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On the Accuracy Assessment of the Latest Releases of GOCE Satellite-Based Geopotential Models with EGM2008 and Terrestrial GPS/Levelling and Gravity Data over Egypt 被引量:2
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作者 Mohamed El-Ashquer Basem Elsaka Gamal El-Fiky 《International Journal of Geosciences》 2016年第11期1323-1344,共23页
The Global Geopotential Models (GGMs) of GOCE (Gravity Recovery and steady- state Ocean Circulation Explorer) differ globally as well as regionally in their accuracy and resolution based on the maximum degree and orde... The Global Geopotential Models (GGMs) of GOCE (Gravity Recovery and steady- state Ocean Circulation Explorer) differ globally as well as regionally in their accuracy and resolution based on the maximum degree and order (d/o) of the fully normalized spherical harmonic (SH) coefficients, which express each GGM. The main idea of this study is to compare the free-air gravity anomalies and quasi geoid heights determined from several recent GOCE-based GGMs with the corresponding ones from the Earth Gravitational Model 2008 (EGM2008) over Egypt on the one hand and with ground-based measurements on the other hand. The results regarding to the comparison of GOCE-based GGMs with terrestrial gravity and GPS/levelling data provide better improvement with respect to EGM2008. The 4th release GOCE-based GGM developed with the use of space-wise solution strategy (SPW_R4) approximates the gravity field well over the Egyptian region. The SPW_R4 model is accordingly suggested as a reference model for recovering the long wavelength (up to SH d/o 200) components of quasi geoid heights when modelling the gravimetric quasi-geoid over the Egypt. Finally, three types of transformation models: Four-, Five- and Seven-parameter transformations have been applied to reduce the data biases and to provide a better fitting of quasi geoid heights obtained from the studied GOCE-based GGMs to those from GPS/levelling data. These models reveal that the standard deviation of vertical datum over Egypt is at the level of about 32 cm. 展开更多
关键词 GOCE-Based GGMs Free-Air Gravity Anomalies GPS/Levelling Data Spectral Enhancement Method (SEM)
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Regional Evaluation of GOCE-Based GGMs with Ground-Based Gravity and GPS/Levelling Data over Egypt
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作者 Ahmed Saadon Basem Elsaka +1 位作者 Mohamed El-Ashquer Gamal El-Fiky 《International Journal of Geosciences》 2019年第6期652-668,共17页
The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has provided numerous Global Geopotential Models (GGMs) with different processing methodologies and model accuracies. In the curre... The gravity field and steady-state ocean circulation explorer (GOCE) satellite mission has provided numerous Global Geopotential Models (GGMs) with different processing methodologies and model accuracies. In the current contribution, the latest releases of GOCE-based GGMs are evaluated on the regional scale using the available terrestrial GPS/Levelling and gravity data collected over Egypt. To overcome the spectral inconsistency between the GOCE-based GGMs and the ground-based data, the spectral enhancement method (SEM) is applied. Five of GOCE-based GGMs have been used, namely GOSG01S, IGGT_R1, IfE_GOCE05s_ GO_CONS_GCF_2_SPW_R5 (SPW_R5 in the following) and NULP-02. The evaluation process of GOCE-based GGMs with the available ground data over Egypt considering the SEM method shows remarkable improvements obtained from the SPW_R5 model. The model provides lower differences of the standard deviations with respect to the EGM2008 and the other applied geopotential gravity models as well as the applied ground-based gravity and GPS/Levelling data. The findings regarding the ground-based data show obvious reductions of about 15.16% and 32.22% achieved by the GOCE-based model in term of standard deviations differences of gravity anomalies and geoid heights, respectively. Therefore, the SPW_R5 model is recommended to be applied as a reference model for compensating the long-to-short wavelength (up to spherical harmonics degree/order 280) components when modelling the gravimetric geoid over Egypt. 展开更多
关键词 GOCE-Based GGMs GRAVITY Anomalies GNSS/Levelling Spectral Enhancement Method (SEM)
