The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Rene Forsberg - One of the best experts on this subject based on the ideXlab platform.
-
from discrete Gravity Survey data to a high resolution Gravity field representation in the nordic baltic region
Marine Geodesy, 2017Co-Authors: Silja Mardla, Rene Forsberg, Jonas Agre, Gabriel Strykowski, Tonis Oja, Artu Ellma, Mirjam Ilkerkoivula, O C D Omang, Eimuntas Parseliūnas, Ivars LiepinsAbstract:ABSTRACTThe deduction of a regularly spaced Gravity anomaly grid from scattered Survey data is studied, addressing mainly two aspects: reduction of Gravity to anomalies and subsequent interpolation by various methods. The problem is illustrated in a heterogeneous study area and contrasting test areas including mountains, low terrains, and a marine area. Provided with realistic error estimates, Least Squares Collocation interpolation of Residual Terrain Model anomalies yields the highest quality Gravity grid. In most cases, the Bouguer reduction and other interpolation methods tested are equally viable. However, spline-based interpolation should be avoided in marine areas with trackwise Survey data.
-
geological mapping of sabah malaysia using airborne Gravity Survey
Borneo Science The Journal of Science and Technology, 2016Co-Authors: Ahmad Fauzi Nordi, Rene Forsberg, Arne Vestergaard Olese, Hassa Jamil, Mohd Noo Isa, Azhari Mohamed, Sanudi Tahi, Aba Musta, Jens Emil Nielse, Abd Majid A KadiAbstract:Airborne gravimetry is an effective tool for mapping local Gravity fields using a combination of airborne sensors, aircraft and positioning systems. It is suitable for Gravity Surveys over difficult terrains and areas mixed with land and ocean. This paper describes the geological mapping of Sabah using airborne Gravity Surveys. Airborne Gravity data over land areas of Sabah has been combined with the marine airborne Gravity data to provide a seamless land-to-sea Gravity field coverage in order to produce the geological mapping. Free-air and Bouguer anomaly maps (density 2.67 g/cm 3 ) have been derived from the airborne data both as simple ad-hoc plots (at aircraft altitude), and as final plots from the downward continued airborne data, processed as part of the geoids determination. Data are gridded at 0.025 degree spacing which is about 2.7 km and the data resolution of the filtered airborne Gravity data were 5-6 km. The airborne Gravity Survey database for land and marine areas has been compiled using ArcGIS geodatabase format in order to produce the update geological map of Sabah.
-
geoid of nepal from airborne Gravity Survey
2011 IAG General Assembly, 2014Co-Authors: Rene Forsberg, Arne Vestergaard Olese, Indridi Einarsso, Niraj Manandha, Kalya ShreshtaAbstract:An airborne Gravity Survey of Nepal was carried out December 2010 in a cooperation between DTU-Space, Nepal Survey Department, and NGA, USA. The entire country was flown with Survey lines spaced 6 nm with a Beech King Air aircraft, with a varying flight altitude from 4 to 10 km. The Survey operations were a major challenge due to excessive jet streams at altitude as well as occasional excessive mountain waves. Despite the large 400 mGal + range of Gravity anomaly changes from the Indian plains to the Tibetan Plateau, results appear accurate to few mGal, with proper evaluation from cross-overs complicated by the high varying flight altitudes. Using a downward continuation scheme based on blocked least-squares collocation, a new geoid of Nepal was computed by Fourier methods. The new geoid shows large changes to EGM08, illustrating the impact of the new data. The new geoid is compared to limited GPS-levelling data as well as recent GPS-heights of Mt. Everest, and the new data also provide an independent validation of GOCE Gravity field models at the local ∼100 km resolution scale.
-
geoid model and altitude at mount aconcagua region argentina from airborne Gravity Survey
2014Co-Authors: Cristina M Pacino, Rene Forsberg, Arne Vestergaard Olese, Eric Jage, Silvia Miranda, Luis LenzanoAbstract:Aconcagua is part of the Southern Andes in the Argentine Province of Mendoza and it is the highest mountain in the Americas. The Aconcagua region is mostly inaccessible for land Surveys. The existing Gravity data are sparsely distributed, and mainly along the route currently used to climb the mountain. Gravity data are needed for applications such as geoid modeling, vertical datum determination and geological study. In 2010, a high-altitude Survey (between 7,000 and 8,000 m above sea level), covering the entire area of Aconcagua was performed. This Survey was done within the framework of IAG Project “Gravity and Geoid in South America”. Free Air anomalies were computed and compared to Earth Gravitational Model 2008 (EGM08), degree 2190 at the flight altitude. The residuals can be attributed to the fact that the airborne data carries a lot of new Gravity information not represented in the EGM08 model. A geoid model was computed from those airborne Gravity anomalies and land gravimetry data. A remove-restore method was used for terrain and global spherical harmonic reference models, with the residual Gravity field signal downward continued by least-squares collocation, and the geoid and quasi-geoid computed by spherical Fourier methods. The N value at Aconcagua’s summit was combined with the ellipsoidal height observed at the summit GPS station to obtain the orthometric height above sea level, confirming the most recent triangulated summit height of 6,960 m.
