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Accuracy assessment of high and ultra high-resolution combined GGMs, and recent satellite-only GGMs - Case studies of Poland and Ethiopia

Godah Walyeldeen, Szelachowska Małgorzata, Gedamu Andenet A.

Reports on Geodesy and Geoinformatics

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2024

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Vol. 117

38--44

EN

The launch of dedicated satellite gravity missions (CHAMP, GRACE, GOCE, and GRACE-FO), as well as the availability of gravity data from satellite altimetry and terrestrial/airborne gravity measurements have led to a growing number of Global Geopotential Models (GGMs) developed. Thus, the evaluation of GGMs is necessary to ensure their accuracy in recovering the Earth's gravity field on local, regional, and global scales. The main objective of this research is to assess the accuracy of recent GGMs over Poland in Central Europe and Ethiopia in East Africa. Combined GGMs of high (degree and order (d/o) 2190) and ultra high-resolution (d/o 5540) as well as five satellite-only GGMs were evaluated using gravity data from absolute gravity measurements and airborne gravity surveys over Poland and Ethiopia, respectively. Based on this evaluation, the estimated accuracy of the high-resolution combined GGM is at the level of 2 mGal. The estimated accuracy for the ultra-high-resolution combined GGM is ~2.5 times lower. The satellite-only GGMs investigated recover the gravity signal at an accuracy level of 10 mGal and 26 mGal, for the areas of Poland and Ethiopia, respectively. When compensating for the omitted gravity signal using a high-resolution combined GGM and the topography model, an accuracy of 2 mGal can be achieved.

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Application of direct source parameter imaging (direct local wave number) technique to the 2D gravity anomalies for depth determination of some geological structures

Alvandi Ahmad, Toktay Hazel Deniz, Nasri Sara

Acta Geophysica

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2022

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Vol. 70, no 2

659--667

EN

Analytic signal (AS) is a complex quantity defined by two components, amplitude and phase. The intensity of changes in the phase component of the analytic signal is equal to the local wavenumber, which is used to interpret gravity data from the contact, thin dyke, and horizontal cylinder models. However, one of the disadvantages of this method is its sensitivity to noise. This paper introduces an improved local wavenumber (DSPI) based on a direct analytic signal (DAS) that is more accurate in determining the depth of potential features on gravity anomalies. This method was first tried to determine the depth values of noisy and noiseless 2D synthetic model structures. After theoretical approval, the method was examined on two gravity field data from Iran (the Gol-e-Gohar iron ore mine, Kerman) and Canada (Mobrun orebody, near Noranda). The results obtained from the DSPI method have an excellent agreement with the drilling information, Radial amplitude spectrum, and the Euler deconvolution method.

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Geophysical depth to basement research in the SW sector of the Santa Lucía Basin, southern Uruguay

Corbo-Camargo Fernando, Ramos Julián, Rodríguez Pablo, De los Santos Jorge

Acta Geophysica

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2021

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Vol. 69, no. 4

1287--1296

EN

The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2 . In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profle that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C.

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Applying the Tilt depth and Tilt Euler techniques of gravity data to decipher the basement depth in Sichuan Basin, China

