The availability of many high-degree Global Geopotential Models(GGMs), namely EGM2008, EIGEN-6C4,GECO, SGG-UGM-1, SGG-UGM-2, XGM2019e_2159, and GGMPlus, challenges users regarding which model is best for Vietnam. This...The availability of many high-degree Global Geopotential Models(GGMs), namely EGM2008, EIGEN-6C4,GECO, SGG-UGM-1, SGG-UGM-2, XGM2019e_2159, and GGMPlus, challenges users regarding which model is best for Vietnam. This study, therefore, evaluates their performance by comparing them with GNSS/leveling data over Vietnam. Results show that their absolute and relative performances are largely independent of topographic conditions and geographical location and can be ranked into three classes:(1)XGM2019e_2159 has the highest accuracy,(2) the models EIGEN-6C4, GECO, SGG-UGM-1, SGG-UGM-2, and GGMPlus, have a very similar level of medium accuracy, while(3) EGM2008 is found to be the least accurate. In an absolute sense, the differences between GNSS/leveling and EGM2008-based height anomalies have a standard deviation(STD) of 0.290 ± 0.010 m, whereas, for XGM2019e_2159, this is 0.156 ± 0.006 m.All other models have STDs of(0.18-0.19) ± 0.007 m. Regarding relative performance without fitting, all GGMs have comparable accuracies for baseline length of 5-20 km, while for baselines longer than 20 km,the STD of XGM2019e_2159 is 1.5 ppm-0.5 ppm(approximately 19%-40%) lower compared with EGM2008, and 0.5 ppm-0.25 ppm(approximately 7%-36%) lower compared with EIGEN6C4, GECO,SGG-UGM-1, SGG-UGM-2, and GGMPlus. In addition, the STDs decrease significantly from 20 to 12 ppm in the range of 5-10 km, slightly from 12 to 6 ppm for 10-35 km, very slightly from 6 to 2.5 ppm for35-200 km, and then remain almost unchanged for longer baselines. After fitting, the relative accuracies of all GGMs are at the same level with negligible STD/RMSE values. Furthermore, only EGM2008 experiences significant regional differences, while other GGMs show more homogeneous spatial variation of absolute accuracy over Vietnam. These findings can contribute to the development of local quasigeoid models in Vietnam and may be helpful with the improvement of GGMs in the future.展开更多
Satellite data sets are an asset in global gravity collections;their characteristics vary in coverage and resolution. New collections appear often, and the user must adapt fast to their characteristics. Their use in g...Satellite data sets are an asset in global gravity collections;their characteristics vary in coverage and resolution. New collections appear often, and the user must adapt fast to their characteristics. Their use in geophysical modeling is rapidly increasing;with this in mind we compare two of the most densely populated sets: EIGEN-6C4 and GGMplus. We characterize them in terms of their frequency histograms, Free Air anomalies, power spectrum, and simple Bouguer anomalies. The nature of the digital elevation models used for data reduction is discussed. We conclude that the GGMplus data set offers a better spatial resolution. To evaluate their effect in geophysical modelling, we chose an inland region with a prominent volcanic structure in which we perform 3D inversions of the respective Bouguer anomalies, obtaining density variations that in principle can be associated with the geologic materials and the structure of the volcanic edifice. Model results are analyzed along sections of the inverted data;we conclude that the GGMplus data set offers higher resolution in the cases analyzed.展开更多
The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures invo...The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.展开更多
文摘The availability of many high-degree Global Geopotential Models(GGMs), namely EGM2008, EIGEN-6C4,GECO, SGG-UGM-1, SGG-UGM-2, XGM2019e_2159, and GGMPlus, challenges users regarding which model is best for Vietnam. This study, therefore, evaluates their performance by comparing them with GNSS/leveling data over Vietnam. Results show that their absolute and relative performances are largely independent of topographic conditions and geographical location and can be ranked into three classes:(1)XGM2019e_2159 has the highest accuracy,(2) the models EIGEN-6C4, GECO, SGG-UGM-1, SGG-UGM-2, and GGMPlus, have a very similar level of medium accuracy, while(3) EGM2008 is found to be the least accurate. In an absolute sense, the differences between GNSS/leveling and EGM2008-based height anomalies have a standard deviation(STD) of 0.290 ± 0.010 m, whereas, for XGM2019e_2159, this is 0.156 ± 0.006 m.All other models have STDs of(0.18-0.19) ± 0.007 m. Regarding relative performance without fitting, all GGMs have comparable accuracies for baseline length of 5-20 km, while for baselines longer than 20 km,the STD of XGM2019e_2159 is 1.5 ppm-0.5 ppm(approximately 19%-40%) lower compared with EGM2008, and 0.5 ppm-0.25 ppm(approximately 7%-36%) lower compared with EIGEN6C4, GECO,SGG-UGM-1, SGG-UGM-2, and GGMPlus. In addition, the STDs decrease significantly from 20 to 12 ppm in the range of 5-10 km, slightly from 12 to 6 ppm for 10-35 km, very slightly from 6 to 2.5 ppm for35-200 km, and then remain almost unchanged for longer baselines. After fitting, the relative accuracies of all GGMs are at the same level with negligible STD/RMSE values. Furthermore, only EGM2008 experiences significant regional differences, while other GGMs show more homogeneous spatial variation of absolute accuracy over Vietnam. These findings can contribute to the development of local quasigeoid models in Vietnam and may be helpful with the improvement of GGMs in the future.
文摘Satellite data sets are an asset in global gravity collections;their characteristics vary in coverage and resolution. New collections appear often, and the user must adapt fast to their characteristics. Their use in geophysical modeling is rapidly increasing;with this in mind we compare two of the most densely populated sets: EIGEN-6C4 and GGMplus. We characterize them in terms of their frequency histograms, Free Air anomalies, power spectrum, and simple Bouguer anomalies. The nature of the digital elevation models used for data reduction is discussed. We conclude that the GGMplus data set offers a better spatial resolution. To evaluate their effect in geophysical modelling, we chose an inland region with a prominent volcanic structure in which we perform 3D inversions of the respective Bouguer anomalies, obtaining density variations that in principle can be associated with the geologic materials and the structure of the volcanic edifice. Model results are analyzed along sections of the inverted data;we conclude that the GGMplus data set offers higher resolution in the cases analyzed.
基金supported by IIMAS and the Geophysics Institute,both at UNAMmaterial support from both institutions.This research did not receive any specific grant from funding agencies in the public,commer-cial,or nonprofit sectors.
文摘The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.
