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LEO satellite clock analysis and prediction for positioning applications

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Geo-Spatial Information Science 2022年第1期25卷 14-33页

作者： Kan Wang Ahmed El-Mowafy school of earth and Planetary sciences Curtin UniversityPerthAustralia

The positioning service aided by low earth orbit(LEO)mega-constellations has become a hot topic in recent years.To achieve precise positioning,accuracy of the LEO clocks is important for single-receiver users.To bridge the gap between the applicable time of the clock products and the time of positioning,the precise LEO clocks need to be predicted over a certain period depending on the sampling interval of the clock products.This study discusses the prediction errors for periods from 10 s to 1 h for two typical LEO clock types,i.***.the ultra-stable oscillator(USO)and the oven-controlled crystal oscillator(OCXO).The prediction is based on GNSS-determined precise clock estimates,where the clock stability is related to the GNSS estimation errors,the behaviors of the oscillators themselves,the systematic effects related to the environment and the relativistic effects,and the stability of the time reference.Based on real data analysis,LEO clocks of the two different types are simulated under different conditions,and a prediction model considering the systematic effects is proposed.Compared to a simple polynomial fitting model usually applied,the proposed model can significantly reduce the prediction errors,i.***.by about 40%-70%in simulations and about 5%-30%for real data containing different miss-modeled effects.For both clock types,short-term prediction of 1 min would result in a root mean square error(RMSE)of a few centimeters when using a very stable time reference.The RMSE amounts to about 0.1 m,when a typical real-time time reference of the national center for space studies(CNES)real-time clocks was used.For long-term prediction of 1 h,the RMSE could range from below 1 m to a few meters for the USOs,depending on the complexity of the miss-modeled effects.For OCXOs,the 1 h prediction could lead to larger errors with an RMSE of about 10 m.

关键词： LEO clock prediction USO OCXO relativistic effects

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华北克拉通冀东地体超高温麻粒岩的新发现

Science Bulletin 2022年第7期67卷 670-673页

作者：刘婷魏春景 Tim E.Johnson Elena Sizova College of earth sciences Chengdu University of TechnologyChengdu 610059China school of earth and Space sciences Peking UniversityBeijing 100871China school of earth and Planetary sciences the Institute for Geoscience ResearchCurtin UniversityPerthWA 6845Australia Institute of earth sciences University of GrazGraz 8010Austria

Archean crustal terranes are commonly featured with the dome–and–keel structures,in which supracrustal rocks occur as belts(greenstones)between,and rafts within,dome-like bodies of tonalite–trondhjemite–granodiorite(TTG).Supracrustal rafts within TTG gneisses generally record metamorphic grades ranging from amphibolite-to ultra-high temperature(UHT)granulitefacies of low-to moderate-pressure conditions[1].Notably,granulite-facies rafts commonly show counterclockwise P±T paths involving a significant increase in pressure at high temperatures[2,3].However,the tectonothermal drivers behind such metamorphism are still debated.

关键词： crustal 超高温麻粒岩 facies

Latitudinal and Seasonal Variations in Tropical Cyclone-Induced Ocean Surface Cooling in the Tropical Western North Pacific

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Journal of Meteorological Research 2023年第6期37卷 790-801页

作者： Mengxi JIN Ziyuan ZHAO Renguang WU Peijun ZHU School of Earth Sciences Zhejiang UniversityHangzhou310058China

The passage of tropical cyclones induces ocean surface cooling through vertical mixing,upwelling,and surface heat loss.The dependence of tropical cyclone-induced ocean surface cooling on the intensity and translation speed of tropical cyclones has been documented in previous studies.The present study investigates the latitudinal and seasonal variations in tropical cyclone-induced ocean surface cooling in the tropical western North Pacific based on data for the 2001–2020 period.Our analysis focuses on the open ocean(0°–25°N,130°E–180°)to reduce the interference of coastal topography so that the obtained results better represent the influences of the intensity and translation speed of tropical cyclones.Our analysis confirms the dependence on the intensity and translation speed of tropical cyclone-induced cooling.The new findings are as follows.First,the time to reach the maximum cooling increases with the magnitude of the maximum cooling.Second,the magnitude of ocean surface cooling increases with latitude in the tropical region for tropical cyclones with different intensities and translation speeds.Third,the ocean surface cooling is larger in summer and autumn than in spring for tropical cyclones with different intensities and translation speeds.Fourth,the dependence of ocean surface cooling on the translation speed is more obvious at higher latitudes in the tropics and less apparent in spring.These new findings add to the existing knowledge of the impacts of tropical cyclone intensity and translation speed on ocean surface cooling.