-
geodetic and geophysical results from a taiwan airborne Gravity Survey data reduction and accuracy assessment
Journal of Geophysical Research, 2007Co-Authors: Cheinway Hwang, Rene Forsberg, Yushe Hsiao, Hsuan Chang Shih, Ming Yang, Kwo Hwa Che, Arne Vestergaard OleseAbstract:[1] An airborne Gravity Survey was conducted over Taiwan using a LaCoste and Romberg (LCR) System II air-sea gravimeter with Gravity and global positioning system (GPS) data sampled at 1 Hz. The aircraft trajectories were determined using a GPS network kinematic adjustment relative to eight GPS tracking stations. Long-wavelength errors in position are reduced when doing numerical differentiations for velocity and acceleration. A procedure for computing resolvable wavelength of error-free airborne gravimetry is derived. The accuracy requirements of position, velocity, and accelerations for a 1-mgal accuracy in Gravity anomaly are derived. GPS will fulfill these requirements except for vertical acceleration. An iterative Gaussian filter is used to reduce errors in vertical acceleration. A compromising filter width for noise reduction and Gravity detail is 150 s. The airborne Gravity anomalies are compared with surface values, and large differences are found over high mountains where the Gravity field is rough and surface data density is low. The root mean square (RMS) crossover differences before and after a bias-only adjustment are 4.92 and 2.88 mgal, the latter corresponding to a 2-mgal standard error in Gravity anomaly. Repeatability analyses at two Survey lines suggest that GPS is the dominating factor affecting the repeatability. Fourier transform and least-squares collocation are used for downward continuation, and the latter produces a better result. Two geoid models are computed, one using airborne and surface Gravity data and the other using surface data only, and the former yields a better agreement with the GPS-derived geoidal heights. Bouguer anomalies derived from airborne Gravity by a rigorous numerical integration reveal important tectonic features.
Arne Vestergaard Olese - One of the best experts on this subject based on the ideXlab platform.
-
geological mapping of sabah malaysia using airborne Gravity Survey
Borneo Science The Journal of Science and Technology, 2016Co-Authors: Ahmad Fauzi Nordi, Rene Forsberg, Arne Vestergaard Olese, Hassa Jamil, Mohd Noo Isa, Azhari Mohamed, Sanudi Tahi, Aba Musta, Jens Emil Nielse, Abd Majid A KadiAbstract:Airborne gravimetry is an effective tool for mapping local Gravity fields using a combination of airborne sensors, aircraft and positioning systems. It is suitable for Gravity Surveys over difficult terrains and areas mixed with land and ocean. This paper describes the geological mapping of Sabah using airborne Gravity Surveys. Airborne Gravity data over land areas of Sabah has been combined with the marine airborne Gravity data to provide a seamless land-to-sea Gravity field coverage in order to produce the geological mapping. Free-air and Bouguer anomaly maps (density 2.67 g/cm 3 ) have been derived from the airborne data both as simple ad-hoc plots (at aircraft altitude), and as final plots from the downward continued airborne data, processed as part of the geoids determination. Data are gridded at 0.025 degree spacing which is about 2.7 km and the data resolution of the filtered airborne Gravity data were 5-6 km. The airborne Gravity Survey database for land and marine areas has been compiled using ArcGIS geodatabase format in order to produce the update geological map of Sabah.
-
geoid of nepal from airborne Gravity Survey
2011 IAG General Assembly, 2014Co-Authors: Rene Forsberg, Arne Vestergaard Olese, Indridi Einarsso, Niraj Manandha, Kalya ShreshtaAbstract:An airborne Gravity Survey of Nepal was carried out December 2010 in a cooperation between DTU-Space, Nepal Survey Department, and NGA, USA. The entire country was flown with Survey lines spaced 6 nm with a Beech King Air aircraft, with a varying flight altitude from 4 to 10 km. The Survey operations were a major challenge due to excessive jet streams at altitude as well as occasional excessive mountain waves. Despite the large 400 mGal + range of Gravity anomaly changes from the Indian plains to the Tibetan Plateau, results appear accurate to few mGal, with proper evaluation from cross-overs complicated by the high varying flight altitudes. Using a downward continuation scheme based on blocked least-squares collocation, a new geoid of Nepal was computed by Fourier methods. The new geoid shows large changes to EGM08, illustrating the impact of the new data. The new geoid is compared to limited GPS-levelling data as well as recent GPS-heights of Mt. Everest, and the new data also provide an independent validation of GOCE Gravity field models at the local ∼100 km resolution scale.
