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ETH-GQS: An estimation of geoid-to-quasigeoid separation over Ethiopia

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geodesy and geodynamics 2022年第1期13卷 31-37页

作者： Ephrem Y.Belay Walyeldeen Godah Malgorzata Szelachowska Robert Tenzer Ethiopian Space Science and Technology Institute Addis Ababa Ethiopia centre of geodesy and geodynamics Institute of Geodesy and Cartography(IGiK)WarsawPoland Department of Land Surveying and Geo-Informatics Hong Kong Polytechnic UniversityHong KongChina

The determination of accurate orthometric or normal heights remains one of the main challenges for the geodetic community in *** heights are required for geodetic and geodynamic scientific research as well as for extensive engineering *** main objective of this study is to estimate the geoid-to-quasi geoid separation(GQS)in Ethiopia(ETH-GQS).Such separation would be required for the conversion between geoid and quasigeoid models,which is mandatory for the determination of accurate geodetic heights in mountain *** airborne free-air gravity anomalies and the topo-graphic information retrieved from the SRTM3(Shuttle Radar Topography Mission of a spatial resolution 3 arc-second)digital elevation model were used to compute the ETH-GQS model according to the Sjoberg's strict formula for the geoid-to-quasigeoid *** ETH-GQS was then validated using GNSS-levelling data as well as geoid heights determined from different Global Geopotential Models(GGMs),namely the EGM2008,EIGEN-6C4 and *** results reveal that the standard deviation of differences between the geoid heights obtained from the EIGEN-6C4 model and the geometric geoid heights obtained from GNSS-levelling data were improved by~75%(***~24 to~6 cm)when considering GQS values obtained from the ETH-GQS.

关键词： Geoid-to-quasigeoid separation GNSS-Levelling Ethiopian vertical control network Orthometric and normal heights Airborne gravity data

Regional TEC modelling over Africa using deep structured supervised neural network

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geodesy and geodynamics 2020年第5期11卷 367-375页

作者： Mefe Moses Joseph Danasabe Dodo Lazarus Mustapha Ojigi Kola Lawal Department of Geomatics Ahmadu Bello UniversityZariaKadunaNigeria centre for geodesy and geodynamics NASRDAToroBauchi StateNigeria

A deep structured supervised neural network(NN) model has been developed for modelling of ionospheric vertical total electron content(VTEC) using observations from over 100 Global Navigation Satellite System continuously operating reference stations(GNSS CORS) across Africa. The study covers all available data during low, moderate and declining phases of solar cycle 24, from 2009 to 2017. Optimal network parameters combination for the regional model includes a combination of spatio-temporal parameters(latitude, longitude, year, day of the year, hour), geomagnetic and solar parameters(F10.7, AE,Dst indices), hidden layer of 20 neurons and a feedforward network with Levenberge Marquardt backpropagation algorithm. The validation and the test curves do not indicate overfitting and the performance curves of the training, validation and test data show a very similar trend. Thus, the performance of the optimal network with learning data is in sync with the data not assimilated in the learning *** African Regional Ionospheric Tec Model(ARITM) developed in this study reproduces the known spatiotemporal features of the equatorial and low-latitudes ionosphere quite well. The ARITM performs well to a considerably high degree of precision within the Africa region by comparison with the global ionospheric maps(GIMs) and the Formosa Satellite-3 Constellation Observing System for Meteorology,Ionosphere & Climate(FORMOSAT-3/COSMIC) observations. The results suggest that the developed model can efficiently be adopted as a substitute for single station ionospheric model for any single GNSS station within Africa, avoiding the need for developing independent multiple single station ionospheric models for each of the existing and future GNSS stations within the African region.

关键词： latitude Regional equatorial

Consistency analysis of GRACE and GRACE-FO data in the study of global mean sea level change

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geodesy and geodynamics 2022年第4期13卷 321-326页

作者： Le Chang Wenke Sun College of geodesy and Geomatics Shandong University of Science and TechnologyQingdao266590China Key Laboratory of Computational geodynamics University of Chinese Academy of SciencesBeijing100049China

Global mean sea level(GMSL) change is one of the important indicators of global climate change and is a crucial scientific issue of continuing interest. As satellite altimeter data, the Gravity Recovery and Climate Experiment(GRACE) and Argo continue to be updated, especially with the release of GRACE Follow-On(GRACE-FO) data, making it necessary to combine these latest data to estimate sea level change. Determinations on whether the GRACE and GRACE-FO observation systems provide unbiased global observation data have not been effectively evaluated. Therefore, this research mainly investigated the consistency of GRACE and GRACE-FO observation data in studying GMSL change. By comparing the sum of the GMSL calculated by the two gravity satellites and Argo data with the GMSL calculated by satellite altimeters, the discrepancy between GRACE-FO + Argo and satellite altimeter data is about 7.9 ± 2.3 mm, which is likely derived from the inconsistency between GRACE and GRACE-FO data.

