scholarly journals Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

2021 ◽  
Author(s):  
Bart Root ◽  
Josef Sebera ◽  
Wolfgang Szwillus ◽  
Cedric Thieulot ◽  
Zdenek Martinec ◽  
...  
Keyword(s):  
Gravity Field ◽  
Spherical Harmonic ◽  
Short Wavelength ◽  
Field Data ◽  
The Other ◽  
Potential Fields ◽  
Spherical Harmonic Analysis ◽  
Constant Density ◽  
Forward Modelling ◽  
Density Interface

Abstract. Several alternative gravity forward modelling methodologies and associated numerical codes with their own advantages and limitations are available for the Solid Earth community. With the upcoming state-of-the-art lithosphere density models and accurate global gravity field data sets it is vital to understand the opportunities and limitations of the various approaches. In this paper, we discuss the four widely used techniques: global spherical harmonics (GSH), tesseroid integration (TESS), triangle integration (TRI), and hexahedral integration (HEX). A constant density shell benchmark shows that all four codes can produce similar precise gravitational potential fields. Two additional shell tests were conducted with more complicated density structures: lateral varying density structures and a Moho density interface between crust and mantle. The differences between the four codes were all below 1.5 percent of the modeled gravity signal suitable for reproducing satellite-acquired gravity data. TESS and GSH produced the most similar potential fields (< 0.3 percent). To examine the usability of the forward modelling codes for realistic geological structures, we use the global lithosphere model WINTERC-G, that was constrained, among other data, by satellite gravity field data computed using a spectral forward modeling approach. This spectral code was benchmarked against the GSH and it was confirmed that both approaches produce similar gravity solution with negligible differences between them. In the comparison of the different WINTERC-G-based gravity solutions, again GSH and TESS performed best. Only short-wavelength noise is present between the spectral and tesseroid forward modelling approaches, likely related to the different way in which the spherical harmonic analysis of the varying boundaries of the mass layer is performed. The Spherical harmonic basis functions produces small differences compared to the tesseroid elements especially at sharp interfaces, which introduces mostly short-wavelength differences. Nevertheless, both approaches (GSH and TESS) result in accurate solutions of the potential field with reasonable computational resources. Differences below 0.5 percent are obtained, resulting in residuals of 0.076 mGal standard deviation at 250 km height. The biggest issue for TRI is the characteristic pattern in the residuals that is related to the grid layout. Increasing the resolution and filtering allows for the removal of most of this erroneous pattern, but at the expense of higher computational loads with respect to the other codes. The other spatial forward modelling scheme HEX has more difficulty in reproducing similar gravity field solutions compared to GSH and TESS. These particular approaches need to go to higher resolutions, resulting in enormous computation efforts. The hexahedron-based code performs less than optimal in the forward modelling of the gravity signature, especially of a lateral varying density interface. Care must be taken with any forward modelling software as the approximation of the geometry of the WINTERC-G model may deteriorate the gravity field solution.

Interactive gravity inversion

Geophysics ◽  
2006 ◽  
Vol 71 (1) ◽  
pp. J1-J9 ◽  
Author(s):  
João B. C. Silva ◽  
Valéria C. F. Barbosa
Keyword(s):  
Gravity Field ◽  
Field Data ◽  
Synthetic Data ◽  
The Other ◽  
Density Contrast ◽  
Gravity Inversion ◽  
Homogeneous Body ◽  
New Approach ◽  
Line Segments ◽  
Gravity Fields

We have developed a new approach for estimating the location and geometry of several density anomalies that give rise to a complex, interfering gravity field. The user interactively defines the assumed outline of the true gravity sources in terms of points and line segments, and the method estimates sources closest to the specified outline to achieve a match between the predicted and observed gravity fields. Each gravity source is assumed to be a homogeneous body with a known density contrast; different density contrasts may be assigned to each source. Tests with synthetic data show that the method can be of use in estimating (1) multiple laterally adjacent and closely situated gravity sources, (2) single gravity sources consisting of several homogeneous compartments with different density contrasts, and (3) two gravity sources with different density contrasts of the same sign, one totally enclosed by the other. The method is also applied to three different sets of field data where the gravity sources belong to the same categories established in the tests with synthetic data. The method produces solutions consistent with the known geologic attributes of the gravity sources, illustrating its potential practicality.

