Journal articles on the topic 'Gravity field anomalies'
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1
Apeh, O. I., E. C. Moka, and V. N. Uzodinma. "Evaluation of Gravity Data Derived from Global Gravity Field Models Using Terrestrial Gravity Data in Enugu State, Nigeria." Journal of Geodetic Science 8, no. 1 (December 1, 2018): 145–53. http://dx.doi.org/10.1515/jogs-2018-0015.
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Abstract Spherical harmonic expansion is a commonly applied mathematical representation of the earth’s gravity field. This representation is implied by the potential coeffcients determined by using elements/parameters of the field observed on the surface of the earth and/or in space outside the earth in the spherical harmonic expansion of the field. International Centre for Gravity Earth Models (ICGEM) publishes, from time to time, Global Gravity Field Models (GGMs) that have been developed. These GGMs need evaluation with terrestrial data of different locations to ascertain their accuracy for application in those locations. In this study, Bouguer gravity anomalies derived from a total of eleven (11) recent GGMs, using sixty sample points, were evaluated by means of Root-Mean-Square difference and correlation coeficient. The Root-Mean-Square differences of the computed Bouguer anomalies from ICGEMwebsite compared to their positionally corresponding terrestrial Bouguer anomalies range from 9.530mgal to 37.113mgal. Additionally, the correlation coe_cients of the structure of the signal of the terrestrial and GGM-derived Bouguer anomalies range from 0.480 to 0.879. It was observed that GECO derived Bouguer gravity anomalies have the best signal structure relationship with the terrestrial data than the other ten GGMs. We also discovered that EIGEN-6C4 and GECO derived Bouguer anomalies have enormous potential to be used as supplements to the terrestrial Bouguer anomalies for Enugu State, Nigeria.
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Inzhevatov, Ivan A. "DETERMINATION OF THE VERTICAL GRADIENT OF GRAVITY FROM GRAVITY ANOMALIES." Interexpo GEO-Siberia 6 (May 21, 2021): 116–24. http://dx.doi.org/10.33764/2618-981x-2021-6-116-124.
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In connection with the need to use the vertical gradient in the processing of the results of gravimetric measurements and their interpretation when solving problems of geology, geophysics, geodesy, geodynamics and navigation, in addition to the urgent problems of improvement, socalled indirect methods of measuring the vertical gradient, there is an equally urgent task of developing methods for determining the vertical gradient of gravity, using dependencies between different physical fields. The article presents the development and study of a method for determining the vertical gradient from gravity anomalies using the relationship between gravity anomalies and altitude based on field data obtained in the area of the Tashtagol field on Mount Boulanger in 2019 and 2020.
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Foroughi, Ismael, Abdolreza Safari, Pavel Novák, and Marcelo Santos. "Application of Radial Basis Functions for Height Datum Unification." Geosciences 8, no. 10 (October 2, 2018): 369. http://dx.doi.org/10.3390/geosciences8100369.
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Local gravity field modelling demands high-quality gravity data as well as an appropriate mathematical model. Particularly in coastal areas, there may be different types of gravity observations available, for instance, terrestrial, aerial, marine gravity, and satellite altimetry data. Thus, it is important to develop a proper tool to merge the different data types for local gravity field modelling and determination of the geoid. In this study, radial basis functions, as a commonly useful tool for gravity data integration, are employed to model the gravity potential field of the southern part of Iran using terrestrial gravity anomalies, gravity anomalies derived from re-tracked satellite altimetry, marine gravity anomalies, and gravity anomalies synthesized from an Earth gravity model. Reference GNSS/levelling (geometric) geoidal heights are used to evaluate the accuracy of the estimated local gravity field model. The gravimetric geoidal heights are in acceptable agreement with the geometric ones in terms of the standard deviation and the mean value which are 4.1 and 12 cm, respectively. Besides, the reference benchmark of the national first-order levelling network of Iran is located in the study area. The derived gravity model was used to compute the gravity potential difference at this point and then transformed into a height difference which results in the value of the shift of this benchmark with respect to the geoid. The estimated shift shows a good agreement with previously published studies.
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Ganagina, I. G., V. F. Kanushin, D. N. Goldobin, and I. V. Zverev. "Analysis of data on pure and mixed gravity anomalies obtained from the results of the space gravity missions GRACE, GOCE." Interexpo GEO-Siberia 1 (May 18, 2022): 130–37. http://dx.doi.org/10.33764/2618-981x-2022-1-130-137.
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The article analyzes the data of pure and mixed gravity anomalies on the territory of the Novosibirsk region, obtained from the results of the space gravimetric missions GRACE, GOCE. Gravimetric and geodetic measurements carried out in the study area made it possible to obtain mixed and simulate pure gravity anomalies. The information obtained was the starting point for the analysis of gravity anomalies calculated from the coefficients of the global geopotential models XGM2019e_2159, GOCO01S. The results of the study led to the conclusion that when calculating mixed gravity anomalies according to the combined geopotential model XGM2019e_2159 and pure gravity anomalies according to the GOCO01S satellite model data, equal root-mean-square errors were obtained (for mixed anomalies - 3.45 mGal, for pure - 3.44 mGal). Therefore, modern combined global gravity field models can be used to obtain pure anomalies on the earth's surface.
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Wan, Xiaoyun, Shuanggen Jin, Bo Liu, Song Tian, Weiya Kong, and Richard Fiifi Annan. "Effects of Interferometric Radar Altimeter Errors on Marine Gravity Field Inversion." Sensors 20, no. 9 (April 27, 2020): 2465. http://dx.doi.org/10.3390/s20092465.
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The traditional altimetry satellite, which is based on pulse-limited radar altimeter, only measures ocean surface heights along tracks; hence, leads to poorer accuracy in the east component of the vertical deflections compared to the north component, which in turn limits the final accuracy of the marine gravity field inversion. Wide-swath altimetry using radar interferometry can measure ocean surface heights in two dimensions and, thus, can be used to compute vertical deflections in an arbitrary direction with the same accuracy. This paper aims to investigate the impact of Interferometric Radar Altimeter (InRA) errors on gravity field inversion. The error propagation between gravity anomalies and InRA measurements is analyzed, and formulas of their relationship are given. By giving a group of possible InRA parameters, numerical simulations are conducted to analyze the accuracy of gravity anomaly inversion. The results show that the accuracy of the gravity anomalies is mainly influenced by the phase errors of InRA; and the errors of gravity anomalies have a linear approximation relationship with the phase errors. The results also show that the east component of the vertical deflections has almost the same accuracy as the north component.
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Singh, Bijendra. "Simultaneous computation of gravity and magnetic anomalies resulting from a 2‐D object." GEOPHYSICS 67, no. 3 (May 2002): 801–6. http://dx.doi.org/10.1190/1.1484524.
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This paper presents a new algorithm for the simultaneous computation of gravity and magnetic anomalies resulting from an infinitely long (2‐D) body with an arbitrary polygonal cross‐section. With the assumption of uniform volume density and magnetization, the gravity or magnetic field may be expressed as the field resulting from an equivalent distribution of surface mass density or surface pole density, respectively, over the surface of the source body. The resulting surface integrals are reduced to new line integrals using Stokes' theorem. The components of the fields for each bounding surface are expressed in terms of a new line integral and the solid angle subtended by the surface at the point of observation. Since these analytical solutions are similar in form, a direct relation is derived between gravity and magnetic fields, which allows their simultaneous computation. Hence, the same computer program can be used to compute the gravity field, the magnetic field, or both fields simultaneously. This new approach will find wide applications in the joint inversion of potential field data, as it will make the numerical computations much faster.
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REBOUÇAS, M. J., and A. F. F. TEIXEIRA. "CAUSAL ANOMALIES IN KALUZA–KLEIN GRAVITY THEORIES." International Journal of Modern Physics A 13, no. 18 (July 20, 1998): 3181–91. http://dx.doi.org/10.1142/s0217751x98001578.
