scholarly journals Evaluation of the BGM-3 sea gravity meter system onboard R/V Conrad

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1480-1493 ◽  
Author(s):  
Robin E. Bell ◽  
A. B. Watts
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Test Range ◽  
Free Air ◽  
Marine Gravity ◽  
Abrupt Changes ◽  
Spring Type ◽  
Free Air Gravity ◽  
Free Air Anomaly

The first Bell Aerospace BGM-3 Marine Gravity Meter System available for academic use was installed on R/V Robert D. Conrad in February, 1984. The BGM-3 system consists of a forced feedback accelerometer mounted on a gyrostabilized platform. Its sensor (requiring no cross‐coupling correction) is a significant improvement over existing beam and spring‐type sea gravimeters such as the GSS-2. A gravity survey over the Wallops Island test range together with the results of subsequent cruises allow evaluation of the precision, accuracy, and capabilities of the new system. Over the test range, the BGM-3 data were compared directly to data obtained by a GSS-2 meter onboard R/V Conrad. The rms discrepancy between free‐air gravity anomaly values at intersecting ship tracks of R/V Conrad was ±0.38 mGal for BGM-3 compared to ±1.60 mGal for the GSS-2. Moreover, BGM-3’s platform recovered from abrupt changes in ship’s heading more rapidly than did the platform of GSS-2. The principal factor limiting the accuracy of sea gravity data is navigation. Over the test range, where navigation was by Loran C and transit satellite, a two‐step filtering of the ship’s velocity and position was required to obtain an optimal Eötvös correction. A spectral analysis of 1 minute values of the Eötvös correction and the reduced free‐air gravity anomaly determined the filter characteristics. To minimize the coherence between the Eötvös and free‐air anomaly, it was necessary to prefilter the ship’s position and velocity. Using this procedure, reduced free‐air gravity anomalies with wavelengths as small as a few kilometers can be resolved.

scholarly journals Usporedba različitih pristupa Bouguer-ove redukcije na temelju satelitskih gravimetrijskih podataka

Geofizika ◽  
2020 ◽  
Vol 37 (2) ◽  
pp. 237-261
Author(s):  
Fan Luo ◽  
Xin Tao ◽  
Guangming Fu ◽  
Chong Zhang ◽  
Kun Zhang ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Gravitational Effect ◽  
Seismic Profile ◽  
Bouguer Gravity ◽  
Seismic Profiles ◽  
Satellite Gravity ◽  
Free Air ◽  
Free Air Gravity

Satellite gravity data are widely used in the field of geophysics to study deep structures at the regional and global scales. These data comprise free-air gravity anomaly data, which usually need to be corrected to a Bouguer gravity anomaly for practical application. Bouguer reduction approaches can be divided into two methods based on the coordinate system: the spherical coordinates method (SBG) and the Cartesian coordinates method; the latter is further divided into the CEBG and CBG methods, which do and do not include the Earth’s curvature correction. In this paper, free-air gravity anomaly data from the eastern Tibetan Plateau and its adjacent areas were used as the basic data to compare the CBG, CEBG, and SBG Bouguer gravity correction methods. The comparison of these three Bouguer gravity correction methods shows that the effect of the Earth’s curvature on the gravitational effect increases with increasing elevation in the study area. We want to understand the inversion accuracy for the data obtained by different Bouguer gravity reduction approaches. The depth distributions of the Moho were obtained by the interface inversion of the Bouguer gravity anomalies obtained by the CBG, CEBG, and SBG, and active seismic profiles were used as references for comparison and evaluation. The results show that the depths of the Moho obtained by the SBG inversion are more consistent with the measured seismic profile depths. Therefore, the SBG method is recommended as the most realistic approach in the process of global or regional research employing gravity data.