Reformulation of Parker–Oldenburg's method for Earth's spherical approximation

2020 ◽  
Vol 222 (2) ◽  
pp. 1046-1073
Author(s):  
Wenjin Chen ◽  
Robert Tenzer
Keyword(s):  
Gravity Field ◽  
Large Scale ◽  
Gravity Data ◽  
Spherical Approximation ◽  
Gravity Gradient ◽  
Global Studies ◽  
Forward Modelling ◽  
Density Interface ◽  
And Inversion ◽  
Interface Geometry

SUMMARY Parker–Oldenburg's method is perhaps the most commonly used technique to estimate the depth of density interface from gravity data. To account for large density variations reported, for instance, at the Moho interface, between the ocean seawater density and marine sediments, or between sediments and the underlying bedrock, some authors extended this method for variable density models. Parker–Oldenburg's method is suitable for local studies, given that a functional relationship between gravity data and interface geometry is derived for Earth's planar approximation. The application of this method in (large-scale) regional, continental or global studies is, however, practically restricted by errors due to disregarding Earth's sphericity. Parker–Oldenburg's method was, therefore, reformulated also for Earth's spherical approximation, but assuming only a uniform density. The importance of taking into consideration density heterogeneities at the interface becomes even more relevant in the context of (large-scale) regional or global studies. To address this issue, we generalize Parker–Oldenburg's method (defined for a spherical coordinate system) for the depth of heterogeneous density interface. Furthermore, we extend our definitions for gravity gradient data of which use in geoscience applications increased considerably, especially after launching the Gravity field and steady-state Ocean Circulation Explorer (GOCE) gravity-gradiometry satellite mission. For completeness, we also provide expressions for potential. The study provides the most complete review of Parker–Oldenburg's method in planar and spherical cases defined for potential, gravity and gravity gradient, while incorporating either uniform or heterogeneous density model at the interface. To improve a numerical efficiency of gravimetric forward modelling and inversion, described in terms of spherical harmonics of Earth's gravity field and interface geometry, we use the fast Fourier transform technique for spherical harmonic analysis and synthesis. The (newly derived) functional models are tested numerically. Our results over a (large-scale) regional study area confirm that the consideration of a global integration and Earth's sphericty improves results of a gravimetric forward modelling and inversion.

MASCON versus spherical harmonic solutions to global monthly time varying gravity field

2020 ◽  
Author(s):  
Juraj Janák ◽  
Adam Novák ◽  
Barbora Korekáčová
Keyword(s):  
Gravity Field ◽  
Spherical Harmonic ◽  
Polar Region ◽  
Field Model ◽  
River Basins ◽  
Spherical Harmonic Analysis ◽  
Time Varying ◽  
Gravity Field Model ◽  
Gravity Field Models ◽  
Research Centres

&lt;p&gt;Satellite missions Gravity Field and Climate Experiment (GRACE) and its successor (GRACE-FO) plays very important role in nowadays research in geodesy, geophysics, hydrology, oceanography, glaciology and climatology. Various research centres adopted different procedures for processing the GRACE/GRACE-FO measurements in order to get the main final product &amp;#8211; the global monthly gravity field model. Until now there have been developed and published two fundamentally different approaches to this problem. The first is well-known approach of spherical harmonic analysis and the second is more recent and more direct approach called in literature MASCON (Mass Concentration). The purpose of this contribution is to compare existing MASCON global monthly gravity field models with the selected models based on spherical harmonic approach. Comparison is performed in selected river basins and also in selected polar region. Chosen river basins differ both in size and seasonal changes of continental water storage to cover more situations. Comparison of different filtered versions of spherical harmonic solutions (DDK1 &amp;#8211; DDK7) with MASCON solution is also performed in one of the analysed river basins. Differences are analysed and advantages and drawbacks of two approaches and of particular models are discussed.&lt;/p&gt;

scholarly journals TGF: A New MATLAB-based Software for Terrain-related Gravity Field Calculations