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Causal anomalies in two Kaluza–Klein gravity theories are examined, particularly as to whether these theories permit solutions in which the causality principle is violated. It is found that similarly to general relativity the field equations of the space–time–mass Kaluza–Klein (STM-KK) gravity theory do not exclude violation of causality of Gödel type, whereas the induced matter Kaluza–Klein (IM-KK) gravity rules out noncausal Gödel-type models. The induced matter version of general relativity is shown to be an efficient therapy for causal anomalies that occurs in a wide class of noncausal geometries. Perfect fluid and dust Gödel-type solutions of the STM-KK field equations are studied. It is shown that every Gödel-type perfect fluid solution is isometric to the unique dust solution of the STM-KK field equations. The question as to whether 5D Gödel-type noncausal geometries induce any physically acceptable 4D energy–momentum tensor is also addressed.
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Piskarev, Alexey L., and Mikhail Yu Tchernyshev. "Magnetic and gravity anomaly patterns related to hydrocarbon fields in northern West Siberia." GEOPHYSICS 62, no. 3 (May 1997): 831–41. http://dx.doi.org/10.1190/1.1444192.
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A study of the features of gravity and magnetic fields in the vicinity of oil and gas reservoirs in West Siberia demonstrated a spatial relationship with the hydrocarbon deposits. The relevant magnetic and gravity anomalies cover approximately [Formula: see text] in northern West Siberia. Amplitude and frequency were investigated initially using double Fourier spectrum (DFS) analysis. This was followed by (1) application of transformations, filtering, and “moving windows” analysis; (2) compilation of maps of regional and local anomalies, and potential field derivatives; and (3) investigation of the distribution of parameters in areas of known deposits. Hydrocarbon deposits are located mostly at the slopes of positive regional gravity and magnetic anomalies which are interpreted as relating to deep riftogenic structures. At the same time, it is established that the location of hydrocarbon depositions coincides commonly with local gravity and magnetic minima generated by lows in basement density and magnetization. All known hydrocarbon deposits in northern West Siberia are in areas characterized by comparatively high gradients of constituent of gravity anomalies with a wavelength of about 90–100 km. These newly revealed links between reservoirs and potential field parameters may be a means to predict new discoveries in poorly explored territories and seas, primarily in Russia's Arctic shelf.
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Cilek, Mehmet Bora. "Redefining Gravity: Field versus Flow." Applied Physics Research 9, no. 2 (April 1, 2017): 87. http://dx.doi.org/10.5539/apr.v9n2p87.
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General Theory of Relativity constitutes the framework for our understanding of the universe, with an emphasis on gravity. Many of Einstein’s predictions have been verified experimentally but General and Special Theories of Relativity contain several anomalies and paradoxes, yet to be answered. Also, there are serious conflicts with Quantum Mechanics; gravity being the weakest and least understood force, is a major problem.Supported by clear experimental evidence, it is theorised that gravity is not a field or spacetime curvature effect, but rather has a flow mechanism. This is not an alternative theory of gravity with an alternative metric. Established laws and equations from Newton and Einstein are essentially left unchanged. However, spacetime curvature is replaced with flow, producing a refined and compatible theory.
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Shtogryn, M. V., S. G. Anikeyev, and O. O. Synytska. "COMPLEX GEOPHYSICAL STUDIES OF THE IVANO-FRANKIVSK NATIONAL TECHNICAL UNIVERSITY OF OIL AND GAS TERRITORY." Oil and Gas Power Engineering, no. 1(31) (June 26, 2019): 7–17. http://dx.doi.org/10.31471/1993-9868-2019-1(31)-7-17.
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The results of high-precision integrated geophysical studies of the Ivano-Frankivsk National University territory are presented. Research methods used are electrical prospecting and gravity and magnetic prospecting. According to the results of geodetic measurements and field geophysical observations, heights maps of the territory, regional components and detailed maps of local anomalies of the gravitational and magnetic fields, and also, according to the data of vertical electrical sounding, geoelectric sections along interpretation profiles were constructed. For the construction data on the geological and tectonic structure of the section to the depths of the first hundred meters were used, as well as geophysical materials obtained in previous years through of the Ivano-Frankivsk city territory. The analysis of the general behavior of the regional components of the gravimagnetic fields and morphology of geophysical anomalies was performed. The geological interpretation of the identified individual local gravitational and magnetic anomalies is presented. A regional field of gravity tends to increase in the direction of increasing heights in the study area and the regional magnetic field has an insignificant, but inverse relationship. A series of positive small intensity local anomalies of the field of gravity is probably due to the rocks of the Kosovska and Tyraska suite, for example, compacted carbonates or anhydrites. Local magnetic anomalies have a relatively small intensity ranging from -100 nTl to 500 nTl and due mainly to university facilities and communications. According to the results of the analysis of the intensity of geophysical fields, a general forecast estimate of the ecological state of the research area is presented. The obtained field intensity values are much lower than the sanitary norms.
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Chornaya, O. A., and T. P. Yegorova. "Gravity field of Sarmatia according to satellite data (model EIGEN-6S2) and its interpretation." Geofizicheskiy Zhurnal 43, no. 3 (July 28, 2021): 47–63. http://dx.doi.org/10.24028/gzh.v43i3.236380.
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The paper presents a brief overview of satellite observations of the CHAMP, GRACE and GOCE missions to study the Earth’s global gravity field, and the used mathematical apparatus in the form of an expansion of the geopotential in spherical harmonics. The application of satellite data in various fields of Earth Sciences is considered. As a basic global model of the Earth’s gravity field based on satellite data we used the EIGEN-6S2 model [Rudenko et al, 2014] that combines satellite mission data GRACE and GOCE, and also uses satellite data of LAGEOUS laser ranging. On its basis, the gravity field of Sarmatia was analyzed using the Free Air anomalies, Bouguer anomalies, the second radial derivative of the geopotential and the geoid heights. The geological units of Sarmatia and its surroundings are most clearly manifested in the Free Air anomalies and in the distribution of the second derivative of the geopotential, showing differences in the gravity field pattern of the Ukrainian Shield, the Voronezh Massif, and the Pripyat-Dnieper-Donets basin (PDDB) with characteristic anomalies of the general northwest strike. The continuation of the PDDB in a southeastern direction through the Karpinsky Swell to the northern part of the Caspian Sea confirms the existence of an extended ancient tectonic zone of the Sarmato-Turanian lineament. The geoid within Sarmatia shows in general a regional west-east gradient change from +40 m in the west to -10 m in the east. Such large-scale geoid changes are determined by the Sarmatia position between two global geoid anomalies — the maximum of the North Atlantic and the minimum of the Indian Ocean.
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FOROUGHI, Ismael, Yosra AFRASTEH, Sabah RAMOUZ, and Abdolreza SAFARI. "LOCAL EVALUATION OF EARTH GRAVITATIONAL MODELS, CASE STUDY: IRAN." Geodesy and cartography 43, no. 1 (March 27, 2017): 1–13. http://dx.doi.org/10.3846/20296991.2017.1299839.
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Global gravity models are being developed according to new data sets available from satellite gravity missions and terrestrial/marine gravity data which are provided by different countries. Some countries do not provide all their available data and the global gravity models have many vague computational methods. Therefore, the models need to be evaluated locally before using. It is generally understood that the accuracy of global gravity models is enough for local (civil, mining, construction, etc.) projects, however, our results in Iran show that the differences between synthesized values and observation data reach up to ∼300 mGal for gravity anomalies and ∼2 m for geoid heights. Even by applying the residual topographical correction to synthetized gravity anomalies, the differences are still notable. The accuracy of global gravity models for predicting marine gravity anomalies is also investigated in Persian Gulf and the results show differences of ∼140 mGal in coastal areas. The results of evaluating selected global gravity models in Iran indicate that the EIGEN-6C4 achieves the lowest RMS for estimating the geoid heights. EGM08 predicts the closest results to terrestrial gravity anomalies. DIR-R5 GOCE satellite-only model estimates the low-frequency part of gravity field more accurately. The best prediction of marine gravity anomalies is also achieved by EGM08.
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Holstein, Horst. "Gravimagnetic similarity in anomaly formulas for uniform polyhedra." GEOPHYSICS 67, no. 4 (July 2002): 1126–33. http://dx.doi.org/10.1190/1.1500373.
