and Beidou can be used for GNSS-IR sea level retrieval, but combining these retrievals remains problematic. To address this issue, a GNSS-IR sea level retrieval combination system has been developed, which begins by analyzing error sources in GNSS-IR sea level retrieval and establishing and solving the GNSS-IR retrieval equation. This paper focuses on two key points: time window selection and equation stability. The stability of the retrieval combination equations is determined by the condition number of the coefficient matrix within the time window. The impact of ill-conditioned coefficient matrices on the retrieval results is demonstrated using an extreme case of SNR data with only ascending or descending trajectories. After determining the time window and removing ill-conditioned equations, the multi-mode, multi-frequency GNSS-IR retrieval is performed. Results from three International GNSS Service (IGS) stations show that the combination method produces high-precision, high-resolution, and high-reliability sea level retrieval combination sequences.
Deep learning based methods have been successfully applied to semantic segmentation of optical remote sensing images. However, as more and more remote sensing data is available, it is a new challenge to comprehensively utilize multi-modal remote sensing data to break through the performance bottleneck of single-modal interpretation. In addition, semantic segmentation and height estimation in remote sensing data are two tasks with strong correlation, but existing methods usually study individual tasks separately, which leads to high computational resource overhead. To this end, we propose a Multi-Task learning framework for Multi-Modal remote sensing images (MM_MT). Specifically, we design a Cross-Modal Feature Fusion (CMFF) method, which aggregates complementary information of different modalities to improve the accuracy of semantic segmentation and height estimation. Besides, a dual-stream multi-task learning method is introduced for Joint Semantic Segmentation and Height Estimation (JSSHE), extracting common features in a shared network to save time and resources, and then learning task-specific features in two task branches. Experimental results on the public multi-modal remote sensing image dataset Potsdam show that compared to training two tasks independently, multi-task learning saves 20% of training time and achieves competitive performance with mIoU of 83.02% for semantic segmentation and accuracy of 95.26% for height estimation.
The exploration of building detection plays an important role in urban planning, smart city and military. Aiming at the problem of high overlapping ratio of detection frames for dense building detection in high resolution remote sensing images, we present an effective YOLOv3 framework, corner regression-based YOLOv3 (Correg-YOLOv3), to localize dense building accurately. This improved YOLOv3 algorithm establishes a vertex regression mechanism and an additional loss item about building vertex offsets relative to the center point of bounding box. By extending output dimensions, the trained model is able to output the rectangular bounding boxes and the building vertices meanwhile. Finally, we evaluate the performance of the Correg-YOLOv3 on our self-produced data set and provide a comparative analysis qualitatively and quantitatively. The experimental results achieve high performance in precision (96.45%), recall rate (95.75%), F1 score (96.10%) and average precision (98.05%), which were 2.73%, 5.4%, 4.1% and 4.73% higher than that of YOLOv3. Therefore, our proposed algorithm effectively tackles the problem of dense building detection in high resolution images.
GF-14 satellite is a new generation of sub-meter stereo surveying and mapping satellite in China, carrying dual-line array stereo mapping cameras to achieve 1:10000 scale topographic mapping without Ground Control Points (GCPs). In fact, space-based high-precision mapping without GCPs is a challenging task that depends on the close cooperation of several payloads and links, of which on-orbit geometric calibration is one of the most critical links. In this paper, the on-orbit geometric calibration of the dual-line array cameras of GF-14 satellite was performed using the control points collected in the high-precision digital calibration field, and the calibration parameters of the dual-line array cameras were solved as a whole by alternate iterations of forward and backward intersection. On this basis, the location accuracy of the stereo images using the calibration parameters was preliminarily evaluated by using several test fields around the world. The evaluation result shows that the direct forward intersection accuracy of GF-14 satellite images without GCPs after on-orbit geometric calibration reaches 2.34 meters (RMS) in plane and 1.97 meters (RMS) in elevation.