Chen Qing, Dong Yunpeng, Tan Xianfeng, Wang Jiabei, Huang Xiaoyu, Chen Hao

Acta Geophysica

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2021

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Vol. 69, no. 6

2173--2186

EN

The tilt angle (i.e., TDR) provides an efficient way to recognize the horizontal locations of multi-source geological bodies at different depths and inclination angles. The tilt-depth method was initially derived by applying magnetic formulas and used to calculate the depth of magnetic sources. Recently researchers have attempted to extend this method to interpret depths in gravity field data. The tilt-depth method of gravity anomalies (i.e., GTilt-depth) could capture the depth of a buried source effectively, which makes it superior at deciphering the basement relief. Meanwhile, Tilt-Euler deconvolution (i.e., Euler deconvolution of TDR) has been utilized for estimating a source’s position from gridded data automatically, which requires no structural index. However, analytical singularities can be produced when performing inversion with the Tilt-Euler deconvolution owning to the derivatives of TDR being incalculable when the horizontal derivative is zero. The improved Tilt-Euler deconvolution provided an efficient way to eliminate analytical singularities and obtain more stable solutions. The results from the theoretical model show that the GTilt-depth method and improved Tilt-Euler deconvolution could be applied to calculate the buried depths more accurately and effectively. Application of these methods shows that they are able to capture more detailed features, and provide more straightforward and accurate results of depth, than traditional methods. Furthermore, the results obtained from the gravity data in Sichuan Basin show that the basement depth ranges from 3 to 11 km, and 3 to 7 km in the central uplift, which contains a local depression with a depth of 8 km. The basement exhibits a general pattern of “shallow in middle and deep in east and west”, which is consistent with the results revealed by gravityseismic jointly interpreted profile. This research provides a better indication of the basement structure when interpreting the regional geology in Sichuan Basin.

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Interpretation of gravity anomaly over 2D vertical and horizontal thin sheet with fnite length and width

Biswas Arkoprovo

Acta Geophysica

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2020

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Vol. 68, no. 4

1083--1096

EN

Gravity data are often used for delineation of the lateral and vertical extension of mineralized bodies buried at diferent depths. Various parameters associated with the buried bodies are the primary concern for mineral exploration purposes. Hence, a reliable and efcacious interpretation method is developed for the delineation of gravity anomaly data over the 2D vertical and horizontal sheet with fnite length and width associated with mineralized bodies. The parameters viz. amplitude coefcient (k), location (x0), depth to the top of the body (h), length of the sheet (L), and shape factor (q) for 2D vertical sheet type structure and depth (h) and width (w) of the sheet for 2D horizontal sheet were resolved. Restricting x0 and q has given very reliable results for the 2D vertical sheet, and the w for 2D horizontal sheet shows the problem of equivalence. However, in all cases, the delineated parameters are within the expected uncertainty. The present interpretation method was applied to synthetic and noisy data and three feld examples from the USA, Canada, and Sweden for mineral exploration purposes. It has also been seen that the present study is more reliable in delineating the actual structure associated with mineralized bodies for the 2D vertical and horizontal sheet-type structure. The delineated parameters are in outstanding agreement with the earlier works, borehole information and also updated the actual subsurface structure.

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Current state of art of satellite altimetry

Łyszkowicz A. B., Bernatowicz A.

Geodesy and Cartography

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2017

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Vol. 66, no. 2

259--270

EN

One of the fundamental problems of modern geodesy is precise defi nition of the gravitational fi eld and its changes in time. This is essential in positioning and navigation, geophysics, geodynamics, oceanography and other sciences related to the climate and Earth’s environment. One of the major sources of gravity data is satellite altimetry that provides gravity data with almost 75% surface of the Earth. Satellite altimetry also provides data to study local, regional and global geophysical processes, the geoid model in the areas of oceans and seas. This technique can be successfully used to study the ocean mean dynamic topography. The results of the investigations and possible products of altimetry will provide a good material for the GGOS (Global Geodetic Observing System) and institutions of IAS (International Altimetry Service). This paper presents the achievements in satellite altimetry in all the above disciplines obtained in the last years. First very shorly basic concept of satellite altimetry is given. In order to obtain the highest accuracy on range measurements over the ocean improved of altimetry waveforms performed on the ground is described. Next, signifi cant improvements of sea and ocean gravity anomalies models developed presently is shown. Study of sea level and its extremes examined, around European and Australian coasts using tide gauges data and satellite altimetry measurements were described. Then investigations of the phenomenon of the ocean tides, calibration of altimeters, studies of rivers and ice-sheets in the last years are given.

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Determination of Sedimentary Basin Basement Depth : A Space Domain Based Gravity Inversion using Exponential Density Function

Chakravarthi V., Ramamma B.