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Gravitational and magnetic anomalies of an arbitrary target body are linked through Poisson's differential relation. For a uniform polyhedral target, Poisson's relation reduces to an algebraic link between gravity and magnetic anomaly formulas. The derivation is given in tensor form. It identifies for each target facet edge a vector function, in terms of which the gravitational and magnetic potential and field anomaly formulas are similarly expressed as appropriately weighted linear combinations. This similarity unifies the theory of uniform polyhedral anomalies. It benefits analysis and construction of software that naturally embraces all anomalies in a single code. The analysis is exemplified by a discussion of singularities and by the adaptation of three gravity‐field algorithms to the remaining gravitational and magnetic cases, while retaining the respective computational advantages of the former gravity‐field algorithms.
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Mahbuby, Hany, Yazdan Amerian, Amirhossein Nikoofard, and Mehdi Eshagh. "Application of the nonlinear optimisation in regional gravity field modelling using spherical radial base functions." Studia Geophysica et Geodaetica 65, no. 3-4 (October 2021): 261–90. http://dx.doi.org/10.1007/s11200-020-1077-y.
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AbstractThe gravity field is a signature of the mass distribution and interior structure of the Earth, in addition to all its geodetic applications especially geoid determination and vertical datum unification. Determination of a regional gravity field model is an important subject and needs to be investigated and developed. Here, the spherical radial basis functions (SBFs) are applied in two scenarios for this purpose: interpolating the gravity anomalies and solving the fundamental equation of physical geodesy for geoid or disturbing potential determination, which has the possibility of being verified by the Global Navigation Satellite Systems (GNSS)/levelling data. Proper selections of the number of SBFs and optimal location of the applied SBFs are important factors to increase the accuracy of estimation. In this study, the gravity anomaly interpolation based on the SBFs is performed by Gauss-Newton optimisation with truncated singular value decomposition, and a Quasi-Newton method based on line search to solve the minimisation problems with a small number of iterations is developed. In order to solve the fundamental equation of physical geodesy by the SBFs, the truncated Newton optimisation is applied as the Hessian matrix of the objective function is not always positive definite. These two scenarios are applied on the terrestrial free-air gravity anomalies over the topographically rough area of Auvergne. The obtained accuracy for the interpolated gravity anomaly model is 1.7 mGal with the number of point-masses about 30% of the number of observations, and 1.5 mGal in the second scenario where the number of used kernels is also 30%. These accuracies are root mean square errors (RMSE) of the differences between predicted and observed gravity anomalies at check points. Moreover, utilising the optimal constructed model from the second scenario, the RMSE of 9 cm is achieved for the differences between the gravimetric height anomalies derived from the model and the geometric height anomalies from GNSS/levelling points.
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Nyoka, Chivatsi Jonathan, Ami Hassan Md Din, and Muhammad Faiz Pa’suya. "COMPUTATION OF GRAVITY FIELD FUNCTIONALS WITH A LOCALIZED LEVEL ELLIPSOID." Journal of Information System and Technology Management 6, no. 24 (December 1, 2021): 226–42. http://dx.doi.org/10.35631/jistm.624022.
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The description of the earth’s gravity field is usually expressed in terms of spherical harmonic coefficients, derived from global geopotential models. These coefficients may be used to evaluate such quantities as geoid undulations, gravity anomalies, gravity disturbances, deflection of the vertical, etc. To accomplish this, a global reference normal ellipsoid, such as WGS84 and GRS80, is required to provide the computing reference surface. These global ellipsoids, however, may not always provide the best fit of the local geoid and may provide results that are aliased. In this study, a regional or localized geocentric level ellipsoid is used alongside the EGM2008 to compute gravity field functionals in the state of Johor. Residual gravity field quantities are then computed using GNSS-levelled and raw gravity data, and the results are compared with both the WGS84 and the GRS80 equipotential surfaces. It is demonstrated that regional level ellipsoids may be used to compute gravity field functionals with a better fit, provided the zero-degree spherical harmonic is considered. The resulting residual quantities are smaller when compared with those obtained with global ellipsoids. It is expected that when the remove-compute-restore method is employed with such residuals, the numerical quadrature of the Stoke’s integral may be evaluated on reduced gravity anomalies that are smoother compared to when global equipotential surfaces are used
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Pedersen, Laust B., and Mehrdad Bastani. "Estimating rock-vector magnetization from coincident measurements of magnetic field and gravity gradient tensor." GEOPHYSICS 81, no. 3 (May 2016): B55—B64. http://dx.doi.org/10.1190/geo2015-0100.1.
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Poisson’s theorem relating components of the magnetic field to components of the gradient of the gravity vector assuming a common source has been cast into a general form. A given magnetization distribution in the terrain or in the underlying crust is propagated into the corresponding magnetic field through the gravity gradient tensor. Conversely, measured magnetic field anomalies and measured gravity gradient tensor anomalies can be used to estimate the unknown magnetization vectors without knowledge of the geometry of the sources. We have tested the method on recently acquired data over a greenstone belt in Northern Sweden. The topographic relief was sufficiently variable to dominate the measured gravity gradient tensor. In practice, we have concentrated on areas where the norm of the gravity gradient tensor reached a maximum so that there was a better chance of identifying isolated sources with well-defined density and magnetization. We have surrounded the selected points by a small window and used all the data lying within that window to estimate the magnetization vectors. We have compared the estimated amplitudes and directions of magnetization with those measured from selected rock samples in the area and found a relatively modest agreement. We have interpreted this as a result of two effects: (1) Measured magnetizations are generally lower than those estimated by this method, and we believe that this is related to the fact that the collection of samples in the field is biased because of a small number of outcrops in most parts of the area. (2) This analysis is biased toward high-amplitude magnetic anomalies; i.e., the estimation procedure works best for high-amplitude magnetic anomalies, in which case, the influence of neighboring anomalies is reduced. The estimated magnetization directions show a strong dominance of remanent magnetization over induced magnetization in agreement with laboratory measurements on rock samples from the area.
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Godah, Walyeldeen, Malgorzata Szelachowska, and Jan Krynski. "Accuracy assessment of GOCE-based geopotential models and their use for modelling the gravimetric quasigeoid - A case study for Poland." Geodesy and Cartography 63, no. 1 (June 1, 2014): 3–24. http://dx.doi.org/10.2478/geocart-2014-0001.
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Abstract The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) has significantly upgraded the knowledge on the Earth gravity field. In this contribution the accuracy of height anomalies determined from Global Geopotential Models (GGMs) based on approximately 27 months GOCE satellite gravity gradiometry (SGG) data have been assessed over Poland using three sets of precise GNSS/levelling data. The fits of height anomalies obtained from 4th release GOCE-based GGMs to GNSS/levelling data were discussed and compared with the respective ones of 3rd release GOCE-based GGMs and the EGM08. Furthermore, two highly accurate gravimetric quasigeoid models were developed over the area of Poland using high resolution Faye gravity anomalies. In the first, the GOCE-based GGM was used as a reference geopotential model, and in the second - the EGM08. They were evaluated with GNSS/levelling data and their accuracy performance was assessed. The use of GOCE-based GGMs for recovering the long-wavelength gravity signal in gravimetric quasigeoid modelling was discussed.
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Arkani‐Hamed, J., and W. E. S. Urquhart. "Reduction to the pole of the North American magnetic anomalies." GEOPHYSICS 55, no. 2 (February 1990): 218–25. http://dx.doi.org/10.1190/1.1442829.
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Magnetic anomalies of North America are reduced to the pole using a generalized technique which takes into account the variations in the directions of the core field and the magnetization of the crust over North America. The reduced‐to‐the‐pole magnetic anomalies show good correlations with a number of regional tectonic features, such as the Mid‐Continental rift and the collision zones along plate boundaries, which are also apparent in the vertical gravity gradient map of North America. The magnetic anomalies do not, however, show consistent correlation with the vertical gravity gradients, suggesting that magnetic and gravity anomalies do not necessarily arise from common sources.
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Bell, Robin E., Bernard J. Coakley, and Robert W. Stemp. "Airborne gravimetry from a small twin engine aircraft over the Long Island Sound." GEOPHYSICS 56, no. 9 (September 1991): 1486–93. http://dx.doi.org/10.1190/1.1443170.