Empirical Determination of the Gravity Anomaly Covariance Function in Mountainous Areas

1980 ◽  
Vol 34 (3) ◽  
pp. 251-264 ◽  
Author(s):  
Gerard Lachapelle ◽  
K. P. Schwarz
Keyword(s):  
Gravity Anomaly ◽  
Covariance Function ◽  
Physical Geodesy ◽  
Gravity Anomalies ◽  
Mountainous Areas ◽  
The North ◽  
Regression Parameters ◽  
Free Air ◽  
Vening Meinesz ◽  
Free Air Gravity

An evaluation of the empirical gravity anomaly covariance function using over 95 000 surface gravity anomalies in the North American Western Cordillera was carried out. A regression analysis of the data exhibits a strong and quasi-linear correlation of free air gravity anomalies with heights. This height correlation is removed from the free air anomalies prior to the numerical evaluation of the gravity anomaly covariance function. This covariance function agrees well with that evaluated previously by the authors for the remainder of Canada. A possible use for such a covariance function of ‘height independent’ gravity anomalies in mountainous areas is described. First, the height independent gravity anomaly at a point of known height is evaluated by least squares prediction using neighboring measured height independent gravity anomalies. Secondly, the part caused by the height correlation is calculated using linear regression parameters estimated previously and added to the predicted height independent gravity anomaly to obtain a predicted standard free air anomaly. This technique can be used to densify the coverage of free air anomalies for subsequent use in integral formulas of physical geodesy, e.g., those of Stokes and Vening Meinesz. This method requires that point topographic heights be given on a grid.

Sea floor topography modeling by cumulating different types of gravity information

2020 ◽  
Author(s):  
Lucia Seoane ◽  
Benjamin Beirens ◽  
Guillaume Ramillien
Keyword(s):  
New England ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Sea Floor ◽  
Single Beam ◽  
Free Air ◽  
Free Air Gravity ◽  
Great Meteor Seamount

<p>We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.</p>

The Origin of Lunar Mascon Basins

Science ◽  
2013 ◽  
Vol 340 (6140) ◽  
pp. 1552-1555 ◽  
Author(s):  
H. J. Melosh ◽  
Andrew M. Freed ◽  
Brandon C. Johnson ◽  
David M. Blair ◽  
Jeffrey C. Andrews-Hanna ◽  
...  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Element Model ◽  
Isostatic Adjustment ◽  
Melt Pool ◽  
Free Air ◽  
Free Air Gravity ◽  
Bull's Eye ◽  
Gravity Recovery ◽  
The Impact

High-resolution gravity data from the Gravity Recovery and Interior Laboratory spacecraft have clarified the origin of lunar mass concentrations (mascons). Free-air gravity anomalies over lunar impact basins display bull’s-eye patterns consisting of a central positive (mascon) anomaly, a surrounding negative collar, and a positive outer annulus. We show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool. We used a hydrocode to simulate the impact and a self-consistent finite-element model to simulate the subsequent viscoelastic relaxation and cooling. The primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy, the lunar thermal gradient at the time of impact, the crustal thickness, and the extent of volcanic fill.

Gravitationally induced stresses at structural boundaries

1980 ◽  
Vol 17 (9) ◽  
pp. 1286-1291 ◽  
Author(s):  
A. K. Goodacre ◽  
H. S. Hasegawa
Keyword(s):  
Upper Mantle ◽  
Gravity Anomalies ◽  
Positive Anomaly ◽  
Crust And Upper Mantle ◽  
Free Air ◽  
Induced Stresses ◽  
Free Air Gravity ◽  
Free Air Anomaly ◽  
Structural Boundary ◽  
High Seismicity

Prominent gravity anomalies, consisting of paired positive-negative belts, occur in Canada at structural boundaries between geological provinces. The associated anomalous masses produce what are termed gravitationally induced stresses. These stresses may contribute to the failure of rocks along preexisting faults, or other zones of weakness. In the case of a typical structural boundary, failure at shallow depths in the crust is likely to occur in the region outlined by the negative gravity anomaly, whereas failure deeper within the crust and upper mantle may occur beneath the positive anomaly. Along the lower St. Lawrence valley, good spatial correlation is found between regions of high seismicity and those negative free-air anomaly areas which are adjacent to prominent free-air gravity highs. It is suggested that in a heavily faulted region, such as the lower St. Lawrence valley, gravitationally induced stresses may be a contributing factor to the production of earthquakes in regions which are otherwise already close to failure.