With the continued development of multiple Global Navigation Satellite Systems (GNSS) and the emergence of various frequencies, UnDifferenced and UnCombined (UDUC) data processing has become an increasingly attractive option. In this contribution, we provide an overview of the current status of UDUC GNSS data processing activities in China. These activities encompass the formulation of Precise Point Positioning (PPP) models and PPP-Real-Time Kinematic (PPP-RTK) models for processing single-station and multi-station GNSS data, respectively. Regarding single-station data processing, we discuss the advancements in PPP models, particularly the extension from a single system to multiple systems, and from dual frequencies to single and multiple frequencies. Additionally, we introduce the modified PPP model, which accounts for the time variation of receiver code biases, a departure from the conventional PPP model that typically assumes these biases to be time-constant. In the realm of multi-station PPP-RTK data processing, we introduce the ionosphere-weighted PPP-RTK model, which enhances the model strength by considering the spatial correlation of ionospheric delays. We also review the phase-only PPP-RTK model, designed to mitigate the impact of unmodelled code-related errors. Furthermore, we explore GLONASS PPP-RTK, achieved through the application of the integer-estimable model. For large-scale network data processing, we introduce the all-in-view PPP-RTK model, which alleviates the strict common-view requirement at all receivers. Moreover, we present the decentralized PPP-RTK data processing strategy, designed to improve computational efficiency. Overall, this work highlights the various advancements in UDUC GNSS data processing, providing insights into the state-of-the-art techniques employed in China to achieve precise GNSS applications.
Total Electron Content (TEC) and electron density enhancement were observed on the day before 17 March 2015 great storm in the China Region. Observations from ground- and space-based instruments are used to investigate the temporal and spatial evolution of the pre-storm enhancement. TEC enhancement was observed from 24°N to 30°N after 10:00 UT at 105°E, 110°E and 115°E longitudes on March 16. The maximum magnitude of TEC enhancement was more than 10 TECU and the maximal relative TEC enhancement exceeded 30%. Compared with geomagnetic quiet days, the electron density of Equatorial Ionization Anomaly (EIA) northern peak from Swarm A/C satellites on March 16 was larger and at higher latitudes. NmF2 enhanced during 11:30—21:00 UT at Shaoyang Station and increased by 200% at ~16:00 UT. However, TEC and electron density enhancement were not accompanied by a significant change of hmF2. Most research has excluded some potential mechanisms as the main driving factors for storm-time density enhancements by establishing observational constraints. In this paper, we observed pre-storm enhancement in electron density at different altitudes and Equatorial Electrojet (EEJ) strength results derived from ground magnetometers observations suggest an enhanced eastward electric field from the E region probably played a significant role in this event.
In the construction and maintenance of particle accelerators, all the accelerator elements should be installed in the same coordinate system, only in this way could the devices in the actual world be consistent with the design drawings. However, with the occurrence of the movements of the reinforced concrete cover plates at short notice or building deformations in the long term, the control points upon the engineering structure will be displaced, and the fitness between the subnetwork and the global control network may be irresponsible. Therefore, it is necessary to evaluate the deformations of the 3D alignment control network. Different from the extant investigations, in this paper, to characterize the deformations of the control network, all of the congruent models between the points measured in different epochs have been identified, and the congruence model with the most control points is considered as the primary or fundamental model, the remaining models are recognized as the additional ones. Furthermore, the discrepancies between the primary S-transformation parameters and the additional S-transformation parameters can reflect the relative movements of the additional congruence models. Both the iterative GCT method and the iterative combinatorial theory are proposed to detect multiple congruence models in the control network. Considering the actual work of the alignment, it is essential to identify the competitive models in the monitoring network, which can provide us a hint that, even the fitness between the subnetwork and the global control network is good, there are still deformations which may be ignored. The numerical experiments show that the suggested approaches can describe the deformation of the 3D alignment control network roundly.
The satellite gravimetry technology effectively recovers the global Earth’s gravity field. Since 2000s, HL-SST satellite CHAMP, LL-SST satellite GRACE, Gravity Gradient Measurement (GGM) satellite GOCE have been launched successfully, producing some Earth’s gravity models solely from satellites data. However, the space and time resolution of the Earth’s gravity fields do not adequately satisfy scientific objectives. The main reason is that the gravimetry satellites are not enough and observation data insufficient. The paper outlines the current and future status of Chinese gravity satellite missions. The Chinese gravimetry satellite system, named Chinese Gravimetry augment and Mass change exploring mission (ChiGaM), successfully launched in Dec. 2021 after four years of production and over a year of calibration and valiation. The accelerometer, K-band ranging system and the three stellar sensors, among others, were precisely calibrated and trimmed. The satellite mass center was determined and coordinated with the proof center of accelerometer with an accuracy 100μm. The inter-satellite ranging system and BDS/GPS receiver operate together seamlessly. The range and range rate noise is less than 3μm/Hz1/2 and 1μm/s/Hz1/2, respectively, in band of 0.025~0.1Hz. The electrostatic suspension accelerometer is working well. Its high-sensitive axis noise level is 3×10-10 m/s2/Hz1/2 near the frequency 0.1Hz, and 1×10-9 m/s2/Hz1/2 for the less-sensitive axis. Meanwhile the BDS/GPS receiver is used to achieve data for precise orbit determination, yielding an orbit result with accuracy better than 2cm. When compared with KBR observations, the RMS of the bias is less than 1mm. Besides above mission, next gravimetric satellite is being developed now. TQ-2 mission is designed as a totally experimental satellite for gravitational wave detection at low Earth orbit, which can detect the Earth’s gravity field simultaneously. The Bender-type mission is considered the most promising configuration for TQ-2 and consists of two polar satellites and two inclined satellites. Due to the extra observations at the east-west direction derived from the inclined satellite pair, significant improvements has been made in detecting temporal signals with higher accuracy and spatial-temporal resolution. To achieve the scientific goal, the ACC MBW can shift from 0.001~0.1Hz to 0.004~0.1Hz for ACC, and the LRI MBW can shift from 0.01~1Hz to 0.1~1Hz. For future research, a gravimetric potential survey using cold-atomic-clock based on the general relativity theory, cold atom gradiometer should be pursued. Gravimetric technologies should be mined and researched, and the gravimetry satellite constellation should be developed, so as to improve the time resolution and space resolution for meeting the requirements of geophysics, geodesy, earthquake, water resources environment, oceanography, etc.