关键词： tropical cyclones ocean surface cooling intensity and translation speed latitudinal dependence seasonal variation

A cross-type imaging electron spectrometer

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Science China(Technological sciences) 2023年第3期66卷 641-653页

作者： YE YuGuang ZOU Hong WANG YongFu QIN JunFeng SHI WeiHong ZOU JiQing ZHONG WeiYing ZONG QiuGang FU SuiYan school of earth and Space sciences Peking UniversityBeijing 100871China

Energetic electron measurement is of great significance to theoretical space physics research and space weather applications.Current energetic electron detectors must cooperate with a spin-stabilized satellite platform to achieve high angular resolution in pitch angle distribution and three-dimensional(3D)imaging measurement of energetic electrons.This article introduces a cross-type quasi-3D imaging electron spectrometer(IES)based on pinhole imaging technology developed in the laboratory.The imager is composed of five imaging units,including a nine-pixel area array Si-PIN detector imaging unit in the middle and four three-pixel linear array Si-PIN detector imaging units placed in a cross-shape around it.The combination of five imaging units forms two orthogonal nine-pixel linear array detectors(with a common pixel in the middle).There are four pixels with a view angle of 20°×20°in the 45°oblique directions of the cross-type detection array.There are 21 imaging pixels in the entire crosstype sensor head,corresponding to 21 directions.Two multichannel integrated preamplifier ASICs are integrated in the sensor head to realize particle signal readout from 21 pixels.With a back-end electronics system,each pixel can achieve high energy resolution detection of 50–600 keV electrons.Radioactive sources and electron accelerators are used to calibrate the cross-type imaging sensor head,and the results demonstrate its good energy and directional detection characteristics(the energy resolution reaches 6.9 keV for the incident 200 keV electron beam).We performed simulations on the imaging sensor head’s ability to measure the electron pitch angle distribution on the three-axis stabilized platform,and the results show that the sensor head can perform quasi-three-dimensional detection of electrons incident within 2πsolid angles on the three-axis stabilized satellite platform,with an average angular resolution of the electron pitch angle distribution of less than 6°.

关键词： energetic electron detection imaging electron spectrometer cross-type sensor head pitch angle distribution

Provenance of the Lower Jurassic pyroclastic sediments in the Zigui Basin:Implication for crustal thickening in the eastern Qinling orogenic belt

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Science China earth sciences 2024年第1期67卷 196-207页

作者： Rong CHAI Jianghai YANG Yuansheng DU Chengshan WANG School of Earth Sciences and Resources China University of Geosciences(Beijing)Beijing 100023China School of Earth Sciences China University of Geosciences(Wuhan)Wuhan 430074China Chinese Academy of Geological sciences Beijing 100037China