A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - Seismic and gravity data from afar in relation to surrounding areas

1970 ◽  
Vol 267 (1181) ◽  
pp. 339-358 ◽  
Keyword(s):  
Red Sea ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Seismic Energy ◽  
Free Air ◽  
Seismic Surface Waves ◽  
Free Air Gravity ◽  
Surrounding Areas ◽  
Tectonic Features ◽  
Afar Triangle

The Afar triangle is bordered, to the west, by a seismic belt running along and on top of the escarpment. Seventy-five percent of the seismic energy of the area is released along this belt. The epicentre distribution along the western escarpment coincides either with major north-south marginal tectonic features or with cross-rift faulting. A second epicentre lineation runs at N 15° E through central Afar. To the south-east, in the region of the Gulf of Tadjura, epicentre locations offer no distinct lineation. The sum of the free-air gravity anomalies over Afar is almost zero; Bouguer values are generally negative and strictly proportional to elevation. Absolute Bouguer positive values are found only over volcanic centres and along the northeastern coast; their maximum does not compare with the positive values found over the nearby Red Sea trough. Evidence based on attenuation and dispersion of seismic surface waves and on gravity profiles suggests a continental crustal structure of relatively ‘standard’ thickness under the Afar triangle.

scholarly journals Geoid Modelling of Kalimantan Island using Airborne Gravity Data and Global Geoid Model (EGM2008)

2021 ◽  
Vol 936 (1) ◽  
pp. 012029
Author(s):  
Zahroh Arsy Udama ◽  
Ira Mutiara Anjasmara ◽  
Arisauna Maulidyan Pahlevi ◽  
Anas Sharafeldin Mohamed Osman
Keyword(s):  
Standard Deviation ◽  
Gravity Anomaly ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Gravimetric Geoid ◽  
Wave Component ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Gravity ◽  
Local Geoid

Abstract The availability of geoids, especially in survey and mapping activities, is useful for transforming the geometric heights obtained from observations of the Global Navigation Satellite System (GNSS) into orthometric heights that have real physical meanings such as those obtained from waterpass measurements. If a geoid is available, the orthometric heights of points on earth can be determined using the GNSS heighting method. The use of modern survey and mapping instruments based on satellite observations such as GNSS is more efficient in terms of time, effort, and cost compared to the accurate waterpass method. According to the Indonesian Geospatial Information Agency (BIG) it is stated that the application of geoid as a national Vertical Geospatial Reference System has an adequate and ideal category if the accuracy is higher than 15 cm. Recent studies have shown that it is possible to generate local geoid models with centimetre accuracy by utilizing airborne gravity data. We calculate free-air gravity anomaly data is calculated by processing airborne gravity and GNSS data using the Stokes Integral method on AGR software. Next a geoid model is created by calculating the contribution of three components, namely the long wave component represented by the EGM2008 global geoid data model, the shortwave component represented by the Shuttle Radar Topography Mission (SRTM) data and the medium wave component represented by the free-air gravity anomaly data. The geoid model validation was carried out using the geoid fitting method for geoid accuracy by calculating the difference between the gravimetric geoid and the geometric geoid and comparing it with the global geoid model EGM2008 degrees 2190. As a result, the total geoid model accuracy value was determined to be 49.4 cm on gravimetric geoid undulations with a standard deviation of 7.1 cm. Meanwhile, the results of the EGM2008 geoid undulation accuracy test at 2190 degrees resulted in an accuracy of 51.9 cm with a standard deviation of 9.9 cm. These results indicate that the local geoid model from airborne gravity measurement data produces a geoid model with a higher accuracy than the global geoid model EGM2008 degrees 2190. However, the accuracy of the resulting data is still below the BIG standard of 15 cm, so further research is needed to produce a geoid model which conforms to the standard.