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In January 1990, a test of the feasibility of airborne gravimetry from a small geophysical survey aircraft, a Cessna 404, was conducted over the Long Island Sound using a Bell Aerospace BGM-3 sea gravity meter. Gravity has been measured from large aircraft and specially modified de Havilland Twin Otters but never from small, standard survey aircraft. The gravity field of the Long Island Sound is dominated by an asymmetric positive 30 mGal anomaly which is well constrained by both marine and land gravity measurements. Using a Trimble 4000 GPS receiver to record the aircraft’s horizontal position and radar altimeter elevations to recover the vertical accelerations, gravity anomalies along a total of 65 km were successfully measured. The root mean square (rms) difference between the airborne results and marine measurements within 2 km of the flight path was 2.6 mGal for 15 measured values. The anomalies recovered from airborne gravimetry can also be compared with the gridded regional free air gravity field calculated using all available marine and land gravity measurements. The rms difference between 458 airborne gravity measurements and the regional gravity field is 2.7 mGal. This preliminary experiment demonstrates that gravity anomalies, with wavelengths as short as 5 km, can be measured from small aircraft with accuracies of 2.7 mGal or better. The gravity measurements could be improved by higher quality vertical and horizontal positioning and tuning the gravimeter’s stabilized platform for aircraft use.
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Tian, Yu, Huiyou He, Qing Ye, and Yong Wang. "Method for assessing the three-dimensional density structure based on gravity gradient inversion and gravity gradient curvature." Journal of Geophysics and Engineering 19, no. 5 (September 19, 2022): 1064–81. http://dx.doi.org/10.1093/jge/gxac071.
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Abstract Compared with gravity data, gravity gradient data can reflect the structural features of density anomalies with higher sensitivity and resolution. Gravity gradient inversion is a common method for interpreting gravity gradient data, but the non-uniqueness of gravity gradient inversion solutions makes it difficult to quickly determine the effectiveness and reliability of the inversion results. To solve this problem, this paper combines the gravity gradient inversion and gravity gradient curvature methods and applies them to different sets of synthetic models. The gravity gradient inversion results are useful primarily for determining the spatial distributions and physical properties of density anomalies, while the gravity gradient curvature results have a prominent advantage in judging the geometric features of the density anomalies. In addition, one form of gravity gradient curvature, the contour lines of the shape index, can be compared with the top view of the inversion results to rapidly confirm the distribution of density anomalies, which is especially valuable for unexplored regions. On the basis of the respective advantages and features of these two methods, the gravity gradient curvature can be used as an important criterion to judge the results of gravity gradient inversion. The two methods are then combined to analyse airborne gravity gradient data measured in the field at the Kauring Test Site in Australia. Compared with the findings of previous gravity inversion research, this study shows that several anomalous blocks exist in the vicinity of the central anomalies, thereby demonstrating that the combination of these two methods is effective and reliable in identifying density anomalies.
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Liu, Bei, Shaofeng Bian, Bing Ji, Shuguang Wu, Pengfei Xian, Cheng Chen, and Ruichen Zhang. "Application of the Fourier Series Expansion Method for the Inversion of Gravity Gradients using Gravity Anomalies." Remote Sensing 15, no. 1 (December 31, 2022): 230. http://dx.doi.org/10.3390/rs15010230.
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Accurate and highly precise gravity gradient data are an important component of, for example, gravity field modeling, seabed topography inversion, and resource exploration. However, high-precision gravity gradient data are difficult to obtain. To address this difficulty, this work introduces the Fourier series expansion method to the modeling of gravity gradient fields. Based on gravity anomalies, the analytic expressions of the gravity gradient tensors have been deduced, which provides a new mathematical method for obtaining gravity gradient data. The expression’s derivation and verification processes are as follows. First, these analytic expressions for inverting the gravity gradient based on gravity anomaly data are derived according to the Laplace equation, the boundary value conditions of spherical approximation, and the Fourier series expansion method. Then, global 1’ × 1’ gravity field data provided by UCSD are used to verify the accuracy of these formulas. Finally, the results are analyzed. The experimental results show that the results obtained based on this inversion formula can sufficiently show the details of gravity gradient changes. The formulas derived in this paper have good computational efficiency in the inversion of regional gravity gradients and provide a new mathematical method for gravity gradient data acquisition.
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Wang, Yang, Jun Li, Xuben Wang, and Xingxiang Jian. "Inversion Technique of Physical Parameters Based on Regularization Extension Depth Constraint." Earth Sciences Research Journal 23, no. 4 (October 1, 2019): 331–38. http://dx.doi.org/10.15446/esrj.v23n4.84340.
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Through the regularization downward continuation of gravity and magnetic anomalies, the depth of the field source can be solved. However, due to the Gibbs effect, the horizontal resolving power of the field source is poor. In view of this, based on the depth of field source established by regularization downward continuation, this paper proposes a physical property parameter inversion method based on iterative continuation and anomaly separation, which can effectively improve the inversion accuracy of superimposed anomaly physical parameters, and provide a new idea for solving the physical parameters of superposition gravity and magnetic anomalies.
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Petrova, A. A., and O. V. Latysheva. "THE STRUCTURE OF AQUIFERS BY MAGNETIC FIELD AND GRAVITY ANOMALIES." BULLETIN OF KAMCHATKA REGIONAL ASSOCIATION «EDUCATIONAL-SCIENTIFIC CENTER». EARTH SCIENCES. 2, no. 54 (2022): 32–49. http://dx.doi.org/10.31431/1816-5524-2022-2-54-32-49.
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The results of the study of the main characteristics and structural features of the aquifer systems of cold and thermal waters on the example of well-known sources in the Middle East are presented. The study of groundwater aquifers was carried out on the basis of the technology of geophysical data complex interpretation, taking into account the features of the aquifers geological structure. Aquifers and underground reservoirs are visualized as zones of reduced magnetization and density of rocks on deep petrophysical sections calculated from magnetic field and gravity anomalies. Horizontal subterranean water conduits can be clearly traced on the areal distributions of magnetization and density along the stretches of the lineaments with reduced values. Vertical subterranean water conduits stand out vividly on magnetic and density sections in the form of ascending tracks. As a result of the study of deep sections through the zones of known thermal springs, an estimate of the dependence of the source temperature on the depth of the feeding underground reservoirs was obtained. The article examines the potential of underground resources aquifers of the arid territories of Israel, the Kingdom of Saudi Arabia and the United Arab Emirates, for which the relevance of the water problem, apparently, will not decrease in the coming decades. The forecast of the location of groundwater karst reservoirs can be carried out by magnetic and density sections, taking into account two-dimensional models of the distribution of magnetization and density of rocks. The methodology of the study of aquifer systems is applicable to the analysis of underground resources of Africa and the Middle East arid regions.
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Yaroshevich, M. I. "Speed of Tropical Cyclone Motion in Field of Gravity Anomalies." Izvestiya, Atmospheric and Oceanic Physics 54, no. 6 (November 2018): 542–44. http://dx.doi.org/10.1134/s0001433818060154.
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Koneshov, V. N., S. A. Krylov, D. S. Loginov, and V. B. Nepoklonov. "Using the Digital Models of Gravity Anomalies for Zoning of the Earth’s Gravity Field." Izvestiya, Physics of the Solid Earth 54, no. 6 (November 2018): 964–70. http://dx.doi.org/10.1134/s1069351318060071.
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Singh, Bijendra, and D. Guptasarma. "New method for fast computation of gravity and magnetic anomalies from arbitrary polyhedra." GEOPHYSICS 66, no. 2 (March 2001): 521–26. http://dx.doi.org/10.1190/1.1444942.
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We show that at any point the gravity field from a solid body bounded by plane surfaces and having uniform density can be computed as a field from a fictitious distribution of surface mass‐density on the same body. The surface mass density at every surface element is equal to the product of the volume density of the body and the scalar product of (1) the unit outward vector normal to that surface element and (2) the position vector of the surface element with respect to the point of observation. Accordingly, the contribution to the gravity field from any plane surface of the body vanishes if the observation point lies in the plane of that surface. As a result, we can compute the gravity field everywhere, including points inside, on the surface, on an edge, or at a corner of the body where more than two surfaces meet. This new result lets us compute the gravity field using exactly the same simple procedure as for the magnetic field of a uniformly magnetized object, computed from an equivalent surface distribution of magnetic pole density. To get the gravity field while computing the magnetic field, one simply uses the product of this surface mass density and the universal gravitational constant instead of the surface magnetic pole density. Therefore, the same computer program can be used to compute the gravity, the magnetic field, or both simultaneously. This simple and novel approach makes the numerical computations much faster than all other previously published schemes.
