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Precise orbit determination for LEO satellites:single-receiver ambiguity resolution using GREAT products

Geo-Spatial Information Science 2022年第1期25卷 63-73页

作者： Xingxing Li Yujie Qin Keke Zhang Jiaqi Wu Wei Zhang Qian Zhang Hongmin Zhang School of Geodesy and Geomatics Wuhan UniversityWuhanHubeiChina Department of Geodesy and Remote Sensing of the german research centre for geosciences(gfz) PotsdamGermany

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.

关键词： Precise orbit determination single-receiver ambiguity resolution onboard GPS observation LEO

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Comment on 'Will Earth's next supercontinent assemble through the closure of the Pacific Ocean?'

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National Science Review 2022年第12期9卷 70-70页

作者： Bernhard Steinberger centre for Earth Evolution and Dynamics University of Oslo GFZ German Research Centre for Geosciences

In their paper,Huang et al.show that both introversion and extroversion can occur within the same model,if parameters are changed.This by itself is an important result,however,the authors go further to conclude which continents assembled with introversion and which ones with extroversion.This conclusion rests on the assumption that a thicker crust leads to a stronger lithosphere,

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Effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第5期14卷 1461-1469页

作者： Yinlin Ji Christian Kluge Hannes Hofmann Guido Blöcher Helmholtz centre Potsdam GFZ German Research Centre for GeosciencesPotsdam14473Germany State Key Laboratory of Coal Resources and Safe Mining China University of Mining and TechnologyXuzhou221116China

The accurate evaluation of pore pressure and injected volume is crucial for the laboratory characterization of hydromechanical responses of rock fractures. This study reports a series of laboratory experiments to systematically demonstrate the effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture. We characterize the hydraulic aperture of the fracture as a function of effective normal stress using the exponential aperture model.This model is then employed to predict the pore pressure change and injected volume in the fracture without the influences of external temperature and dead volume. The external temperature changes in the cyclic loading test due to the Joule-Thompson effect for fluids. The effect of external temperature on pore pressure change in the fracture can be well explained by thermal pressurization of fluids. Our results also show that the external dead volume can significantly lower the pore pressure change in the fracture during the cyclic loading test under undrained conditions. The injected volume can also be substantially enlarged due to the external dead volume in a typical pore pressure system. Internal measurement of the pore pressure in the fracture using a fiber optic sensor cannot exclude the influences of external temperature and dead volume, primarily because of the good hydraulic communication between the fracture and pore pressure system. This study suggests that the effects of external temperature and dead volume on pore pressure response and injected volume should be evaluated for accurate laboratory characterization and inter-laboratory comparison.

关键词： Fracture aperture Thermal pressurization External dead volume Pressure attenuation Injected volume Fiber optic sensor

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Low-frequency Rayleigh waves excited by the Jan. 15, 2022 eruption of Hunga Tonga-Hunga Ha'apai volcano

Low-frequency Rayleigh waves excited by the Jan. 15, 2022 er...

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2022年中国地球科学联合学术年会

作者： Shenjian ZHANG Rongjiang WANG Xiaofei CHEN Southern University of Science and Technology GFZ German Research Centre for Geosciences Potsdam

After the powerful eruption of Hunga Tonga-Hunga Ha’apai volcano on Jan. 15, 2022, low-frequency signals are detected on long period and very long period seismometers worldwide. The amplitude spectrum of this kind of signals consists of three clear peaks locating at 3.72, 4.61 and 6.07 m Hz. The spectrogram analysis shows that this low-frequency energy lasts for several hour and is independent of air wave arrival, while normal-mode analysis relates this signal to the resonances between the atmosphere and the solid earth.

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Orbit determination and thrust force modeling for a maneuvered GEO satellite using two-way adaptive Kalman filtering

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Science China(Physics,Mechanics & Astronomy) 2012年第4期55卷 738-743页

作者： XU TianHe HE KaiFei XU GuoChang Xi'an research Institute of Surveying and Mapping Xi'an 710054China GFZ German Research Centre for Geosciences Potsdam 14473Germany

A two-way adaptive Kalman filter is proposed by combining a two-way filter with an adaptive filter for orbit determination of a maneuvered GEO satellite.A method of using Newton's high-resolution differential formula and polynomial fitting for modeling the thrust force of a maneuvered GEO satellite is developed.The adaptive factor,which balances the contributions of the measurements and the dynamic model information,is determined by using a two-segment function and predicted residual statistics.Simulations with a maneuvered GEO satellite tracked by the Chinese ground tracking network were conducted to verify the performance of the proposed orbit determination technique and the method of thrust force modeling.The results show that refining the thrust force model is beneficial for the orbit determination of a maneuvered GEO satellite;the two-way adaptive Kalman filter can efficiently control the influence of the dynamic model errors on the orbit state estimate.