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Impact of the terrestrial reference frame on the determination of the celestial reference frame
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作者 Maria Karbon Santiago Belda Tobias Nilsson 《Geodesy and Geodynamics》 2019年第1期58-71,共14页
Currently three up-to-date Terrestrial Reference Frames(TRF) are available, the ITRF2014 from IGN, the DTRF2014 from DGFI-TUM, and JTRF2014 from JPL. All use the identical input data of space-geodetic station position... Currently three up-to-date Terrestrial Reference Frames(TRF) are available, the ITRF2014 from IGN, the DTRF2014 from DGFI-TUM, and JTRF2014 from JPL. All use the identical input data of space-geodetic station positions and Earth orientation parameters, but the concept of combining these data is fundamentally different. The IGN approach is based on the combination of technique solutions, while the DGFI is combining the normal equation systems. Both yield in reference epoch coordinates and velocities for a global set of stations. JPL uses a Kalman filter approach, realizing a TRF through weekly time series of geocentric coordinates. As the determination of the CRF is not independent of the TRF and vice versa, the choice of the TRF might impact on the CRF, Within this work we assess this effect.We find that the estimated Earth orientation parameter(EOP) from DTRF2014 agree best with those from ITRF2014, the EOP resulting from JTRF2014 show besides clear yearly signals also some artifacts linked to certain stations. The estimated source position time series however, agree with each other better than ±1 μas. When fixing EOP and station positions we can see the maximal effect of the TRF on the CRF. Here large systematics in position as well as proper motion arise. In case of ITRF2008 they can be linked to the missing data after 2008. By allowing the EOP and stations to participate in the adjustment,the agreement increases, however, systematics remain. 展开更多
关键词 REFERENCE FRAMES CRF TRF DTRF2014 JTRF2014 ITRF2014
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基于GRACE的空间约束方法监测华北平原地下水储量变化 被引量:62
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作者 冯伟 王长青 +3 位作者 穆大鹏 钟敏 钟玉龙 许厚泽 《地球物理学报》 SCIE EI CAS CSCD 北大核心 2017年第5期1630-1642,共13页
华北平原作为我国重要的工农业基地和政治经济中心,面临着严重的水资源危机.因此,开展对华北平原地下水储量变化的监测工作具有重要现实意义与科学价值.本文基于GRACE重力卫星的空间约束方法,研究了华北平原地下水储量变化的时空分布规... 华北平原作为我国重要的工农业基地和政治经济中心,面临着严重的水资源危机.因此,开展对华北平原地下水储量变化的监测工作具有重要现实意义与科学价值.本文基于GRACE重力卫星的空间约束方法,研究了华北平原地下水储量变化的时空分布规律,并与地面水井实测与地下水模型结果进行了综合比较和分析.结果表明:2002-2014年,华北平原地下水存在明显的长期亏损,GRACE估计的亏损速率为-7.4±0.9 km^3·a^(-1),而地面水井资料估计的浅层地下水亏损速率为-1.2 km^3·a^1,对比两者之间的差异可以发现,华北平原的地下水亏损以深层地下水为主.2002-2008年,GRACE估计的华北平原地下水亏损速率为-5.3±2.2 km^3·a^(-1),这与华北平原两个地下水模型得到的平均亏损速率-5.4 km^3·a^(-1)十分吻合.通过华北平原区域地下水模型的独立验证,说明GRACE可以有效评估华北平原的地下水储量变化趋势.除了长期亏损的趋势项之外,华北平原地下水还存在明显的年际变化特征,并与该地区年降雨量变化特征一致.在降雨偏少的2002年、2005-2009年和2014年,华北平原地下水储量显著减少.在空间分布上,GRACE结果表明,华北平原的地下水储量减少主要发生在山前平原和中部平原区,这也与水井实测资料和区域地下水模型结果较为吻合.与GRACE和区域地下水模型相比,目前的全球水文模型仍无法准确估计华北平原地下水变化的空间分布和亏损速率.上述研究表明,GRACE提供了评估华北平原地下水储量变化的重要监测手段. 展开更多
关键词 卫星重力 空间约束 华北平原 地下水储量
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Quality monitoring of real-time GNSS precise positioning service system 被引量:1
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作者 Run Ji Xinyuan Jiang +3 位作者 Xinghan Chen Huizhong Zhu Maorong Ge Frank Neitzel 《Geo-Spatial Information Science》 SCIE EI CSCD 2023年第1期1-15,共15页
The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centi... The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively. 展开更多
关键词 Global Navigation Satellite System(GNSS) real-time precise positioning quality monitoring precise point positioning satellite product bias
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A dynamic holographic modelling method of digital twin scenes for bridge construction 被引量:1
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作者 Jianlin Wu Jun Zhu +8 位作者 Jinbin Zhang Pei Dang Weilian Li Yukun Guo Lin Fu Jianbo Lai Jigang You YaKun Xie Ce Liang 《International Journal of Digital Earth》 SCIE EI 2023年第1期2404-2425,共22页