The contribution presents the representative research progress on global static gravity field modeling, regional geoid/quasigeoid determination, vertical datum study, as well as the theory, algorithm and software for gravity field study in China from 2019 to 2023, which are the highlights of the chapter 6 “Progress in Earth Gravity Model and Vertical Datum” in the “2019—2023 China National Report on Geodesy” that submitted to the International Association of Geodesy(IAG). In addition, suggestions are proposed to promote the research in the fields of earth gravity field, geoid/quasigeoid and vertical datumin China according to trends of international geodesy and related disciplines.
The semantic segmentation methods based on CNN have made great progress, but there are still some shortcomings in the application of remote sensing images segmentation, such as the small receptive field can not effectively capture global context. In order to solve this problem, this paper proposes a hybrid model based on ResNet50 and swin transformer to directly capture long-range dependence, which fuses features through Cross Feature Modulation Module(CFMM). Experimental results on two publicly available datasets, Vaihingen and Potsdam, are mIoU of 70.27% and 76.63%, respectively. Thus, CFM-UNet can maintain a high segmentation performance compared with other competitive networks.
Aerospace surveying and mapping has become the main method of global earth observation. It can be divided into the geodetic observation satellites and the topographic surveying satellites according to the disciplines. In this paper, the geodetic satellites and photographic satellites are introduced respectively. Then, the existing problems in Chinese earth observation satellites are analyzed, and the comprehensive satellite with integrated payloads, the intensive microsatellite constellation and the intelligent observation satellite are proposed as three different development ideas for the future earth observation satellites. The possibility of the three ideas is discussed in detail, as well as the related key technologies.
The Global Positioning System (GPS) is a GNSS constellation, but GNSS is not always GPS. GPS is one of the GNSS constellations used around the world. The GNSS constellations include GPS (US), QZSS (Japan), Beidou/BDS (China), Galileo (EU), and GLONASS (Russia). In 1999, the European Commission (EC) proposed the European Galileo satellite navigation system for the first time. A four-phase development was proposed, including public and private sector finance. Galileo was intended for both civilian and government use, and is managed and controlled by civil authorities. Galileo is made up of 30 satellites, a number of globally distributed ground stations, and a ground control and monitoring system, all of which are extremely similar to the structure, format, and layout of GPS. In this study, we investigate GPS/GLONASS/Galileo/Beidou/IRNSS/QZSS Navigation Satellite System integration algorithm for long baselines ranging from 1500km to 3000km in China, Japan and Mongolia. The positioning performance with GPS/GLONASS/Galileo/BDS/IRNSS/QZSS, GPS-only, Galileo-only, GLONASS-only and BDS-only, etc. is compared in terms of the positioning accuracy. An improvement of positioning accuracy over long baselines can be found with GPS/GLONASS/Galileo/BDS/QZSS/IRNSS compared with that of GPS-only and that of BDS-only. The obtained differences of the two baselines (Topcon Magnet Tools Software (Multi-GNSS)-(CSRS-PPP (GPS/GLONASS), (Trimble-RTX (GPS/GLONASS), (AUSPOS (GPS/GLONASS)) Online Processing Software) by using GPS/GLONASS/Galileo/BDS/QZSS/IRNSS signals is between 40cm and 111.5cm on three days.