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Sun, Yanyun, Wencai Yang, Xiangzhi Zeng, and Zhiyong Zhang. "Edge enhancement of potential field data using spectral moments." GEOPHYSICS 81, no. 1 (January 1, 2016): G1—G11. http://dx.doi.org/10.1190/geo2014-0430.1.
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Edge enhancement in potential-field data helps geologic interpretation, where the lineaments on the potential-field frequently indicate subsurface faults, contacts, and other tectonic features. Therefore, a variety of edge-enhancement methods have been proposed for locating edges, most of which are based on the horizontal or vertical derivatives of the field. However, these methods have several limitations, including thick detected boundaries, blurred response to low-amplitude anomalies, and sensitivity to noise. We have developed the spectral-moment method for detecting edges in potential-field anomalies based on the second spectral moment and its statistically invariable quantities. We evaluated the spectral-moment method using synthetic gravity data, EGM-2008 gravity data, and the total magnetic field reduced to the pole. Compared with other edge-enhancing filters, such as the total horizontal derivative (TDX), profile curvature, curvature of the total horizontal gradient amplitude, enhancement of the TDX using the tilt angle, theta map, and normalized standard deviation, this spectral-moment method was more effective in balancing the edges of different-amplitude anomalies, and the detected lineaments were sharper and more continuous. In addition, the method was also less sensitive to noise than were the other filters. Compared with geologic maps, the edges extracted by the spectral-moment method from gravity and the magnetic data corresponded well with the geologic structures.
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Korte, Monika, and Mioara Mandea. "Geopotential field anomalies and regional tectonic features – two case studies: southern Africa and Germany." Solid Earth 7, no. 3 (May 9, 2016): 751–68. http://dx.doi.org/10.5194/se-7-751-2016.
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Abstract. Maps of magnetic and gravity field anomalies provide information about physical properties of the Earth's crust and upper mantle, helpful in understanding geological conditions and tectonic structures. Depending on data availability, whether from the ground, airborne, or from satellites, potential field anomaly maps contain information on different ranges of spatial wavelengths, roughly corresponding to sources at different depths. Focussing on magnetic data, we compare amplitudes and characteristics of anomalies from maps based on various available data and as measured at geomagnetic repeat stations. Two cases are investigated: southern Africa, characterized by geologically old cratons and strong magnetic anomalies, and the smaller region of Germany with much younger crust and weaker anomalies. Estimating lithospheric magnetic anomaly values from the ground stations' time series (repeat station crustal biases) reveals magnetospheric field contributions causing time-varying offsets of several nT in the results. Similar influences might be one source of discrepancy when merging anomaly maps from different epochs. Moreover, we take advantage of recently developed satellite potential field models and compare magnetic and gravity gradient anomalies of ∼ 200 km resolution. Density and magnetization represent independent rock properties and thus provide complementary information on compositional and structural changes. Comparing short- and long-wavelength anomalies and the correlation of rather large-scale magnetic and gravity anomalies, and relating them to known lithospheric structures, we generally find a better agreement in the southern African region than the German region. This probably indicates stronger concordance between near-surface (down to at most a few km) and deeper (several kilometres down to Curie depth) structures in the former area, which can be seen to agree with a thicker lithosphere and a lower heat flux reported in the literature for the southern African region.
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LaFehr, T. R. "Standardization in gravity reduction." GEOPHYSICS 56, no. 8 (August 1991): 1170–78. http://dx.doi.org/10.1190/1.1443137.
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Gravity reduction standards are needed to improve anomaly quality for interpretation and to facilitate the joining together of different data sets. To the extent possible, data reduction should be quantitative, objective, and comprehensive, leaving ambiguity only to the interpretation process that involves qualitative, subjective, and geological decisions. The term (Bouguer anomaly) describes a field intended to be free of all nongeologic effects—not modified by a partial geologic interpretation. Measured vertical gradients of gravity demonstrate considerable variation but do not suggest, as often reported, that the normal free‐air gradient is in error or needs to be locally adjusted. Such gradients are strongly influenced by terrain and, to a lesser extent, by the same geologic sources which produce Bouguer anomalies. A substantial body of existing literature facilitates the comprehensive treatment of terrain effects, which may be rigorously implemented with current computer technology. Although variations in topographic rock density are a major source of Bouguer anomalies, a constant density appropriate to the area under investigation is normally adopted as a data reduction standard, leaving a treatment of the density variations to the interpretation. A field example from British Columbia illustrates both the variations in vertical gravity gradients which can be encountered and the conclusion that the classical approach to data reduction is practically always suitable to account for the observed effects. Standard data reduction procedures do not (and should not) include reduction‐to‐datum. The interpreter must be aware, however, that otherwise “smooth” regional Bouguer anomalies caused by regional sources do contain high‐frequency components in areas of rugged topography.
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Trojanowicz, Marek, Magdalena Owczarek-Wesołowska, Lubomil Pospíšil, and Olgierd Jamroz. "Determination of the Selected Gravity Field Functionals by the GGI Method: A Case Study of the Western Carpathians Area." Applied Sciences 10, no. 21 (November 6, 2020): 7892. http://dx.doi.org/10.3390/app10217892.
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In this paper, some features of the local disturbing potential model developed by the GGI method (based on Geophysical Gravity Inversion) were analyzed. The model was developed for the area of the Western Carpathians covering the Polish–Slovak border. A detailed assessment of the model’s property was made regarding the accuracy of the disturbing potential values (height anomalies), gravity values, complete Bouguer anomalies (CBA), and differences between geoid undulations and height anomalies (N−ζ). Obtained accuracies of the GGI quasigeoid model (in terms of standard deviation of the residuals to the reference quasigeoid models) were at the level of ±2.2 cm for Poland and ±0.9 cm for the Slovak area. In terms of gravity, there was shown dependence of the accuracy of the GGI model on the digital elevation model (DEM) resolution, the point height, the density of gravity data used, and used reference density of topography model. The best obtained results of gravity prediction were characterized by an error of approximately 1 mGal. The GGI approach were compared with classical gravity prediction methods (using CBA and topographic-isostatic anomalies supported by Kriging prediction), getting very similar results. On the basis of the GGI model, CBA and differences (N−ζ) were also determined. The strong dependence of resolution of the CBA model obtained by GGI approach, on the size of the constant density zones, has been demonstrated. This significantly reduces the quality of such a model. The crucial importance of the topographic masses density model for both determined values (CBA and (N−ζ)) was also indicated. Therefore, for determining these quantities, all available information on topographic mass densities should be used in modelling.
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BUSBY, J. P., and N. J. P. SMITH. "The nature of the Variscan basement in southeast England: evidence from integrated potential field modelling." Geological Magazine 138, no. 6 (November 2001): 669–85. http://dx.doi.org/10.1017/s0016756801005751.
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The Variscides of southeast England are buried beneath post-Carboniferous cover. Interpretations of the basement are based mainly on deep boreholes. Geophysical signatures from the basement are contained within the regional gravity and magnetic data. A gravity stripping exercise has been undertaken to remove the gravitational effect of the post-Variscan cover to generate a residual gravity map. This map is interpreted along with integrated potential field modelling along four long interconnected profiles and compared with a revised pre-Permian subcrop map. The magnetic evidence suggests that Precambrian magnetic basement of the Midlands Microcraton has been buried southwards by north-vergent Variscan thusting over the foreland. North of the Variscan Front, short-wavelength anomalies superimposed upon this deep Precambrian source are due to shallower Silurian and Carboniferous volcanic rocks. Many residual gravity lows within the Rhenohercynian zone may be related to thick, low-density Devonian basins. In the English Channel a change in geophysical signature occurs north of the Portland–Wight Fault, coinciding with phyllites in the basement. Models are presented in which the English Channel magnetic anomalies originate within the pre-Permian basement. Comparisons with anomalies in the Southwestern Approaches suggest that the Portland–Wight Thrust is a terrane boundary, possibly a subduction-related suture, implying southerly directed Variscan subduction.
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Nguyen, V. S., Yu M. Neiman, T. D. Tran, T. T. Phung, T. T. H. Le, and P. S. Nguyen. "Determination of gravity anomalies in the waters of Viet Nam and around using CryoSat-2 space altimetry." Geodesy and Cartography 983, no. 5 (June 20, 2022): 19–27. http://dx.doi.org/10.22389/0016-7126-2022-983-5-19-27.