Holographic projection technology can provide a more intuitive and efficient visualization effect for a digital twin bridge construction scene.However,pre-rendering methods in the existing research work are usually us... Holographic projection technology can provide a more intuitive and efficient visualization effect for a digital twin bridge construction scene.However,pre-rendering methods in the existing research work are usually used to implement holographic visualization,which is static display.The above-mentioned methods for static display have many shortcomings,such as poor adaptability,low rendering efficiency and lack of real-time.A dynamic holographic modelling approach is proposed for the augmented visualization of digital twin scenes for bridge construction.Firstly,a dynamic segmentation algorithm with adaptive screen size was designed to high-efficiently generate holographic scenes.Secondly,a motion blur control method was designed to improve the rendering efficiency of holographic scenes according to human visual characteristics.Finally,a prototype system was developed,and the corresponding experimental analysis was completed.The experimental results show that the method proposed in this article can support adaptive screen size image segmentation and real-time generation of holographic scenes for bridge construction.The amount of scene data can be reduced to more than 30%,which significantly improves rendering efficiency and reduces glare. 展开更多
关键词 Bridge construction Digital twins Holographic scene Adaptive segmentation Rendering optimization
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A real 3D scene rendering optimization method based on region of interest and viewing frustum prediction in virtual reality
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作者 Pei Dang Jun Zhu +5 位作者 Jianlin Wu Weilian Li Jigang You Lin Fu Yiqun Shi Yuhang Gong 《International Journal of Digital Earth》 SCIE EI 2022年第1期1081-1100,共20页
As an important technology of digital construction,real 3D models can improve the immersion and realism of virtual reality(VR)scenes.The large amount of data for real 3D scenes requires more effective rendering method... As an important technology of digital construction,real 3D models can improve the immersion and realism of virtual reality(VR)scenes.The large amount of data for real 3D scenes requires more effective rendering methods,but the current rendering optimization methods have some defects and cannot render real 3D scenes in virtual reality.In this study,the location of the viewing frustum is predicted by a Kalman filter,and eye-tracking equipment is used to recognize the region of interest(ROI)in the scene.Finally,the real 3D model of interest in the predicted frustum is rendered first.The experimental results show that the method of this study can predict the frustrum location approximately 200 ms in advance,the prediction accuracy is approximately 87%,the scene rendering efficiency is improved by 8.3%,and the motion sickness is reduced by approximately 54.5%.These studies help promote the use of real 3D models in virtual reality and ROI recognition methods.In future work,we will further improve the prediction accuracy of viewing frustums in virtual reality and the application of eye tracking in virtual geographic scenes. 展开更多
关键词 Real 3D scene virtual reality Kalman filter region of interest viewing frustum
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Three-dimensional virtual representation for the whole process of dam-break floods from a geospatial storytelling perspective 被引量:1
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作者 Weilian Li Jun Zhu +3 位作者 Jan-Henrik Haunert Lin Fu Qing Zhu Youness Dehbi 《International Journal of Digital Earth》 SCIE EI 2022年第1期1637-1656,共20页
The objective of disaster scenes is to share location-based risk information to a large audience in an effective and intuitive way.However,current studies on three-dimensional(3D)representation for dam-break floods ha... The objective of disaster scenes is to share location-based risk information to a large audience in an effective and intuitive way.However,current studies on three-dimensional(3D)representation for dam-break floods have the following limitations:(1)they are lacking a reasonable logic to organize the whole process of dam-break floods,(2)they present information in a way that cannot be easily understood by laypersons.Geospatial storytelling helps to create exciting experiences and to explain complex relationships of geospatial phenomena.This article proposes a three-dimensional virtual representation method for the whole process of dam-break floods from a geospatial storytelling perspective.The creation of a storyline and a storytelling-oriented representation of dam-break floods are discussed in detail.Finally,a prototype system based on WebGL is developed to conduct an experiment analysis.The results of the experiment show that the proposed method can effectively support 3D representation of the spatiotemporal process of dam-break floods.Furthermore,the statistical results indicate that the storytelling is useful for assisting participants in understanding the occurrence and development of dam-break floods,and is applicable to the popularization of disaster science for the general public. 展开更多