关键词： GMSL GRACE GRACE-FO Altimetry Argo

Constraining Shear Wave Velocity and Density Contrast at the Inner Core Boundary with PKiKP/P Amplitude Ratio

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Journal of Earth Science 2013年第5期24卷 716-724页

作者：曾祥方倪四道 CAS Key Laboratory of Computational geodynamics University of Chinese Academy of Sciences Mengcheng National Geophysical Observatory University of Science and Technology of China State Key Laboratory of geodesy and Earth’s Dynamics Institute of Geodesy and GeophysicsChinese Academy of Sciences

Shear velocity and density contrast across the inner core boundary are essential for stud- ying deep earth dynamics, geodynamo and geomagnetic evolution. In previous studies, amplitude ratio of PKiKP/PcP at short distances and PKiKP/P at larger distances are used to constrain the shear veloc- ity and density contrast, and shear velocity in the top inner core is found to be substantially smaller than the PREM prediction. Here we present a large dataset of PKiKP/P amplitude ratio measured on 420 seismic records at ILAR array in Alaska for the distance range of 800-90~, where the amplitude ra- tio is sensitive to shear velocity and density contrast. At high frequency （up to 6 Hz）, mantle attenuation is found to have substantial effects on PKiKP/P. After the attenuation effects are taken into account, we find that the density contrast is about 0.2-1.0 g/cm3, and shear velocity of inner core is 3.2-4.0 km/s, close to the PREM （Preliminary Reference Earth Model） prediction （0.6 g/cm3 and 3.5 kin/s, respec- tively）. The relatively high shear velocity in inner core does not require large quantities of defects or melts as proposed in previous studies.

关键词： inner core boundary shear velocity of inner core density contrast core phase.

Optimal carrier-smoothed-code algorithm for dual-frequency GPS data

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Progress in Natural Science:Materials International 2008年第5期18卷 591-594页

作者： Jianfeng Guo a,b, Jikun Ou a, Yunbin Yuan a, Haitao Wang a a Key Laboratory of geodynamics, Institute of geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China b Institute of Science, Information Engineering University, Zhengzhou 450001, China Key Laboratory of geodynamics Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China Institute of Science Information Engineering University Zhengzhou 450001 China

Carrier-smoothed-code (CSC) algorithm is an e ective pseudorange multipath mitigation technique, which can alleviate the compu- tational burden and reduce the communication bandwidth needed for the transmission of GPS observations. This paper presents an improved Hatch lter and addresses the optimal CSC algorithm for dual-frequency GPS data based on the optimal parameter estimation theory. The smoothed observations have the same information content as that of the raw dual-frequency GPS data from which these are derived. Consequently, the optimal CSC algorithm is equivalent to the uncombined algorithm. Theoretical analyses show that the data precision of the optimal CSC algorithm is better than that of Hatch lter and its improved version.

关键词： GPS Carrier-smoothed-code algorithm Hatch lter Time-invariant combinations

Crustal structure of the central Tibetan plateau and geological interpretation

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Earthquake Science 2012年第5期25卷 363-370页

作者： Can Ge Youshun Sun M Nafi Toksz Yingcai Zheng Yong Zheng Xiong Xiong Diming Yu State Key Laboratory of geodesy and Earth geodynamics Institute of Geodesy and GeophysicsChinese Academy of Sciences University of Chinese Academy of Sciences Department of Earth Atmosphere and Planetary SciencesMassachusetts Institute of Technology

Based on teleseismic data obtained from 225 stations from two networks in the central Tibetan plateau, we have generated detailed crustal structure images using P-wave receiver function techniques with more accurate piercing-depth-correction and time-depth-correction than what have previously been available. Our images indicate an undulatory Moho beneath the Tibetan plateau with a steep jump beneath the northern Himalaya, and obviously different structures in proximity to the Bangong-Nujiang suture. In several sections of the Tibetan plateau, the lower crust is characterized by pervasive high-velocity regions, which are consistent with the preservation of eclogite bodies beneath the plateau, whose presence affects the dynamics of the Tibetan plateau.