Acta Geophysica

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2015

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Vol. 63, no. 4

1066--1079

EN

An automatic inversion using ridge regression algorithm is developed in the space domain to analyze the gravity anomalies of sedimentary basins, among which the density contrast decreases with depth following a prescribed exponential function. A stack of vertical prisms having equal widths, whose depths become the unknown parameters to be estimated, describes the geometry of a sedimentary basin above the basement complex. Because no closed form analytical equation can be derivable in the space domain using the exponential density-depth function, a combination of analytical and numerical approaches is used to realize forward gravity modeling. The depth estimates of sedimentbasement interface are initiated and subsequently improved iteratively by minimizing the objective function between the observed and modeled gravity anomalies within the specified convergence criteria. Two gravity anomaly profiles, one synthetic and a real, are interpreted using the proposed technique to demonstrate its applicability.

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A priori noise and regularization in least squares collocation of gravity anomalies

Jarmołowski W.

Geodesy and Cartography

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2013

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Vol. 62, no. 2

199--216

EN

The paper describes the estimation of covariance parameters in least squares collocation (LSC) by the cross-validation (CV) technique called leave-one-out (LOO). Two parameters of Gauss-Markov third order model (GM3) are estimated together with a priori noise standard deviation, which contributes significantly to the covariance matrix composed of the signal and noise. Numerical tests are performed using large set of Bouguer gravity anomalies located in the central part of the U.S. Around 103 000 gravity stations are available in the selected area. This dataset, together with regular grids generated from EGM2008 geopotential model, give an opportunity to work with various spatial resolutions of the data and heterogeneous variances of the signal and noise. This plays a crucial role in the numerical investigations, because the spatial resolution of the gravity data determines the number of gravity details that we may observe and model. This establishes a relation between the spatial resolution of the data and the resolution of the gravity field model. This relation is inspected in the article and compared to the regularization problem occurring frequently in data modeling.

PL

Artykuł opisuje estymację parametrów kowariancji w kolokacji najmniejszych kwadratów (LSC) przy pomocy techniki kroswalidacji nazywanej leave-one-out (LOO). Wyznaczane są dwa parametry modelu Gaussa-Markova trzeciego rzędu (GM3) wraz z odchyleniem standardowym szumu a priori, które ma znaczny wpływ na macierz kowariancji złożoną z sygnału i szumu. Testy numeryczne przeprowadzono na dużym zbiorze anomalii grawimetrycznych Bouguera z obszaru centralnej części USA. Obszar ten mieści około 103000 pomiarów grawimetrycznych. Dane te wraz z regularnymi siatkami wygenerowanymi z modelu geopotencjalnego EGM2008 pozwalają na pracę z różną rozdzielczością przestrzenną i różnymi wariancjami sygnału i szumu. Odgrywa to kluczową rolę w badaniach numerycznych, ponieważ rozdzielczość przestrzenna danych grawimetrycznych wyznacza liczbę szczegółów pola siły ciężkości, które możemy obserwować i modelować. Oznacza to relację pomiędzy rozdzielczością przestrzenną danych i rozdzielczością modelu pola siły ciężkości. Związek ten jest w artykule analizowany i porównywany z problemem regularyzacji, występującym często w modelowaniu danych przestrzennych.

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50-lecie odkrycia złoża węgla brunatnego w Złoczewie

Podemski M.

Przegląd Geologiczny

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2012

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Vol. 60, nr 12

643–-645

EN

At the beginning of1962, a brown coal deposit has been discovered by the Złoczew IG-1 borehole drilled in the centre of a local negative gravity anomaly in Central Poland by the Polish Geological Institute. Thorough exploration of the deposit has established its brown coal reserves for about half a billion tons. Additionally, the discovery provedfor the first time that negative gravity anomalies could also be caused by brown coal concentrations, and not only by salt diapirs.