The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt,accompanied by magma underplating and tectonic deformation.These processes potentially resulted in substantial crustal thickening and uplift of the Qinling orogen.However,due to the absence of igneous rock records from this period in the eastern section of the Qinling orogen,the changes in crustal thickness during this orogenic process have not been thoroughly investigated.A series of foreland basins emerged during the Early Mesozoic to the south of the East Qinling orogenic belt.These basins have preserved clastic sedimentary rocks derived from the uplift and erosion of the orogenic belt.These sedimentary records serve as crucial records to reconstruct the evolutionary history of the Qinling orogen.To further clarify the collisional orogenic process of the Qinling orogenic belt,this study conducted in situ volcanic lithic fragment geochemistry,detrital zircon U-Pb chronology and trace element composition analysis on the sandstones of the Lower Jurassic Tongzhuyuan Formation in the Zigui Basin.The results suggest that the sandstones,which exhibit a significant abundance of volcanic lithic fragments,has a characteristic detrital zircon age group of 250–200 Ma,indicating a major provenance from the Triassic volcanic rocks.Combined with regional correlation and paleocurrent analysis,the detrital zircon U-Pb age data show that the source area of volcanic rocks should be in the Qinling orogenic belt to the north of the basin.This interpretation is further supported by the Triassic granitic rocks exposed in the western part of the orogenic belt,representing the magmatism during the Triassic collisional orogenesis in the Qinling orogen.Based on the co-varying relationships between present-day crust thickness with the chemical compositions of granite rocks and zircons,the La/Yb ratio of volcanic lithic fragments in the Tongzhuyuan Formation and the Eu/Eu*ratio of detrital zircons with Triassic ages indicate that the Qinling o

关键词： Qinling orogenic belt Zigui Basin Late Triassic Detrital zircons Crustal thickening

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为什么地球上超大陆的寿命变得越来越短了?

Science Bulletin 2023年第4期68卷 436-440,M0004页

作者：黄川李正祥 earth Dynamics Research Group the Institute for Geoscience ResearchSchool of Earth and Planetary SciencesCurtin UniversityPerth WA 6845Australia

地球上的主要大陆地块在过去的20亿年间以来曾经三次聚合成一个超大陆,但一段时间以后又发生裂解.这种大陆地块的周期性聚合和裂解现象被称为超大陆旋回.地球通过超大陆旋回控制着地表的造山运动、成矿过程、大洋及超大洋的形成与闭合,... 详细信息

地球上的主要大陆地块在过去的20亿年间以来曾经三次聚合成一个超大陆,但一段时间以后又发生裂解.这种大陆地块的周期性聚合和裂解现象被称为超大陆旋回.地球通过超大陆旋回控制着地表的造山运动、成矿过程、大洋及超大洋的形成与闭合,甚至大气圈与生命圈的演化.但一个有趣的观察是,已知的由老到新的努纳(也称哥伦比亚)、罗迪尼亚(最早音译鲁迪尼亚)和盘古三个超大陆的寿命显示出一个逐渐递减的趋势,其分别为大约3亿年,2~2.5亿年和1.5亿年,反映出控制地球长期演化过程的某种重要的内在原因.本文通过超级电脑地球动力学三维建模发现,导致超大陆寿命不断减短的主要原因在于形成于超大陆内部的新的造山带的强度随着地球的年龄增大而逐渐减小,并进而提出这与地球的长期冷却过程有关.因为地幔温度随着地球年龄的增长在不断降低,上地幔岩石部分熔融的程度也在不断降低,因此造成新生造山带的岩石圈厚度不断减薄,强度降低.此外,沿新生造山带的岩浆底侵对板块缝合线及大断裂的岩浆缝合作用可能也会随之减弱.

关键词： Supercontinental lifespan Youngorogens Yieldstress Secularcooling

Hybrid absorbing boundary condition based on transmitting boundary and its application in 3D fractional viscoacoustic modeling

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Petroleum Science 2023年第2期20卷 840-856页

作者： Song-Ling Li Ying Shi Ning Wang Wei-Hong Wang Xuan Ke School of Earth Sciences Northeast Petroleum UniversityDaqingHeilongjiang 163318China

An accurate numerical simulation for wave equations is essential for understanding of wave propagation in the earth's interior as well as full waveform inversion and reverse time migration. However, due to computational cost and hardware capability limitations, numerical simulations are often performed within a finite domain. Thus, an adequate absorbing boundary condition (ABC) is indispensable for obtaining accurate numerical simulation results. In this study, we develop a hybrid ABC based on a transmitting boundary, which is referred to as THABC, to eliminate artificial boundary reflections in 3D second-order fractional viscoacoustic numerical simulations. Furthermore, we propose an adaptive weighted coefficient to reconcile the transmitting and viscoacoustic wavefields in THABC. Through several numerical examples, we determine that the proposed THABC approach is characterized by the following benefits. First, with the same number of absorbing layers, THABC exhibits a better ability in eliminating boundary reflection than traditional ABC schemes. Second, THABC is more effective in computation, since it only requires the wavefields at the current and last time steps to solve the transmitting formula within the absorbing layers. Benefiting from a simple but effective combination between the transmitting equation and the second-order wave equation, our scheme performs well in the 3D fractional Laplacian viscoacoustic numerical simulation.

