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  • 1
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    River-Dominated Shelf Sediments of East Asian Seas (2016)
    London : The Geological Society
    Details
    Description / Table of Contents: The rivers of East Asia are some of the largest and most important to human society and the global economy. They drain a variety of terrains from the Tibetan plateau, the hill country of southern China and the steep mountains of Taiwan. The sediment they carry potentially records the long-term evolution of continental environments within the marine stratigraphic record. Sediments reaching the ocean have to traverse the wide continental shelves where they may be reworked and transported by longshore currents, typhoon storm waves, as well as large ocean currents such as the Kuroshio. Deciphering any marine record requires us to understand the dynamics of sediment transport on the continental shelves, and this region acts as a global type example of such processes. Studies in this volume span a wide range of subdisciplines in the marine sciences and provide new insights into how sediment is distributed offshore after leaving the river mouths.
    Pages: Online-Ressource (VI, 268 Seiten)
    ISBN: 9781862397408
    URL: http://sp.lyellcollection.org/content/429/1
    Language: English
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  • 2
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    Galileo and QZSS precise orbit and clock determination using new satellite metadata (2019)
    In:  Journal of Geodesy
    Details
    Publication Date: 2020-02-12
    Description: During 2016–2018, satellite metadata/information including antenna parameters, attitude laws and physical characteristics such as mass, dimensions and optical properties were released for Galileo and QZSS (except for the QZS-1 optical coefficients). These metadata are critical for improving the accuracy of precise orbit and clock determination. In this contribution, we evaluate the benefits of these new metadata to orbit and clock in three aspects: the phase center offsets and variations (PCO and PCV), the yaw-attitude model and solar radiation pressure (SRP) model. The updating of Galileo PCO and PCV corrections, from the values estimated by Deutsches Zentrum für Luft- und Raumfahrt and Deutsches GeoForschungsZentrum to the chamber calibrations disclosed by new metadata, has only a slight influence on Galileo orbits, with overlap differences within only 1 mm. By modeling the yaw attitude of Galileo satellites and QZS-2 spacecraft (SVN J002) according to new published attitude laws, the residuals of ionosphere-free carrier-phase combinations can be obviously decreased in yaw maneuver seasons. With the new attitude models, the 3D overlap RMS in eclipse seasons can be decreased from 12.3 cm, 14.7 cm, 16.8 cm and 34.7 cm to 11.7 cm, 13.4 cm, 15.8 cm and 32.9 cm for Galileo In-Orbit Validation (IOV), Full Operational Capability (FOC), FOC in elliptical orbits (FOCe) and QZS-2 satellites, respectively. By applying the a priori box-wing SRP model with new satellite dimensions and optical coefficients, the 3D overlap RMS are 5.3 cm, 6.2 cm, 5.3 cm and 16.6 cm for Galileo IOV, FOCe, FOC and QZS-2 satellites, with improvements of 11.0%, 14.7%, 14.0% and 13.8% when compared with the updated Extended CODE Orbit Model (ECOM2). The satellite laser ranging (SLR) validation reveals that the a priori box-wing model has smaller mean biases of − 0.4 cm, − 0.4 cm and 0.6 cm for Galileo FOCe, FOC and QZS-2 satellites, while a slightly larger mean bias of − 1.0 cm is observed for Galileo IOV satellites. Moreover, the SLR residual dependencies of Galileo IOV and FOC satellites on the elongation angle almost vanish when the a priori box-wing SRP model is applied. As for satellite clocks, a visible bump appears in the Modified Allan deviation at integration time of 20,000 s for Galileo Passive Hydrogen Maser with ECOM2, while it almost vanishes when the a priori box-wing SRP model and new metadata are applied. The standard deviations of clock overlap can also be significantly reduced by using new metadata.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 3
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    ESA Field-Aligned Currents—Methodology Inter-comparison Exercise (2020)
    In:  Ionospheric Multi-Spacecraft Analysis Tools | ISSI Scientific Report Series
    Details
    Publication Date: 2020-05-09
    Description: Various ESA projects and several proposals to first Swarm DISC Call for Ideas (May 2016) suggested possible evolution for the current Swarm Level 2 FAC products, and the implementation of quality flags for the FAC products. The Field-Aligned Currents—Methodology Inter-Comparison Exercise (FAC-MICE) consisted in comparison of the various methods to determine the FAC from Swarm data, with a test dataset of 28 Swarm auroral crossings delivered to participants last June. Eight groups performed the FAC-MICE analysis. The results of this exercise, discussed in the dedicated ‘Swarm Ionospheric Currents Products workshop’ in ESTEC on September 2017, highlighted the strengths of the various methods/approaches. Following discussion with the participants to this workshop, we are now working to develop an open source platform for user-definable FAC calculation.