关键词：自适应卡尔曼滤波器建模方法推力地球卫星定轨 GEO卫星自适应滤波器操纵

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两种硅酸盐碎屑组分;U/;U测试前处理方法的比较及启示

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矿物岩石地球化学通报 2021年

作者：马松阳李超王晨羽郭玉龙段知非杨守业海洋地质国家重点实验室(同济大学) GFZ German Research Centre for Geosciences Earth Surface Geochemistry

沉积物不同组分（化学相态）的精确提取是还原其所经历地质过程或环境要素的关键。本文比较了两种针对铀系同位素(;U/;U)测试开发的沉积物碎屑组分提取方法,结果表明Francke提出的方法对岩石样品淋洗效果更好。对长江、黄河和台湾浊水... 详细信息

沉积物不同组分（化学相态）的精确提取是还原其所经历地质过程或环境要素的关键。本文比较了两种针对铀系同位素(;U/;U)测试开发的沉积物碎屑组分提取方法,结果表明Francke提出的方法对岩石样品淋洗效果更好。对长江、黄河和台湾浊水溪沉积物样品,Dosseto和Francke建议的方法各有优势。此外,本文还发现台湾浊水溪流域岩石露头样品的(;U/;U)并没有如预期处于久期平衡状态,可能是因为岩石样品混入了部分次生物质,也可能与该岩石露头样品多为砂岩、孔隙较发育而产生了明显的优先淋滤有关。本研究对于表生环境下沉积物硅酸盐碎屑组分(;U/;U)的精确测定具有一定的参考价值,同时对于岩石铀系不平衡研究也有一定启示意义。

关键词：碎屑组分提取顺序淋滤 ( U/ U) 岩石沉积物

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Revisiting the dissolution of biogenic Si in marine sediments： a key term in the ocean Si budget

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Acta Geochimica 2017年第3期36卷 429-432页

作者： Patrick Frings Department of Geoscience Swedish Museum of Natural History 10405 Stockholm Sweden Earth Surface Geochemistry GFZ German Research Centre for Geosciences 14473 Telegrafenberg Potsdam Germany

Of the　~240*10^(12)mol year^(-1)of biogenic silica(bSi)produced by diatoms and other silicifying organisms,only roughly 3%–4%escapes dissolution to be permanently buried.At the global scale,how,where and why b Si is preserved in sediment is not well understood.To help address this,I compile 6245 porewater dissolved Si concentrations from 453 sediment cores,to derive the concentration gradient at the sediment–water interface and thus diffusive fluxes out of the sediment.These range from\0.002 to 3.4 mol m^(-2)year^(-1),and are independent of temperature,depth and latitude.When classified by sediment lithology,predominantly siliceous sediments unsurprisingly have higher mean diffusive fluxes than predominantly calcareous or clay-rich sediment.Combined with the areal extent of these lithologies,the‘best-guess’global sedimentary b Si recycling flux is69 9 10^(12)mol year^(-1).

关键词：海洋沉积物生物硅溶解硅术语预算浓度梯度扩散通量岩性分类

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Mutual impact of true triaxial stress, borehole orientation and bedding inclination on laboratory hydraulic fracturing of Lushan shale

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第12期15卷 3131-3147页

作者： Yongfa Zhang Anfa Long Yu Zhao Arno Zang Chaolin Wang College of Civil Engineering Guizhou UniversityGuiyang550025China Helmholtz centre Potsdam GFZ German Research Centre for GeosciencesPotsdam14473Germany

Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.

关键词： True triaxial hydraulic fracturing experiment In situ stress state Bedding planes Natural fractures Wellbore orientation Shale reservoirs

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Automatic inversions of strong-motion records for finite-fault ruptures of earthquakes in Japan

Automatic inversions of strong-motion records for finite-fau...

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2019年中国地球科学联合学术年会

作者： Xujun Zheng Yong Zhang Rongjiang Wang School of Earth and Space Sciences Peking University Helmholtz centre Potsdam GFZ German Research Centre for Geosciences

Automatic and rapid imaging of earthquake rupture process is a difficult task but critical for post-earthquake response and possible tsunami early warnings. We develop an automatic system for the i

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Simulation of Pre-P-wave elasto-gravitational signals of 2011 Tohoku Mw9.1 Earthquake

Simulation of Pre-P-wave elasto-gravitational signals of 201...

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2019年中国地球科学联合学术年会

作者： Shenjian Zhang Rongjiang Wang Torsten Dahm Shiyong Zhou Sebastian Heimann School of Earth and Space Sciences Peking University Helmholtz centre Potsdam GFZ German Research Centre for Geosciences

An earthquake causes a sudden rock-mass redistribution through fault rupture and generates seismic waves that can result in bulk density variations propagating with them. Both processes induce gravity perturbations in the earth, signals of which propagate with the speed of light and therefore can arrive at remote stations earlier than the fastest P

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