关键词： Hybrid absorbing boundary Numerical simulation Transmitting boundary Fractional viscoacoustic wave equation

Evolution of the deformation field and earthquake fracture precursors of strike-slip faults

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earth and Planetary Physics 2020年第2期4卷 151-162页

作者： Qi Zhang YongHong Zhao Hang Wang Muhammad Irfan Ehsan JiaYing Yang Gang Tian ANDong Xu Ru Liu YanJun Xiao school of earth and Space sciences Peking University

Seismic hazard analysis is gaining increased attention in the present era because of the catastrophic effects of earthquakes.Scientists always have as a goal to develop new techniques that will help forecast earthquakes before their reoccurrence. In this research,we have performed a shear failure experiment on rock samples with prefabricated cracks to simulate the process of plate movement that forms strike-slip faults. We studied the evolution law of the deformation field to simulate the shear failure experiment, and these results gave us a comprehensive understanding of the elaborate strain distribution law and its formation process with which to identify actual fault zones. We performed uniaxial compression tests on marble slabs with prefabricated double shear cracks to study the distribution and evolution of the deformation field during shear failure. Analysis of the strain field at different loading stages showed that with an increase in the load, the shear strain field initially changed to a disordered-style distribution. Further, the strain field was partially concentrated and finally completely concentrated near the crack and then distributed in the shape of a strip along the crack. We also computed coefficients of variation(CVs) for the physical quantities u, v, and exy, which varied with the load. The CV curves were found to correspond to the different loading stages. We found that at the uniform deformation stage, the CV value was small and changed slowly,whereas at the later nonuniform deformation stage, the CV value increased sharply and changed abruptly. Therefore, the precursor to a rock sample breakdown can be predicted by observing the variation characteristics of CV statistics. The correlation we found between our experimental and theoretical results revealed that our crack evolution and sample deformation results showed good coupling with seismic distribution characteristics near the San Andreas Fault.

关键词： strike-slip fracture digital image correlation method evolution of deformation field rock failure fracture precursor

Strain Geometry and Vorticity Analysis of the Deformed Radiolarian Rocks in the Abade-Tashk Area,the Zagros Suture Zone,Iran

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Journal of earth Science 2022年第2期33卷 525-540页

作者： Roghyeh Tavakkoli Khalil Sarkarinejad Saeede Keshavarz Seyed Rahim Hosseini Department of earth sciences School of ScienceShiraz UniversityShiraz ***Iran Department of earth sciences Graduate University of Advanced TechnologyKerman ***Iran

Deformation in the Zagros suture zone is a result of the oblique collision of the AfroArabian continent with the Central Iranian microcontinents.Various types of folding and faulting are characteristic features of the study area and indicate the performance of a high strain tectonic regime in this region.To distinguish deformation geometry during the collisional events,strain measurements have been carried out,using the R_(f)/φ method on deformed radiolarian microfossils,in the Zagros suture zone.Based on the results,the strain ellipsoid shape is in the range of general flattening to plane strain(K=0.16 – 1.12).Measured mean kinematic vorticity number(W_(m)) in the deformed radiolarian rocks ranges between 0.50 and 0.87,which implies that exhumation of the Abade-Tashk area was facilitated by a general shear flow(35%

关键词： transpression Zagros suture zone deformed radiolarian microfossils vorticity analysis Abade-Tashk area tectonicstranspression Zagros suture zone deformed radiolarian microfossils vorticity analysis Abade-Tashk area tectonics