关键词： receiver function crustal structure Tibetan plateau

Gravity distribution characteristics and their relationship with the distribution of earthquakes and tectonic units in the Northe South seismic belt, China

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geodesy and geodynamics 2015年第3期6卷 194-202页

作者： Wu Guiju Tan Hongbo Zou Zhengbo Yang Guangliang Shen Chongyang Key Laboratory of Earthquake geodesy Institute of Seismology China Earthquake Administration Wuhan Base of Institute of geodynamics China Earthquake Administration

The Northe South Seismic Belt(NSSB) is a Chinese tectonic boundary with a very complex structure, showing a sharp change in several geophysical field characteristics. To study these characteristics and their relationship with the distribution of earthquakes and faults in the study area, we first analyze the spatial gravity anomaly to achieve the Bouguer gravity anomaly(EGM2008 BGA) and the regional gravity survey Bouguer gravity ***, we ascertain the Moho depth and crustal thickness of the study area using interface inversion with the control points derived from the seismic and magnetotelluric sounding profiles achieved in recent years. In this paper, we summarize the relief, trend, Moho gradient, and crustal nature, in addition to their relationship with the distribution of earthquakes and faults in the study area. The findings show that earthquakes with magnitudes greater than Ms7.0 are mainly distributed in the Moho Bouguer anomaly variation belt and faults. The results of the study are important for future research on tectonic characteristics, geological and geophysical surveys, and seismicity patterns.

关键词： Spatial gravity data Bouguer gravity anomaly North

Isostatic anomaly characteristics and tectonism of the New Britain Trench and neighboring Papua New Guinea

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geodesy and geodynamics 2018年第5期9卷 404-410页

作者： Guangliang Yang Chongyang Shen Jiapei Wang Songbai Xuan Guiju Wu Hongbo Tan Key Laboratory of Earthquake geodesy Institute of Seismology China Earthquake Administration Wuhan Base of Institute of geodynamics China Earthquake Administration

In this paper, we calculated Bouguer gravity anomalies and Airy-Heiskanen isostatic anomalies in the New Britain Trench and surrounding areas of Papua New Guinea. The calculations are based on a topographic model and a gravity anomaly model from the Scripps Institute of Oceanography. Characteristics of the isostatic anomaly and the earthquake dynamic environment of this region are analyzed,and the results show that there are obvious differences in the isostatic state between each block in the region. Tectonic movements are very intense in regions with high positive or negative isostatic gravity anomalies, and a number of sub-plates in this area are driven by external tectonic action, such as plate subduction and thrusting, of the Pacific, Indo-Australian and Eurasian plates. From the distribution of the isostatic gravity anomaly, the tectonic action of anti-isostatic movement obviously is the main source of power. Based on isostatic gravity and spatial distribution of earthquakes in the region, it is obvious that further contraction of the Indo-Australian Plate will result in the southwestern part of the Solomon Plate becoming part of the Owen Stanley thrust belt, and the northern part will enter the lower part of the Bismarck Plate. The eastern part of the Solomon Plate will enter the front of the Pacific Plate, resulting in northward and eastward migration of significant earthquakes along the Solomon Plate.

关键词： Papua New Guinea New Britain Trench Earthquake Bouguer gravity anomaly Isostatic gravity anomaly

Characteristics of isostatic gravity anomaly in Sichuan-Yunnan region,China

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geodesy and geodynamics 2017年第4期8卷 238-245页

作者： Bingcheng Liu Yiyan Zhou Guangliang Yang Key Laboratory of Earthquake geodesy Institute of SeismologyChina Earthquake Administration Wuhan Base of Institute of geodynamics China Earthquake Administration

Sichuan-Yunnan region in China, a tectonic transition belt where earthquakes occurred frequently and intensely, has a distinct variation characteristic of gradient zone of Bouguer gravity anomaly （BGA）. Many deep faults and epicenters of severe earthquake scatter along the BGA gradient zones. Here we apply two forward models （Airy model and Vening Meinesz model） of isostatic gravity mechanisms （local versus regional） in this region to calculated the isostatic gravity anomaly （IGA）. Afterwards, the relationship between IGA and distribution of faults as well as seismicity is also illustrated. The IGA results show that the two models are similar and most parts of the study area are in an isostatic state. Most featured faults are distributed along the steep anomaly gradient zones; earthquakes tend to occur in the non-isostatic area and steep gradient belt of IGA. The distribution of root thickness based on regional mechanism can be associated with the main trend of BGA variation. The regional mechanism is more plausible and closer to the reality because of its relatively further consideration of the horizontal forces derived from adjacent particles in the crust. Then we analyze the effect of isostasy on the tectonic movements and find that the isostatic adjustment is not the main cause of the continuous uplift process of Longmenshan Mountain fault zone. which is due to the Indian-Eurasian continental collision.

关键词： lsostatic gravity anomaly Isostasy Airy model Vening meinesz model Sichuan-Yunnan region Fault Earthquake