    Language: English
    Type: info:eu-repo/semantics/bookPart
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  • 4
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    Efficient permeability prediction of digital porous media via classical machine learning models and deep learning model LSTM (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-03
    Description: Pore-scale numerical simulation plays an important role in comprehending water quality. Predicting the permeability of porous media via machine learning models is a crucial aspect of current research in pore-scale modelling. These models can create a mapping relationship between permeability and pore structure, serving as a regression task. However, directly applying 3D data of porous media to classical machine learning models is not possible, requiring the extraction of features from the pore structure. Deep learning models, as an advanced form of classical machine learning, have been successful in permeability prediction using 3D digital images, but come at a high computational cost. To address this, we propose an intuitive feature extraction method that extracts pore structure features from slices of 3D porous media and uses them as input for machine learning models. This not only reduces the amount of input data but also improves training efficiency, while maintaining excellent prediction accuracy. Moreover, due to the spatial continuity of the 2D pore structure features, we achieved improved prediction performance compared to classical machine learning models by using a long short-term memory (LSTM) neural network. The use of transfer learning further demonstrates the LSTM model's remarkable generalization ability.
    Language: English
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  • 5
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    Spatiotemporal deformation analysis of 2021 Maduo Mw7.4 earthquake in China by using Sentinel-1 SAR images (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-15
    Description: On May 22, 2021, an Mw7.4 earthquake occurred in Maduo, Qinghai, China. The epicenter was located at 34.59 degrees north latitude and 98.34 degrees east longitude. This paper uses ASF HyP3 and MintPy software to conduct time-series InSAR analysis by using the Sentinel-1 SAR images from 2018 to 2023, and then to study the temporal and spatial distribution of regional crustal deformation and the distribution of the seismic fault ruptures. The time-series InSAR analysis are taken in three groups: Pre-earthquake period from January 2018 to May 2021, Earthquake onset period from April 2021 to June 2021, and Post-earthquake period From June 2021 to January 2023. The LOS(Light of Sight) velocity results of the time series INSAR analysis in the three groups and three dimension velocity of GPS stations in this area are fused to obtain regional tectonic strain rates, co-seismic fault slips, and post-seismic displacements. The results show that crustal deformation before the earthquake is small, the range of the coseismic surface rupture of the Maduo earthquake overlaps with the abnormal area of the regional strain field obtained, and the post-seismic viscoelastic deformation is strongly correlated with Maduo earthquake fault.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 6
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    Boosting effect of the strong west pole of the Indian Ocean Dipole on the decay of El Niño (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-08
    Description: Although the impact of the Indian Ocean on the decaying pace of El Niño events has been documented previously, contrary to the consensus that the Indian Ocean Basin (IOB) mode favors the decay of El Niño via modulating the zonal wind anomalies in the tropical western Pacific, the contribution of the Indian Ocean Dipole (IOD) on the following year’s El Niño remains highly controversial. Through investigating the evolution of fast and slow decaying El Niño events, this study demonstrates that the positive IOD phase with a strong western pole prompts the termination of El Niño, whereas no significant effect of the IOD with a weak western pole. The responsible physical mechanism is that the strong western pole of a positive IOD can lead to a strong IOB pattern along with peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising (sinking) motions over the tropical Indian Ocean (western Pacific Ocean). The surface easterly wind anomalies on the western flank of the sinking motions stimulate oceanic upwelling equatorial Kelvin waves, which shoal the thermocline in the equatorial eastern Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of IOD induces a weak IOB mode that peaks in late spring, and the above cross-basin physical processes will not appear.
    Language: English
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  • 7
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    LEO-based geocenter motion estimation using dynamic force models and onboard GNSS observations (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-06-29
    Description: Low earth orbit (LEO) satellites have a natural advantage in sensing geocenter motion due to their low altitude. However, the complicated low-altitude space environment poses notable challenges for LEO orbit modeling, which can eventually impact the quality of derived geocenter motion. In this study, we focus on the LEO-based geocenter estimation. The geocenter motion is directly estimated in the LEO dynamic POD without incorporating ground GNSS observations. We use dynamic models instead of onboard accelerometer measurements for the non-gravitational forces in order to investigate the impact of orbit modeling on the geocenter estimation. Three year (2019-2021) onboard GNSS observations from seven LEO satellites in different orbits are processed. Our results indicate a strong correlation between LEO solar radiation pressure (SRP) modeling and estimated geocenter motion. The imperfections of a priori box-wing model can result in severe distortions of geocenter estimates, especially for the Z components. But by introducing a SRP scale factor, most orbital artifacts signal in the geocenter coordinates can be eliminated, and the time resolution of SRP scale factor have a negligible influence on the geocenter estimates. Furthermore, we compare our result with the solution based on the accelerometer measurements, and observed a good consistency in the annual signal characteristic of both solutions. We also evaluate the contribution of multiple LEO combination to the geocenter estimation. The combination of multiple LEO can significantly reduce the corelation between geocenter coordinates and orbit dynamic parameters, thereby improving the reliability of the derived geocenter motion.