2020 ◽  
Vol 12 (7) ◽  
pp. 1063
Author(s):  
Meng Yang ◽  
Christian Hirt ◽  
Roland Pail
Keyword(s):  
Density Distribution ◽  
Gravity Field ◽  
Mass Density ◽  
Computation Time ◽  
Spherical Approximation ◽  
Constant Density ◽  
Forward Modelling ◽  
Gravity Effects ◽  
Residual Terrain Modelling ◽  
Elevation Model

With knowledge of geometry and density-distribution of topography, the residual terrain modelling (RTM) technique has been broadly applied in geodesy and geophysics for the determination of the high-frequency gravity field signals. Depending on the size of investigation areas, challenges in computational efficiency are encountered when using an ultra-high-resolution digital elevation model (DEM) in the Newtonian integration. For efficient and accurate gravity forward modelling in the spatial domain, we developed a new MATLAB-based program called, terrain gravity field (TGF). Our new software is capable of calculating the gravity field generated by an arbitrary topographic mass-density distribution. Depending on the attenuation character of gravity field with distance, the adaptive algorithm divides the integration masses into four zones, and adaptively combines four types of geometries (i.e., polyhedron, prism, tesseroid and point-mass) and DEMs with different spatial resolutions. Compared to some publicly available algorithms depending on one type of geometric approximation, this enables accurate modelling of gravity field and greatly reduces the computation time. Besides, the TGF software allows to calculate ten independent gravity field functionals, supports two types of density inputs (constant density value and digital density map), and considers the curvature of the Earth by involving spherical approximation and ellipsoidal approximation. Further to this, the TGF software is also capable of delivering the gravity field of full-scale topographic gravity field implied by masses between the Earth’s surface and mean sea level. In this contribution, the TGF software is introduced to the geoscience community and its capabilities are explained. Results from internal and external numerical validation experiments of TGF confirmed its accuracy at the sub-mGal level. Based on TGF, the trade-off between accuracy and efficiency, values for the spatial resolution and extension of topography models are recommended. The TGF software has been extensively tested and recently been applied in the SRTM2gravity project to convert the global 3” SRTM topography to implied gravity effects at 28 billion computation points. This confirms the capability of TGF for dealing with large datasets. Together with this paper, the TGF software will be released in the public domain for free use in geodetic and geophysical forward modelling computations.

scholarly journals General Environment Description Language

2021 ◽  
Vol 11 (2) ◽  
pp. 740
Author(s):  
Krzysztof Zatwarnicki ◽  
Waldemar Pokuta ◽  
Anna Bryniarska ◽  
Anna Zatwarnicka ◽  
Andrzej Metelski ◽  
...  
Keyword(s):  
Intelligent Systems ◽  
General Purpose ◽  
The Other ◽  
Potential Fields ◽  
General Intelligence ◽  
Language Usage ◽  
Description Language ◽  
It Systems ◽  
New Research ◽  
Future Work

Artificial intelligence has been developed since the beginning of IT systems. Today there are many AI techniques that are successfully applied. Most of the AI field is, however, concerned with the so-called “narrow AI” demonstrating intelligence only in specialized areas. There is a need to work on general AI solutions that would constitute a framework enabling the integration of already developed narrow solutions and contribute to solving general problems. In this work, we present a new language that potentially can become a base for building intelligent systems of general purpose in the future. This language is called the General Environment Description Language (GEDL). We present the motivation for our research based on the other works in the field. Furthermore, there is an overall description of the idea and basic definitions of elements of the language. We also present an example of the GEDL language usage in the JSON notation. The example shows how to store the knowledge and define the problem to be solved, and the solution to the problem itself. In the end, we present potential fields of application and future work. This article is an introduction to new research in the field of Artificial General Intelligence.

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