The unification of gravity data for Ireland-Northern Ireland

2020 ◽  
Vol 39 (2) ◽  
pp. 135-143
Author(s):  
Sajjad Sajjadi ◽  
Zdeněk Martinec ◽  
Patrick Prendergast ◽  
Jan Hagedoorn ◽  
Libor Šachl ◽  
...  
Keyword(s):  
Northern Ireland ◽  
Tide Gauge ◽  
Gravity Data ◽  
Base Station ◽  
Base Stations ◽  
Data Format ◽  
Free Air ◽  
Vertical Datum ◽  
Systematic Biases ◽  
Free Air Gravity

The systematic biases and errors associated with gravity data in Ireland and Northern Ireland and the conversion of gravity to a consistent and unified system are analyzed. The gravity data in Ireland and Northern Ireland are given in different coordinate systems (Irish Grid and Irish Transverse Mercator), different gravity base stations (Dunsink and Cambridge), and different vertical datums (Malin Head and Belfast tide gauge). The conversion of the gravity data to a consistent system, which refers to unified coordinates, base station, and vertical datum, is essential in geophysics and geodesy, especially in geoid determination. A new standardized and unified data format is computed and proposed for the supply of gravity data for Ireland and Northern Ireland to minimize the potential of misinterpreting the data. As part of this study, simple Bouguer and free-air gravity anomaly maps are produced for Ireland and Northern Ireland to give an example of how to integrate the data.

scholarly journals Inversion of IceBridge gravity data for continental shelf bathymetry beneath the Larsen Ice Shelf, Antarctica

2012 ◽  
Vol 58 (209) ◽  
pp. 540-552 ◽  
Author(s):  
James R. Cochran ◽  
Robin E. Bell
Keyword(s):  
Continental Shelf ◽  
Ocean Circulation ◽  
Gravity Data ◽  
Radar Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Free Air ◽  
Free Air Gravity ◽  
Larsen Ice Shelf ◽  
Possible Cause

AbstractA possible cause for accelerated thinning and break-up of floating marine ice shelves is warming of the water in the cavity below the ice shelf. Accurate bathymetry beneath large ice shelves is crucial for developing models of the ocean circulation in the sub-ice cavities. A grid of free-air gravity data over the floating Larsen C ice shelf collected during the IceBridge 2009 Antarctic campaign was utilized to develop the first bathymetry model of the underlying continental shelf. Independent control on the continental shelf geologic structures from marine surveys was used to constrain the inversion. Depths on the continental shelf beneath the ice shelf estimated from the inversion generally range from about 350 to 650 m, but vary from <300 to >1000 m. Localized overdeepenings, 20-30 km long and 900-1000 m deep, are located in inlets just seaward of the grounding line. Submarine valleys extending seaward from the overdeepenings coalesce into two broad troughs that extend to the seaward limit of the ice shelf and appear to extend to the edge of the continental shelf. The troughs are generally at a depth of 550-700 m although the southernmost mapped trough deepens to over 1000 m near the edge of the ice shelf just south of 68° S. The combination of the newly determined bathymetry with published ice-draft determinations based on laser altimetry and radar data defines the geometry of the water-filled cavity. These newly imaged troughs provide a conduit for water to traverse the continental shelf and interact with the overlying Larsen C ice shelf and the grounding lines of the outlet glaciers.

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

&lt;p&gt;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.&lt;/p&gt;

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.

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.

scholarly journals Airborne geoid mapping of land and sea areas of East Malaysia

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
H. Jamil ◽  
M. Kadir ◽  
R. Forsberg ◽  
A. Olesen ◽  
M. N. Isa ◽  
...  
Keyword(s):  
Spherical Harmonic ◽  
Tide Gauge ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Gravimetric Geoid ◽  
Spherical Harmonic Degree ◽  
Vertical Datum ◽  
East Malaysia ◽  
Marine Areas ◽  
Airborne Survey

AbstractThis paper describes the development of a new geoid-based vertical datum from airborne gravity data, by the Department of Survey and Mapping Malaysia, on land and in the South China Sea out of the coast of East Malaysia region, covering an area of about 610,000 square kilometres. More than 107,000 km flight line of airborne gravity data over land and marine areas of East Malaysia has been combined to provide a seamless land-to-sea gravity field coverage; with an estimated accuracy of better than 2.0 mGal. The iMAR-IMU processed gravity anomaly data has been used during a 2014-2016 airborne survey to extend a composite gravity solution across a number of minor gaps on selected lines, using a draping technique. The geoid computations were all done with the GRAVSOFT suite of programs from DTU-Space. EGM2008 augmented with GOCE spherical harmonic model has been used to spherical harmonic degree N = 720. The gravimetric geoid first was tied at one tide-gauge (in Kota Kinabalu, KK2019) to produce a fitted geoid, my_geoid2017_fit_kk. The fitted geoid was offset from the gravimetric geoid by +0.852 m, based on the comparison at the tide-gauge benchmark KK2019. Consequently, orthometric height at the six other tide gauge stations was computed from H

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.

A deterministic approach toward isostatic gravity residuals—A case study from South America

Geophysics ◽  
1996 ◽  
Vol 61 (4) ◽  
pp. 1022-1033 ◽  
Author(s):  
David A. Chapin
Keyword(s):  
South America ◽  
Gravity Data ◽  
Crustal Thickness ◽  
Crustal Thickening ◽  
Density Contrast ◽  
Data Sets ◽  
Topographic Effects ◽  
Continental Scale ◽  
Free Air ◽  
Free Air Gravity

A new deterministic method for correcting isostatic effects in gravity data sets overcomes the deficiencies of empirically based methods. This technique produces a superior gravity image for South America and has application to other continental‐scale gravity data sets. The basis for the correction is the Airy‐Heiskanen isostatic model, which assumes that surface topography is supported by crustal thickening. The three key parameters, (1) the crustal thickness at sea‐level, (2) the surface reduction density, and (3) the density contrast between the crust and the mantle, are determined directly from the elevation, free‐air gravity, and Bouguer gravity data sets. The surface density parameter of 2.60 g/cc is determined using a new fractal technique. This technique assumes that the topography is fractal. The best value for density is that which minimizes the fractal component caused by topographic effects. The new value is substantially different than the 2.67 g/cc density assumed by many previous workers for most continental‐scale data sets. The crust/mantle density contrast parameter of 0.45 g/cc is determined by comparison between the densities determined from crossplots of the Bouguer values versus elevation. The crustal thickness parameter of 30 km is determined using a spectral method applied to the free‐air gravity. The results of this work are not only an isostatic residual map, but a methodology that cross checks the data for quality control. The final isostatic residual map can be used with confidence for basin evaluation throughout the continent of South America. Basins at high elevations, like the eastern foreland basins of the Andes and the Altiplano Basin, are imaged better by using this method.

scholarly journals Seabed topography beneath Larsen C Ice Shelf from seismic soundings

2013 ◽  
Vol 7 (4) ◽  
pp. 4177-4206
Author(s):  
A. M. Brisbourne ◽  
A. M. Smith ◽  
E. C. King ◽  
K. W. Nicholls ◽  
P. R. Holland ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Ocean Circulation ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Gravity Inversion ◽  
Oceanic Circulation ◽  
Ice Shelf ◽  
Free Air ◽  
Cavity Thickness ◽  
Free Air Gravity

Abstract. Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general <10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-shelf ocean circulation models.

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.

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