    Language: English
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  • 8
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    Slant range measurements of the corner reflector by using SAR imaging geodesy (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-07-19
    Description: In this paper, a point target analysis method is developed for measuring the slant range from SAR satellite to the ground corner reflector. By using the pre-measured coordinate of the corner reflector and the precise orbit of SAR satellite, the theoretical slant range can be calculated, and the residual of the corrected slant range measurement by point target analysis is then obtained. For repeated SAR images over corner reflectors, the time series of the residual of measured slant ranges can be formed and used to detect displacements of corner reflectors. This method has been used to analyze five corner reflectors in Shanghai by using tens of Sentinel-1A SAR images. All the five corner reflectors are in same shape and size, which is triangular trihedral with inner-leg of 1.2 meter. Two of the five corner reflectors are located on stable ground, and three of them are located on Shanghai Yangtze River Bridge. The results show that the average standard deviation of the residual is about 0.15m, and it is affected by the nearby scattering environment of the individual corner reflector. The vibration of the bridge leads to larger standard deviations of the residuals. In addition, re-setup experiments of the two ground corner reflectors are conducted, they are raised up by 0.10m intentionally, which can be detected successfully through analysis of the residual time series. This method can be used to monitor large displacement of ground movements, such as landslides and movements of mining dams, by using high resolution SAR images.
    Language: English
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  • 9
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    Thermal lithospheric thickness and bottom boundary morphology of the North China Craton after thermal subsidence (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-05-16
    Description: The present day’s thermal lithospheric thickness is usually calculated by one or two-dimensional steady-state heat conduction equation. Using the latest measured heat flow data of the North China Craton(NCC) and the one-dimensional steady-state heat conduction equation, the calculated thermal lithospheric thickness of the NCC is between 34.8-190 km. There are some regions, whose lithosphere is very thin, and the lithosphere adjacent to them is very thick, so the bottom boundary of the lithosphere fluctuates greatly. The last thinning of the NCC stopped at~24 Ma and then entered the thermal subsidence period. To study whether the fluctuates of the bottom boundary of the lithosphere can be maintained during the long-term thermal subsidence process, a thermal subsidence model was established. The modeling results show that after the thermal subsidence of 24 Ma, the fluctuates of the bottom boundary of the lithosphere are difficult to maintain, and the present day’s thermal lithospheric thickness of the NCC should not exceed 73 km, and the maximum surface heat flow value of the NCC is 75.6 mW·m〈sup〉-2〈/sup〉 due to the deep thermal state. The high heat flows anomaly in the NCC is more caused by shallow activities and cannot reflect the deep thermal state. After correction, the current thermal lithospheric thickness of the North China craton is ~73-190 km, and the bottom boundary of the lithosphere changes gently.
    Language: English
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  • 10
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    Precise orbit determination for LEO satellites: single-receiver ambiguity resolution using GREAT products (2022)
    In:  Geo-Spatial Information Science
    Details
    Publication Date: 2023-02-01
    Description: In recent years, the large Low Earth Orbit (LEO) constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems (GNSS) positioning performance. One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites. The GNSS-based Precise Orbit Determination (POD) will be exclusively performed to achieve this goal, where the Integer Ambiguity Resolution (IAR) plays a key role in acquiring high-quality orbits. In this study, we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations. We perform ambiguity-fixed LEO POD for four typical missions, including Gravity Recovery and Climate Experiment (GRACE) Follow-On (GRACE-FO), Swarm, Jason-3 and Sentinel-3, using the Uncalibrated Phase Delay (UPD) products generated by our GREAT (GNSS+ REsearch, Application and Teaching) software. The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits. There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias (OSB) and Integer Recovery Clock (IRC) products, indicating the good-quality of UPD products we generated. Compared to the float solution, the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites. Meanwhile, the benefit can be observed in laser ranging residuals as well, with a Standard Deviation (STD) reduction of 3–4 mm on average for the fixed solutions. Apart from the absolute orbits, the relative accuracy of the space baseline is also improved by 20–30% in the fixed solutions. The result demonstrates the superior performance of the ambiguity-fixed LEO POD, which appears as a particularly promising technique for POD of future LEO constellations.
    Language: English
    Type: info:eu-repo/semantics/article
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