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The purpose of this study is to determine marine gravity anomalies with high accuracy using the CryoSat-2 satellite altimetry data in the Middle Vietnamese Sea and the adjacent territory. For this, the mentioned data and the process of determining gravity anomalies from the CryoSat-2 data were analyzed. The record from 818 GNSS-leveling points in Vietnam were used to evaluate and select the best global gravity field model for use in the calculation process. The findings from 31 gauge tidal were also used to assess and select the best mean dynamic topography model for the study area. Marine gravity anomalies in the study area were calculated using data from the CryoSat-2 satellite altimeter at 72 483 measurement points. The calculated results are compared with the ship-derived gravity anomalies at 1025 measurement points for assessment. The research results show that of the Earth Geopotential Model EIGEN6C4 and the Mean Dynamic Topography Model DTU15MDT are the most suitable for the research area. The accuracy of satellite-derived gravity anomalies, calculated from the CryoSat-2 satellite altimetry data in the study area, reaches ±1,18 mGal. Compared to the available results in the study area, this accuracy is the highest.
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FUMITA, NORIYUKI. "QUANTUM VACUUM AND ANOMALIES." International Journal of Modern Physics A 10, no. 17 (July 10, 1995): 2579–88. http://dx.doi.org/10.1142/s0217751x95001224.
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Chiral, conformal and ghost number anomalies are discussed from the viewpoint of the quantum vacuum in Hamiltonian formalism. After introducing the energy cutoff, we derive known anomalies in a new way. We give an interpretation of the anomalies in connection with the zero-point fluctuation of bosonic or fermionic field. We first point out that the chiral U(1) anomaly is understood as the creation of the chirality at the bottom of the regularized Dirac sea in classical electromagnetic field. In the study of the (1+1)-dimensional quantum vacuum of matter field coupled to the gravity, we give a physically intuitive picture of the conformal anomaly. The central charges are evaluated from the vacuum energy. We clarify that the non-Hermitian regularization factor of the vacuum energy is responsible for the ghost number anomaly.
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Alarifi, Saad S. "Structural implications of potential field data on Southeastern North America." Journal of Geophysics and Engineering 19, no. 2 (April 1, 2022): 142–56. http://dx.doi.org/10.1093/jge/gxac005.
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Abstract The fault system of Eastern Piedmont could be extensive in the East of the USA. Debates remain regarding the sutures zone, contacts and faults between terranes, especially underneath the coastal sediment. However, in this study, a new interpretation of the structures and contacts of the southeastern margin was based on regional land gravity anomaly and magnetic anomaly maps. To delineate and investigate the subsurface geological structures in the southern Appalachian belt and underneath the coastal sediment that covers the southeastern half of the study area, the gravity and magnetic maps were subjected to several filter techniques. The anomalies maps were enhanced by applying the reduction to pole (RTP), analytical signal (AS), tilt derivative (TDR), horizontal gradient (HG), direction filter and power spectrum techniques. The power spectrum filter was applied to separate the regional-residual anomaly. The results of regional anomaly maps display elongate high amplitude anomalies lie in the south that are related to deep-seated igneous mafic intrusive and basaltic lavas emplacement. The directional filter was used to eliminate the sutural trend of the Jurassic dikes that intruded the study area. The result displays the structural contacts clearly after removing the anomalies of the Jurassic. Finally, the edge detection filters (TDR, HG, AS) from the gravity and magnetic maps helped in mapping the anomaly contact of the subsurface bodies. The apparent structural signature of the interpreted contacts confirmed the presence of these structural features in all edge detection methods.
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Eshagh, Mehdi, Andenet A. Gedamu, and Tulu B. Bedada. "Regional Recovery of Gravity Anomaly from the Inversion of Diagonal Components of GOCE Gravitational Tensor: A Case Study in Ethiopia." Artificial Satellites 53, no. 2 (June 1, 2018): 55–74. http://dx.doi.org/10.2478/arsa-2018-0006.
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Abstract The tensor of gravitation is traceless as the gravitational field of the Earth is harmonic outside the Earth’s surface. Therefore, summation of the 2nd-order horizontal derivatives on its diagonal components should be equal to the radial one but with the opposite sign. The gravity field can be recovered locally from either of them, or even their combination. Here, we use the in-orbit diagonal components of the gravitational tensor measured by the gravity field and steady state ocean circulation explorer (GOCE) mission for recovering gravity anomaly with a resolution of 1°×1° at sea level in Ethiopia. In order to solve the system of equations, derived after discretisation of integral equations, the Tikhonov regularisation is applied and the bias of this regularisation is estimated and removed from the estimated gravity anomalies. The errors of the anomalies are estimated and their significance of recovery from these diagonal components is investigated. Statistically, the difference between the recovered anomalies from each scenario is not significant comparing to their errors. However, their joint inversion of the diagonal components improved the solution by about 1 mGal. Furthermore, the inversion processes are better stabilised when using errors of the input data compared with its exclusion, but at the penalty of degradation in accuracy of the estimates.
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AL-Khafaji, Wadhah Mahmood Shakir. "Analyzing Gravity and Magnetic Data for the Detection of Deep-Seated Faults and Faults within the Sedimentary Cover Near Habbanieyah and Razzaza Lakes in the Middle of Iraq." Iraqi Geological Journal 54, no. 2C (September 30, 2021): 29–38. http://dx.doi.org/10.46717/igj.54.2c.3ms-2021-09-22.
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This research deals with the processing and analyzing of magnetic and gravitational data for an area covering the region of Habbanieyah - Razzaza Lakes and its adjacent areas. The study includes data processing and mapping of the total gravity and magnetic anomalies for only the concerned region, then separating the residual anomalies by adopting the polynomial regression graphical method. The residual gravity anomaly reflects the variations of rock densities within the sedimentary cover. The horizontal gradient filter has been applied to the residual gravity anomaly in order to conduct the locations of fault planes within the sedimentary cover where sudden variations of gravity field take place. The quantitative interpretation for both gravity and magnetic anomalies yielded a preliminary determination for the depth to the center of major faults within the sedimentary cover. By constructing a gravity model along a profile which directed NE-SW and passing through the middle part of the study region, depth to the center of the effective faults found. This depth variation is due to the effect of tectonic activity which produced a set of faults, such faults caused the upward and downward structural motions and were responsible for positioning the deep high density causative slabs of bedrock. The residual magnetic field quantitative interpretation along two profiles crosses over anomalies at the NE and SW parts of the region yielded the depth to the top of magnetized basement rocks. The difference in depth of the basement rocks and the shifted anomaly locations reflects the effect of tectonic activity which may relate to a strike slip faulting in the higher depths.
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Varga, M., and J. Stipčević. "Gravity anomaly models with geophysical interpretation of the Republic of Croatia, including Adriatic and Dinarides regions." Geophysical Journal International 226, no. 3 (May 10, 2021): 2189–99. http://dx.doi.org/10.1093/gji/ggab180.
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SUMMARY Models of gravity corrections and anomalies are created and distributed over the territory of the Republic of Croatia, including the Adriatic and Dinarides regions. Published models cover the study area between 42.0°N < φ < 46.6°N and 13.0°E < λ < 19.5°E with a 1′ × 1′ resolution. Distributed models include gravity corrections and anomalies of normal gravity, atmosphere, free air, Bouguer, terrain, complete Bouguer and topographic–isostatic according to the Airy–Heiskanen model. A high-resolution digital elevation/bathymetry model was prepared from SRTMv3.0 and GEBCO2019 models. It was then used for the computation of topographic and topographic–isostatic gravity effects using rectangular prisms with constant crustal density. Gridding of the scattered gravity data was performed with the Kriging interpolation method using complete Bouguer anomalies by implementing the remove–grid–restore methodology. Developed models were interpreted providing insights into the topography-reduced (anomalous) Earth’s gravity field reflecting the variations in mass/density distribution within the crust and upper mantle over the study area.
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Klokočník, Jaroslav, Jan Kostelecký, Lenka Varadzinová, Aleš Bezděk, and Gunther Kletetschka. "A Gravity Search for Oil and Gas and Groundwater in Egypt Using the Strike Angles Derived from EIGEN 6C4." Applied Sciences 10, no. 24 (December 15, 2020): 8950. http://dx.doi.org/10.3390/app10248950.