-
geoid model and altitude at mount aconcagua region argentina from airborne Gravity Survey
2014Co-Authors: Cristina M Pacino, Rene Forsberg, Arne Vestergaard Olese, Eric Jage, Silvia Miranda, Luis LenzanoAbstract:Aconcagua is part of the Southern Andes in the Argentine Province of Mendoza and it is the highest mountain in the Americas. The Aconcagua region is mostly inaccessible for land Surveys. The existing Gravity data are sparsely distributed, and mainly along the route currently used to climb the mountain. Gravity data are needed for applications such as geoid modeling, vertical datum determination and geological study. In 2010, a high-altitude Survey (between 7,000 and 8,000 m above sea level), covering the entire area of Aconcagua was performed. This Survey was done within the framework of IAG Project “Gravity and Geoid in South America”. Free Air anomalies were computed and compared to Earth Gravitational Model 2008 (EGM08), degree 2190 at the flight altitude. The residuals can be attributed to the fact that the airborne data carries a lot of new Gravity information not represented in the EGM08 model. A geoid model was computed from those airborne Gravity anomalies and land gravimetry data. A remove-restore method was used for terrain and global spherical harmonic reference models, with the residual Gravity field signal downward continued by least-squares collocation, and the geoid and quasi-geoid computed by spherical Fourier methods. The N value at Aconcagua’s summit was combined with the ellipsoidal height observed at the summit GPS station to obtain the orthometric height above sea level, confirming the most recent triangulated summit height of 6,960 m.
-
geodetic and geophysical results from a taiwan airborne Gravity Survey data reduction and accuracy assessment
Journal of Geophysical Research, 2007Co-Authors: Cheinway Hwang, Rene Forsberg, Yushe Hsiao, Hsuan Chang Shih, Ming Yang, Kwo Hwa Che, Arne Vestergaard OleseAbstract:[1] An airborne Gravity Survey was conducted over Taiwan using a LaCoste and Romberg (LCR) System II air-sea gravimeter with Gravity and global positioning system (GPS) data sampled at 1 Hz. The aircraft trajectories were determined using a GPS network kinematic adjustment relative to eight GPS tracking stations. Long-wavelength errors in position are reduced when doing numerical differentiations for velocity and acceleration. A procedure for computing resolvable wavelength of error-free airborne gravimetry is derived. The accuracy requirements of position, velocity, and accelerations for a 1-mgal accuracy in Gravity anomaly are derived. GPS will fulfill these requirements except for vertical acceleration. An iterative Gaussian filter is used to reduce errors in vertical acceleration. A compromising filter width for noise reduction and Gravity detail is 150 s. The airborne Gravity anomalies are compared with surface values, and large differences are found over high mountains where the Gravity field is rough and surface data density is low. The root mean square (RMS) crossover differences before and after a bias-only adjustment are 4.92 and 2.88 mgal, the latter corresponding to a 2-mgal standard error in Gravity anomaly. Repeatability analyses at two Survey lines suggest that GPS is the dominating factor affecting the repeatability. Fourier transform and least-squares collocation are used for downward continuation, and the latter produces a better result. Two geoid models are computed, one using airborne and surface Gravity data and the other using surface data only, and the former yields a better agreement with the GPS-derived geoidal heights. Bouguer anomalies derived from airborne Gravity by a rigorous numerical integration reveal important tectonic features.
-
airborne Gravity Survey of the north greenland continental shelf
2001Co-Authors: Rene Forsberg, Arne Vestergaard Olese, K KelleAbstract:An airborne Gravity Survey has been carried out 1998–99 to cover the ice-covered parts of the seas around northern and north-eastern Greenland. The aeroGravity Survey has been done by a Danish-Norwegian aeroGravity system setup, based on a Lacoste and Romberg “S” gravimeter. A Twin-Otter aircraft has been used, capable of low and slow flights, yielding airborne Gravity measurements of relatively high accuracy and resolution. Crossover adjustments and comparisons to independent marine Gravity data indicate accuracies of 2 mGal r.m.s., at a resolution of 6–7 km. This kind of accuracy level corresponds to relative geoid errors around 10 cm across the coastal region.