关键词 Geospatial storytelling dam-break flood spatiotemporal process virtual representation 3D scene
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A raster-based typification method for multiscale visualization of building features considering distribution patterns 被引量:1
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作者 Yilang Shen Jingzhong Li +2 位作者 Ziqi Wang Rong Zhao Lu Wang 《International Journal of Digital Earth》 SCIE EI 2022年第1期249-275,共27页
In map multiscale visualization,typification is the process of replacing original objects,such as buildings,using a smaller number of objects while maintaining initial geometrical and distribution characteristics.Duri... In map multiscale visualization,typification is the process of replacing original objects,such as buildings,using a smaller number of objects while maintaining initial geometrical and distribution characteristics.During the past few decades,many vector-based methods for building typification have been developed,whereas raster-based methods have received less attention.In this paper,a new method for the typification of buildings with different distribution patterns called superpixel building typification(SUBT)is developed based on raster data.Using this method,buildings with different distribution patterns,such as linear,grid and irregular patterns,are first grouped by image connected component detection and superpixel analysis.Then,the new positions for building typification are determined by superpixel resegmentation.Finally,a new representation of the buildings is determined through analysis of the orientation and shape of the buildings in each superpixel.To test the proposed SUBT method,buildings from both cities and countrysides in China are applied to perform typification.The experimental results show that the proposed SUBT method can realize typification for buildings with linear,grid and irregular distributions while effectively maintaining the original distribution characteristics of the buildings. 展开更多
关键词 Building visualization building distribution pattern superpixel segmentation map generalization
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The synergies of SMAP enhanced and MODIS products in a random forest regression for estimating 1 km soil moisture over Africa using Google Earth Engine
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作者 Farzane Mohseni Amirhossein Ahrari +1 位作者 Jan-Henrik Haunert Carsten Montzka 《Big Earth Data》 EI 2024年第1期33-57,共25页
Due to the coarse scale of soil moisture products retrieved from passive microwave observations(SMPMW),several downscaling methods have been developed to enable regional scale applications.However,it can be challengin... Due to the coarse scale of soil moisture products retrieved from passive microwave observations(SMPMW),several downscaling methods have been developed to enable regional scale applications.However,it can be challenging for users to access final data products and algorithms,as well as managing different data sources and formats,various data processing methods,and the complexity of the workflows from raw data to information products.Here,the Google Earth Engine(GEE),which as of late offers SMPMW,is used to implement a workflow for retrieving 1 km SM at a depth of 0-5 cm using MODIS optical/thermal measurements,the SM_(PMW)coarse scale product,and a random forest regression.The proposed method was implemented on the African continent to estimate weekly SM maps.The results of this study were evaluated against in-situ measurements of three validation networks.Overall,in comparison to the original SM_(PMW)product,which was limited by a spatial resolution of only 9 km,this method is able to estimate SM at 1 km spatial resolution with acceptable accuracy(an average correlation coefficient of 0.64 and a ubRMSD of 0.069 m^(3)/m^(3)).The results show that the proposed method in GEE provides a precise estimation of SM with a higher spatial resolution across the entire continent. 展开更多