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We correlate the gravity aspects (descriptors), namely the strike angles, derived from a recent gravity field model, with the known oil, gas and groundwater deposits/reservoirs and hypothetical paleolakes with the locations of archaeological sites. This allows us to extrapolate the investigation, by analogy, to unknown regions. The gravity aspects, derived from the EIGEN 6C4 gravity field model, are used, together with EMAG 2 magnetic anomalies and ETOPO 1 topography model, for the investigation of oil, gas and water deposits in Egypt. One of the gravity aspects, s/c strike angle, is significantly combed (oriented in one direction locally) in places where the known deposits exist. However, they are combed also in some other places. This may be used as a guide as to where to seek new and promising deposits. Accounting for the combed strike angles and the relationship between gravity anomalies and height differences, we reconstructed potential paleolakes under thick sand layers in the Great Sand Sea, Western Egypt (our previous work), and between Kharga and Toshka, Southern Egypt (this work), consistent with the known archaeological sites.
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Silva, João B. C., and Valéria C. F. Barbosa. "Interactive gravity inversion." GEOPHYSICS 71, no. 1 (January 2006): J1—J9. http://dx.doi.org/10.1190/1.2168010.
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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.
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Barrows, Larry, and John D. Fett. "A high‐precision gravity survey in the Delaware Basin of southeastern New Mexico." GEOPHYSICS 50, no. 5 (May 1985): 825–33. http://dx.doi.org/10.1190/1.1441957.
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Since 1974, the Department of Energy has been studying bedded salt deposits in southeastern New Mexico as a possible location for disposing of defense‐generated transuranic and low‐level radioactive wastes. The program, known as the Waste Isolation Pilot Plant, includes intensive geologic characterization of about [Formula: see text] and construction of an underground test facility. The gravity survey reported here is part of the geologic site characterization. The gravity survey was conducted to delineate structural features near and at the proposed site. However, during the survey the gravity field was found to be dominated by effects of lateral density variations within relatively flat‐lying strata. Particularly distinctive is a pattern of elongate negative anomalies about one‐half mGal in amplitude. Boreholes in the anomalies encountered normal stratigraphy and no unusual geologic structures. However, borehole densilogs showed lower densities and uphole velocity surveys showed lower acoustic velocities than are measured outside of the anomalies. The low densities adequately account for the observed gravity anomalies. The regional stratigraphy contains water‐soluble minerals (halite, polyhalite, anhydrite‐gypsum, carbonates). Much of this material has dissolved and the region has been identified as a karstland. At the site, dissolution is slowly affecting the Rustler formation overlying the main salt‐bearing units. The low rock densities, associated with the negative gravity anomalies, are interpreted as due to alteration in the vicinity of solution conduits within the Rustler formation. This interpretation is supported by (1) partial coincidence between the negative gravity anomalies and closed topographic depressions (alluvial dolines); (2) greater anhydrite‐to‐gypsum conversion detected in boreholes within the anomalies; and (3) solution conduits encountered in one of the boreholes.
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Kwok, Yue‐Kuen. "Conjugate complex variables method for the computation of gravity anomalies." GEOPHYSICS 54, no. 12 (December 1989): 1629–37. http://dx.doi.org/10.1190/1.1442631.
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Using conjugate complex variables, a generalized method is presented to derive formulas to calculate first‐ and higher‐order derivatives of the gravity potential due to selected mass models. Double integrals in the computation of gravity‐gradient anomalies are transformed into complex contour integrals. Analytical expressions for higher‐order derivatives of the gravitational potential in arbitrary directions due to two‐dimensional (2‐D) polygonal mass models are derived. The method is extended to 2‐D polygonal bodies whose density contrasts vary with depth and horizontal distance and can be generalized to deal with 2‐D bodies of any shape. The vertical gravity field and its first derivatives due to a homogeneous radially symmetric body are also computed using conjugate complex variables. Derivation of gravity and gravity gradient formulas generally is greatly simplified by the use of complex variables.
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Abdelrahman, E. M., A. I. Bayoumi, and H. M. El‐Araby. "A least‐squares minimization approach to invert gravity data." GEOPHYSICS 56, no. 1 (January 1991): 115–18. http://dx.doi.org/10.1190/1.1442946.
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The interpretation of gravity data often involves initial steps to eliminate or attenuate unwanted field components in order to isolate the desired anomaly (e.g., residual‐regional separations). These initial filtering operations include, for example, the radial weights methods (Griffin, 1949; Elkins, 1951; Abdelrahman et al., 1990), the fast Fourier transform methods (Bhattacharyya, 1965; Clarke, 1969; Meskó, 1969, 1984, Botezatu, 1970), the rational approximation techniques (Agarwal and Lal, 1971) and recursion filters (Bhattacharyya, 1976), and the bicubic spline approximation techniques (Bhattacharyya, 1969; Inoue, 1986). The derived local gravity anomalies are then geologically interpreted to derive depth estimates, often without properly accounting for the uncertainties introduced by the filtering process. When filters are applied to observed data, the filters often cause serious distortions in the shape of the gravity anomalies (Hammer, 1977). Thus the filtered gravity anomalies generally yield unreliable geologic interpretations (Rao and Radhakrishnamurthy, 1965; Hammer, 1977; Abdelrahman et al., 1985, 1989.
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Liu, Xin, Guihua Hui, Jinyun Guo, Tinghui Zhang, and Menghao Song. "Inversion of Deflection of the Vertical in the South China Sea Using ICESat-2 Sea Surface Height Data." Remote Sensing 15, no. 1 (December 21, 2022): 30. http://dx.doi.org/10.3390/rs15010030.
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The traditional altimetry satellites based on pulse-limited radar altimeter only calculate along-track deflection of the vertical (DOV), which results in poorer precision of the prime vertical component than that of the meridian component and limits the precision of the marine gravity field inversion. We expect an improvement in the higher precision prime vertical component using the Ice, Cloud and land Elevation Satellite 2 (ICESat-2) sea surface height (SSH) data. In this paper, the 2′ × 2′ gridded DOVs derived from along-beam DOVs, cross-beam DOVs, and joint along-cross beam DOVs in the South China Sea (SCS; 0°–23°N, 103°–120°E) are calculated with the weighted least squares method, respectively. The inverse Vening–Meinesz (IVM) formula is applied to derive 2′ × 2′ gravity anomalies over the SCS from ICESat-2-derived gridded DOVs. In addition, the XGM2019e_2159-DOV and SIO V31.1-DOV models are used to assess the precision of the gridded DOVs. The XGM2019e_2159-GRA, SIO V31.1-GRA models, and ship-borne gravity anomalies are also adopted to evaluate the quality of gravity anomalies. The results show that the gridded DOVs calculated by the joint along-cross beam DOVs have the highest precision among the three gridded DOVs determined by ICESat-2. The precision of difference between gravity anomalies derived from the joint along-cross beam DOV and the above verification data are higher than those derived from the along-beam and cross-beam DOVs. We conclude that the joint along-cross beam DOV can effectively improve the precision of the gridded DOV, which is conducive to the inversion of a high-precision marine gravity field.
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Ueda, Yoshio, Ryuji Kubota, and Jiro Segawa. "Magneto‐gravity response function and its application to the Daito Ridge." GEOPHYSICS 67, no. 1 (January 2002): 110–16. http://dx.doi.org/10.1190/1.1451383.
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A magneto‐gravity response function, which shows a phase relationship between magnetic and gravity anomalies caused by a common source body with a constant density‐to‐magnetization ratio, is derived for determining the magnetization direction of a source body for 2‐D and 3‐D cases. The validity of the method is demonstrated through application to test data and to field anomalies from the Daito Ridge. The Daito Ridge is found to be magnetized in the present main field direction, contrary to shallow inclinations suggested by studies of Deep Sea Drilling Project (DSDP) sediment cores. The strong normal magnetization is ascribed to high magnetic susceptibility and/or viscous remanent magnetization.
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Cook, Frederick A., John L. Varsek, and Jeffrey B. Thurston. "Tectonic significance of gravity and magnetic variations along the Lithoprobe Southern Canadian Cordillera Transect." Canadian Journal of Earth Sciences 32, no. 10 (October 1, 1995): 1584–610. http://dx.doi.org/10.1139/e95-128.