Mark A Zumberge - One of the best experts on this subject based on the ideXlab platform.
-
results from sleipner Gravity monitoring updated density and temperature distribution of the co2 plume
Energy Procedia, 2011Co-Authors: Havard Alnes, Ola Eiken, Scott L Nooner, Glenn S Sasagawa, Torkjell Stenvold, Mark A ZumbergeAbstract:Abstract To help monitor the evolution of stored CO 2 , we have made precision seafloor Gravity measurements at 30 seafloor stations above the Sleipner CO 2 plume in the years 2002, 2005 and 2009. Each epoch of Gravity data has an intra-Survey repeatability of about 3 μGal (standard deviation), obtained using state-of-the-art instrumentation on top of pre-deployed seafloor benchmarks, with typically three visits on each location during a Survey. We used three relative quartz-spring Scintrex CG-5 gravimeters in a unique offshore instrument package. Ocean tidal fluctuations and benchmark depths were determined using both pressure gauges on the Gravity Survey tool and stationary reference pressure gauges on the seafloor. We analyzed and accounted for multiple sources of changes in Gravity to obtain an estimate of in situ CO 2 density. First, the injected CO 2 , 5.88 million tonnes during this time period, displaces denser formation water, causing a negative Gravity change above the plume. This is the signal of interest for this study. At the same time, hydrocarbon gas production and water influx into the deep, nearby gas reservoir cause an increase in Gravity of higher amplitude and longer wavelength. Finally, by observing vertical depth changes of the seafloor benchmarks between Surveys to mm precision, we quantified vertical benchmark movements caused by sediment scouring. Some of the benchmarks have experienced more than 10 cm vertical movement over the 7 year duration of the experiment, and erosional topography can be seen in a >10 m broad area around some of the benchmarks. The shifting sediment can also cause a change in the observed vertical Gravity gradient. We inverted the Gravity changes for simultaneous contributions from: (i) injected CO 2 in the Utsira Formation, (ii) water flow into the Sleipner gas reservoir, and (iii) vertical benchmark movements. We estimate the part of the change in Gravity caused by CO 2 injection to be up to 12 μGal. If we assume a geometry of the plume as seen in 4D seismic data, the best match to the 30 stations requires an average CO 2 density of 720±80 kg/ m 3 , neglecting dissolution of CO 2 into the formation water. While the CO 2 in the Utsira Fm. at Sleipner is supercritical, it is fairly close to the critical point; therefore only a slight increase in temperature could lower the density significantly. Density is also sensitive to impurities, which make up 1–2% of the injected material at Sleipner and reduce the density slightly. In the absence of down hole gauges in the injection well, we estimate the well-bottom CO 2 temperature to be 48 °C and pressure to be hydrostatic (∼105 bar). These conditions give a calculated density of 485±10 kg/ m 3 at the perforation. Density is expected to increase away from the well as CO 2 cools down from contact with the cooler formation, up to a maximum of about 710 kg/ m 3 . The distribution of temperature and density within the plume is difficult to model exactly, but most of the CO 2 is expected to cool down to initial reservoir temperature (∼35.5 °C at the perforation) except for a central high-temperature region where CO 2 is still near the injection temperature. Because the undisturbed formation temperatures and the injection temperature are fairly well known, the 2002–2009 Gravity change can be used to constrain the rate of dissolution of CO 2 into the formation water. Dissolved CO 2 is invisible in seismic data. The contribution from gravimetric data could therefore be highly valuable for monitoring this process, which is important for long-term predictions of the CO 2 stored in the Utsira Fm. We give an upper bound on the dissolution rate of 1.8% per year.
-
a seafloor and sea surface Gravity Survey of axial volcano
Journal of Geophysical Research, 1990Co-Authors: Joh A Hildebrand, Mark A Zumberge, Mark J Stevenso, Philip T C Hamme, Robe L Parke, Philip J MeisAbstract:Seafloor and sea surface Gravity measurements are used to model the internal density structure of Axial Volcano. Seafloor measurements made at 53 sites within and adjacent to the Axial Volcano summit caldera provide constraints on the fine-scale density structure. Shipboard Gravity measurements made along 540 km of track line above Axial Volcano and adjacent portions of the Juan de Fuca ridge provide constraints on the density over a broader region and on the isostatic compensation. The seafloor Gravity anomalies give an average density of 2.7 g cm−3 for the uppermost portion of Axial Volcano, The sea surface Gravity anomalies yield a local compensation parameter of 23%, significantly less than expected for a volcanic edifice built on zero age lithosphere. Three-dimensional ideal body models of the seafloor Gravity measurements suggest that low-density material, with a density contrast of at least 0.15 g cm−3, may be located underneath the summit caldera. The data are consistent with low-density material at shallow depths near the southern portion of the caldera, dipping downward to the north. The correlation of shallow low-density material and surface expressions of recent volcanic activity (fresh lavas and high-temperature hydrothermal venting) suggests a zone of highly porous crust. Seminorm minimization modeling of the surface Gravity measurements also suggest a low-density region under the central portion of Axial Volcano. The presence of low-density material beneath Axial caldera suggests a partially molten magma chamber at depth.