Crustal modeling from spectrally correlated free‐air and terrain gravity data—A case study of Ohio

Geophysics ◽  
2000 ◽  
Vol 65 (4) ◽  
pp. 1057-1069 ◽  
Author(s):  
Jeong Woo Kim ◽  
Ralph R. B. von Frese ◽  
Hyung Rae Kim
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Crustal Thickness ◽  
Earthquake Hazards ◽  
Spectral Correlation ◽  
Free Air ◽  
Correlation Spectrum ◽  
Gravity Effects ◽  
Thickness Variations ◽  
Free Air Gravity

We investigate the use of spectral correlation theory to analyze terrain gravity effects and free‐air gravity anomalies of Ohio for possible constraints on the thickness variations and neotectonics of the crust. Terrain gravity effects are computed from the topography by Gauss‐Legendre quadrature integration and are compared against independent free‐air gravity anomaly observations for their wavenumber correlation spectrum. Spectral correlation filters are designed accordingly to extract terrain‐correlated free‐air gravity anomalies that are subtracted from the terrain gravity effects for estimates of the compensated terrain gravity effects. These effects are used to model the Moho by inversion, assuming they predominantly reflect crustal thickness variations. Our results characterize the middle third of Ohio as a broad zone of thickened Precambrian crust, which also may include rifted regions where the thickness of the prerift crust has been reduced greatly. Furthermore, we find that about 83% of the instrumentally determined earthquake epicenters are located within the inferred thinner regions of Ohio’s crust or at their margins where compressional stresses may dominate. In general, these crustal thickness variations provide new constraints on modeling the tectonic evolution and geotechnical parameters of the crust—constraints that are important for evaluating earthquake hazards, the distribution and extraction of crustal resources, and the storage of hazardous waste and other crustal engineering applications.

Gravity data collection with a CG5 gravitymeter for densification of the gravity data around the AUT1 IHRF station

2021 ◽  
Author(s):  
Dimitrios A. Natsiopoulos ◽  
Elisavet G. Mamagiannou ◽  
Eleftherios A. Pitenis ◽  
Georgios S. Vergos ◽  
Ilias N. Tziavos ◽  
...  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Absolute Gravity ◽  
Dual Frequency ◽  
Height Determination ◽  
Free Air ◽  
Gravity Measurements ◽  
Gravity Database ◽  
Free Air Gravity ◽  
Geological Complexity

<p>Within the GeoGravGOCE project, funded by the Hellenic Foundation for Research Innovation, a main goal has been the densification of the available land gravity database around the eastern part of the city of Thessaloniki, Greece, where the core International Height Reference Frame (IHRF) station AUT1 is located in order to improve regional geoid and potential determination. Hence it was deemed necessary to densify the available gravity data within radiuses of 10 km, 20 km, 50 km and 100 km from the AUT1 core IHRF site. In that frame, and given the geological complexity of the region surrounding Thessaloniki and the significant variations of the terrain, gravity campaigns were appropriately designed and gravity measurements were carried out in order to densify the database and cover as much as possible traverses of varying altitude. The measurements have been carried out with the CG5 gravity meter of the GravLab group and dual-frequency GNSS receivers in RTK mode for orthometric height determination. In this  study we provide details of the gravity campaigns, the measurement principle and the finally derived gravity and free-air gravity anomalies. The mean measurement accuracy achieved was at the ~20 μGal level for the gravity measurements and ~3 cm for the orthometric heights. In all cases the final derived gravity value was based on the absolute point established by the GravLab team at the AUTH seismological station premises with the A10 (#027) absolute gravity meter.</p>

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