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Correlation of potential field data to regional geological features within the Lithoprobe southern Canadian Cordillera transect corridor allows characterization of anomaly patterns according to their likely sources. Long-wavelength Bouguer gravity anomalies are attributed to isostatic effects of topography, which in most areas is compensated. Two notable exceptions occur: in the Foreland belt a large positive isostatic anomaly is likely due to mechanical support of topography formed as Cordilleran thrust sheets were emplaced over the thick craton, and on the west coast, isostatic anomalies are related to active subduction. Long-wavelength magnetic anomalies in the Foreland belt are associated with cratonal basement beneath the thrust sheets, and these can be followed westward to near the Omineca belt. A prominent positive magnetic anomaly along the western Coast belt is probably associated with mafic rocks generated during subduction. Elsewhere, relatively short wavelength gravity and magnetic anomalies correlate well with either plutons (both gravity and magnetic), volcanics (primarily magnetics), or faults (magnetics) within the region of accreted terranes.
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von Frese, Ralph R. B., Michael B. Jones, Jeong Woo Kim, and Wen Sheng Li. "Spectral correlation of magnetic and gravity anomalies of Ohio." GEOPHYSICS 62, no. 1 (January 1997): 365–80. http://dx.doi.org/10.1190/1.1444139.
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Geologic interpretation of Ohio's magnetic or gravity anomalies is hindered by the effects of anomaly superposition and source ambiguity inherent to potential field analysis. A common approach to minimizing interpretational ambiguities is to consider analyses of anomaly correlations. A spectral procedure is adapted which correlates anomaly fields in the frequency domain to produce filters separating positively and negatively correlated, as well as null correlated features. The correlation filter passes or rejects wavenumbers between coregistered fields based on the correlation coefficient between common wavenumbers as given by the cosine of their phase difference. This procedure is applied to reduced‐to‐pole magnetic and first vertical derivative gravity anomalies of Ohio for mapping correlative magnetization and density contrasts within the basement rocks. The analysis reveals predominantly positive correlations between anomaly maxima and minima. Correlative anomaly maxima may be generally modeled as mafic bodies of the upper crust. They map out a possible dike complex in northwestern Ohio, a batholith as a possible source of volcanic rocks in southwestern Ohio, and numerous mafic bodies related presumably to Keweenawan rifting and Grenville tectonics. Correlative anomaly minima include several isolated features that may define felsic terranes of the upper crust, and ringed features around some of the larger mafic bodies which also may contain significant edge‐effect components. A large circular feature in south‐central Ohio involves correlative minima of a possible anorthosite body that is ringed by an inversely correlative zone of positive density and negative magnetization contrasts. Another prominent negative correlation involves an extensive area of possible extrusive rocks with positive magnetization and negative density contrasts just north of the batholith in southwestern Ohio.
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Tenzer, Robert, and Peter Vajda. "Global atmospheric effects on the gravity field quantities." Contributions to Geophysics and Geodesy 39, no. 3 (January 1, 2009): 221–36. http://dx.doi.org/10.2478/v10126-009-0008-2.
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Global atmospheric effects on the gravity field quantitiesWe compile the global maps of atmospheric effects on the gravity field quantities using the spherical harmonic representation of the gravitational field. A simple atmospheric density distribution is assumed within a lower atmosphere (< 6 km). Disregarding temporal and lateral atmospheric density variations, the radial atmospheric density model is defined as a function of the nominal atmospheric density at the sea level and the height. For elevations above 6 km, the atmospheric density distribution from the United States Standard Atmosphere 1976 is adopted. The 5 × 5 arc-min global elevation data from the ETOPO5 are used to generate the global elevation model coefficients. These coefficients (which represent the geometry of the lower bound of atmospheric masses) are utilized to compute the atmospheric effects with a spectral resolution complete to degree and order 180. The atmospheric effects on gravity disturbances, gravity anomalies and geoid undulations are evaluated globally on a 1 × 1 arc-deg grid.
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Zhang, Jianzhong, Benshan Zhong, Xixiang Zhou, and Yun Dai. "Gravity anomalies of 2-D bodies with variable density contrast." GEOPHYSICS 66, no. 3 (May 2001): 809–13. http://dx.doi.org/10.1190/1.1444970.
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A new method is presented to compute gravity anomalies that result from 2-D bodies with variable density contrast. The cross‐section of a body is approximated by a polygon. Density is assumed to vary as any order of polynomial function with depth and lateral position. Results calculated by the proposed method for models with variable density contrast compare well with other methods. Liaohe basin, northeast China, is modeled from field gravity anomalies using the formulas given, showing the method is valid and effective.
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Vasanthi, A., and K. Mallick. "Bouguer gravity anomalies and occurrence patterns of kimberlite pipes in Narayanpet-Maddur Regions, Andhra Pradesh, India." GEOPHYSICS 70, no. 1 (January 2005): J13—J24. http://dx.doi.org/10.1190/1.1852778.
Full textAbstract:
The Narayanpet Kimberlite field, that lies southwest of Hyderabad, the capital city of Andhra Pradesh, India, hosts a number of kimberlite pipes. These pipes appear to be randomly positioned. However, based on regional geologic structures revealed by Bouguer gravity anomalies, especially in a regional gravity map, their locations form a definite pattern. In the Narayanpet-Maddur region, regional Bouguer gravity contours exhibit some features of geologic interest: (1) the eastward convex regional contours show an increase in convexity from the Maddur and Kotakonda area on the east to Narayanpet on the west, (2) convexity is maximum in the vicinity of Narayanpet, where a large number of Kimberlite pipes occur nearly parallel to the regional contour, and (3) between Narayanpet and the Maddur-Kotakonda region, kimberlite pipes occur at intersections of three eastward, convex concentric zones with four lineaments, one trending northeast-southwest and the other three nearly east-west. These linear trends are believed to be radial, extensional, deep-fracture zones, through which kimberlite magma erupted about 1100 Ma. Modeling the residual gravity anomaly over one of the four profiles shows fairly good agreement between observed and computed fields. Based on analysis of Bouguer gravity anomalies and modeling of the residual gravity field, likely locations for kimberlite pipes are the contact zones between granite plutons and the country rocks that coincide with the northeast-southwest–trending radial faults that pass through Narayanpet and Kotakonda to the south and through Kazipur to the north.
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Izquierdo, Kristel, Vedran Lekić, and Laurent G. J. Montési. "A Bayesian approach to infer interior mass anomalies from the gravity data of celestial bodies." Geophysical Journal International 220, no. 3 (December 3, 2019): 1687–99. http://dx.doi.org/10.1093/gji/ggz544.
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SUMMARY Inversions of planetary gravity are aimed at constraining the mass distribution within a planet or moon. In many cases, constraints on the interior structure of the planet, such as the depth of density anomalies, must be assumed a priori, to reduce the non-uniqueness inherent in gravity inversions. Here, we propose an alternative approach that embraces the non-uniqueness of gravity inversions and provides a more complete view of related uncertainties. We developed a Transdimensional Hierarchical Bayesian (THB) inversion algorithm that provides an ensemble of mass distribution models compatible with the gravitational field of the body. Using this ensemble of models instead of only one, it is possible to quantify the range of interior parameters that produce a good fit to the gravity acceleration data. To represent the interior structure of the planet or moon, we parametrize mass excess or deficits with point masses. We test this method with synthetic data and, in each test, the algorithm is able to find models that fit the gravity data of the body very well. Three of the target or test models used contain only point mass anomalies. When all the point mass anomalies in the target model produce gravity anomalies of similar magnitudes and the signals from each anomaly are well separated, the algorithm recovers the correct location, number and magnitude of the point mass anomalies. When the gravity acceleration data of a model is produced mostly by a subset of the point mass anomalies in the target model, the algorithm only recovers the dominant anomalies. The fourth target model is composed of spherical caps representing lunar mass concentration (mascons) under major impact basins. The algorithm finds the correct location of the centre of the mascons but fails to find their correct outline or shape. Although the inversion results appear less sharp than the ones obtained by classical inversion methods, our THB algorithm provides an objective way to analyse the interior of planetary bodies that includes epistemic uncertainty.