Damien Do Couto - One of the best experts on this subject based on the ideXlab platform.
-
tectonic inversion of an asymmetric graben insights from a combined field and Gravity Survey in the sorbas basin
Tectonics, 2014Co-Authors: Damien Do Couto, Charles Gumiau, Romai Augie, Noemie Lebre, Nicolas FolcheAbstract:The formation of sedimentary basins in the Alboran domain is associated with the exhumation of metamorphic core complexes over a ca. 15 Ma period through a transition from regional late-orogenic extension to compression. An integrated study coupling field analysis and Gravity data acquisition was performed in the Sorbas basin in the southeastern Betic Cordillera. Detailed field observations revealed for the first time that extensional tectonics occurred before shortening in this basin. Two extensional events were recorded with NW-SE to N-S and NE-SW kinematics respectively; the first of which being likely responsible for the basin initiation. Tectonic inversion of the basin then occurred around 8 Ma in an overall ca. N-S shortening context. 2D-Gravity sections reveal that the basin acted as an active depocenter as the basin floor locally exceeding 2 km-depth is characterized by a marked asymmetric architecture. Based on this integrated study, we explore a new evolutionary scenario which can be used as a basis for interpretations of the Neogene tectonic history of the southeastern Betics.
Cheinway Hwang - One of the best experts on this subject based on the ideXlab platform.
-
fusion of time lapse Gravity Survey and hydraulic tomography for estimating spatially varying hydraulic conductivity and specific yield fields
Water Resources Research, 2017Co-Authors: Jui Pi Tsai, Cheinway Hwang, Tianchyi Jim Yeh, Ching Chung Cheng, Yuanyua Zha, Liangcheng Chang, Yu Li Wang, Yonghong HaoAbstract:Ministry of Science and Technology, Taiwan [MOST 104-2917-I-564-085, 105-2221-E-009-054-MY3, 105-2811-E-009-018]; Strategic Environmental Research and Development Program (SERDP) [ER-1365]; Environmental Security Technology Certification Program (ESTCP) [ER201212]; US National Science Foundation-Division of Earth Sciences [1014594]; Outstanding Oversea Professorship award through Jilin University from Department of Education, China; Global Expert award through Tianjin Normal University from the Thousand Talents Plan of Tianjin City
-
geodetic and geophysical results from a taiwan airborne Gravity Survey data reduction and accuracy assessment
Journal of Geophysical Research, 2007Co-Authors: Cheinway Hwang, Rene Forsberg, Yushe Hsiao, Hsuan Chang Shih, Ming Yang, Kwo Hwa Che, Arne Vestergaard OleseAbstract:[1] An airborne Gravity Survey was conducted over Taiwan using a LaCoste and Romberg (LCR) System II air-sea gravimeter with Gravity and global positioning system (GPS) data sampled at 1 Hz. The aircraft trajectories were determined using a GPS network kinematic adjustment relative to eight GPS tracking stations. Long-wavelength errors in position are reduced when doing numerical differentiations for velocity and acceleration. A procedure for computing resolvable wavelength of error-free airborne gravimetry is derived. The accuracy requirements of position, velocity, and accelerations for a 1-mgal accuracy in Gravity anomaly are derived. GPS will fulfill these requirements except for vertical acceleration. An iterative Gaussian filter is used to reduce errors in vertical acceleration. A compromising filter width for noise reduction and Gravity detail is 150 s. The airborne Gravity anomalies are compared with surface values, and large differences are found over high mountains where the Gravity field is rough and surface data density is low. The root mean square (RMS) crossover differences before and after a bias-only adjustment are 4.92 and 2.88 mgal, the latter corresponding to a 2-mgal standard error in Gravity anomaly. Repeatability analyses at two Survey lines suggest that GPS is the dominating factor affecting the repeatability. Fourier transform and least-squares collocation are used for downward continuation, and the latter produces a better result. Two geoid models are computed, one using airborne and surface Gravity data and the other using surface data only, and the former yields a better agreement with the GPS-derived geoidal heights. Bouguer anomalies derived from airborne Gravity by a rigorous numerical integration reveal important tectonic features.