The ionosphere is the ionized part of the upper atmosphere of the Earth, which plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It influences radio propagation significantly, such as the Global Navigation Satellite System (GNSS). Meanwhile, the GNSS is also an essential technique for sensing the variation of ionosphere. During the years of 2019—2023, a large number of Chinese geodesy scientists devoted much efforts to the geodesy related ionosphere. Due to the very limited length, the achievements are carried out from the following six aspects, including: ① The ionospheric correction models for BDS and BDSBAS; ② Real-time global ionospheric monitoring and modeling; ③ The ionospheric 2D and 3D modeling based on GNSS and LEO satellites; ④ The ionospheric prediction based on artificial intelligence; ⑤ The monitoring and mitigation of ionospheric disturbances for GNSS users; ⑥ The ionospheric related data products and classical applications.
The ocean accounts for approximately 71% of the total area of the Earth. Whether it is studying the shape of the Earth itself through geodesy or the future development of earth system science, strengthening the construction of ocean geodesy disciplines and innovating ocean geodetic observation technologies have evident theoretical and practical significance. In recent years, the discipline of ocean geodesy in China has been continuously developing and growing, and notable breakthroughs have been made in ocean satellite geodesy and seafloor geodetic observation technology. Research on ocean geodetic observation models and algorithms has also made great progress.
Compared with the pair-wise registration of point clouds, multi-view point cloud registration is much less studied. In this dissertation, a disordered multi-view point cloud registration method based on the soft trimmed deep network is proposed. In this method, firstly, the expression ability of feature extraction module is improved and the registration accuracy is increased by enhancing feature extraction network with the point pair feature. Secondly, neighborhood and angle similarities are used to measure the consistency of candidate points to surrounding neighborhoods. By combining distance consistency and high dimensional feature consistency, our network introduces the confidence estimation module of registration, so the point cloud trimmed problem can be converted to candidate for the degree of confidence estimation problem, achieving the pair-wise registration of partially overlapping point clouds. Thirdly, the results from pair-wise registration are fed into the model fusion to achieve the rough registration of multi-view point clouds. Finally, the hierarchical clustering is used to iteratively optimize the clustering center model by gradually increasing the number of clustering categories and performing clustering and registration alternately. This method achieves rough point cloud registration quickly in the early stage, improves the accuracy of multi-view point cloud registration in the later stage, and makes full use of global information to achieve robust and accurate multi-view registration without initial value.
During a long-term Equatorial Plasma Bubbles (EPBs) occurrence between October 2020 and March 2021, a significant EPB suppression event was identified on November 22 and the observations from multi-instrument have been utilized to investigate this event. Global-scale Observations of the Limb and Disk (GOLD) satellite observed prominent EPBs between 23:40 UT and 23:55 UT during the long-term occurrence days. However, no dark stripes representing EPBs were observed on November 22, and the Equatorial Ionization Anomaly (EIA) structure remained intact. The Total Electron Content (TEC) maps show that these EPBs appeared in the region between 35°W and 65°W longitudes and the magnitudes of the TEC loss in EPBs regions were about 20 TECU. Except for 22 November, the S4 index was consistently greater than 0.6 throughout November, indicating significant ionospheric scintillation. The Rate Of TEC Index (ROTI) maps revealed that the spatial extent and intensity of EPBs increased after their suppression, and the EPBs were locally generated. The swarm electron density measurements indicated that the variation amplitudes of EPBs at 510km altitude were approximately 3 to 5 times larger than that at 460km altitude. The impact region of EPBs at 510km was between 15°S and 20°N latitudes, while at 460km, it was between 0° and 17°N latitudes. During the period of EPB suppression, the average h’f at three ionosonde stations decreased by about 50km, and the vertical drift velocity (Vz) approached ~0m/s while it was more than 20 m/s during the long-term occurrence.
The wMPS is a laser-based measurement system used for large scale metrology. However, it is susceptible to external factors such as vibrations, which can lead to unreliable measurements. This paper presents a fault diagnosis and separation method which can counter this problem. To begin with, the paper uses simple models to explain the fault diagnosis and separation methods. These methods are then mathematically derived using statistical analysis and the principles of the wMPS. A comprehensive solution for fault diagnosis and separation is proposed, considering the characteristics of the wMPS. The effectiveness of this solution is verified through experimental observations. It can be concluded that this approach can detect and separate false observations, thereby enhancing the reliability of the wMPS.
《测绘学报(英文版)》(JGGS)由中国科学技术协会主管,中国测绘学会、中国地图出版社有限公司主办,测绘出版社有限公司出版,是《测绘学报》中文版的姊妹刊,面向国内外发行,季刊。