关键词 Soil moisture SMAP Google Earth Engine random forest regression MODIS
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An improved social force model (ISFM)-based crowd evacuation simulation method in virtual reality with a subway fire as a case study 被引量:2
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作者 Jinbin Zhang Jun Zhu +6 位作者 Pei Dang Jianlin Wu Yuxuan Zhou Weilian Li Lin Fu Yukun Guo Jigang You 《International Journal of Digital Earth》 SCIE EI 2023年第1期1186-1204,共19页
Crowd evacuation simulation using virtual reality(VR)is significant for digital emergency response construction.However,existing evacuation simulation studies suffer from poor adaptation to complex environments,ineffi... Crowd evacuation simulation using virtual reality(VR)is significant for digital emergency response construction.However,existing evacuation simulation studies suffer from poor adaptation to complex environments,inefficient evacuations,and poor simulation effects and do not fully consider the impacts of specific disaster environments on crowd evacuation.To more realistically express the crowd evacuation results obtained under the influence offire environments and the subjective consciousness of pedestrians in subway stations,we designed a dynamic pedestrian evacuation path planning method under multiple constraints,analysed the influences of an‘environmental role’and a‘subjective initiative’on crowd evacuation,established an improved social force model(ISFM)-based crowd evacuation simulation method in VR,developed a prototype system and conducted experimental analyses.The experimental results show that the crowd evacuation time of the ISFM is affected by the disaster severity.In simulation experiments without disaster scenarios,the improved model’s crowd evacuation efficiency improved by averages of 12.53%and 15.37%over the commercial Pathfinder software and the original social force model,respectively.The method described herein can effectively support real-time VR crowd evacuation simulation under multiexit and multifloor conditions and can provide technical support for emergency evacuation learning and management decision analyses involving subwayfires. 展开更多
关键词 Subway stationfire improved social force model crowd evacuation simulation virtual reality path planning
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Developing a web-based spatial decision support system for geothermal exploration at the Olkaria geothermal field 被引量:1
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作者 Daniel Mwaur Martin Kad 《International Journal of Digital Earth》 SCIE EI 2017年第11期1118-1145,共28页
Geothermal exploration is a complex process that spans a number of disciplines.Before a decision is made to drill a geothermal well,there is need for an extensive exploration process to determine the most suitable loc... Geothermal exploration is a complex process that spans a number of disciplines.Before a decision is made to drill a geothermal well,there is need for an extensive exploration process to determine the most suitable location.The process of evaluating and analyzing data from individual scientific disciplines can be complex and tedious.Attempts have been made at solving this problem using GIS-based tools but the uptake of these tools is often hindered by the limited knowledge of GIS by decision makers.This paper presents an approach for solving the geothermal exploration question through a web-based spatial decision support system(SDSS)that incorporates the various geosciences through a multi-criteria spatial decision analysis model.The results reveal a decision-making gap that is to be filled using a novel,automated exploration SDSS.This approach hypothesizes an easier and faster decision-making process.The research focuses on Olkaria,an active geothermal area in Kenya,East Africa and highlights a pragmatic approach to identifying priority areas for drilling.It evaluates contributions made by many disciplines in identifying potential sites ideal for harnessing geothermal energy and the gaps that emerge in an effort to synergize the results from the different disciplines. 展开更多
关键词 GIS SDSS GEOTHERMAL web based multi-criteria decision analysis
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