On: F. Bryan Davies’ discussion of “Airborne gravity is here,” by S. Hammer, and related discussions with replies by S. Hammer (GEOPHYSICS, 51, 1502–1503, July 1986).

Geophysics ◽  
1987 ◽  
Vol 52 (3) ◽  
pp. 376-376
Author(s):  
Nelson C. Steenland
Keyword(s):  
Potential Field ◽  
Complete Loss ◽  
Airborne Gravity ◽  
Space Domain

Attenuation of potential field anomalies with increasing distance from the source is, of course, independent of sampling, so the Nyquist problem may always be avoided with increased cost, as Davies pointed out. However, attenuation does produce a complete loss of some signal with increasing distance because instruments operate in a discrete or space domain. So all instruments are filters in this sense, and no amount of sampling overcomes this unfortunate characteristic.

Potential field data interpolation by Taylor series expansion

Geophysics ◽  
2021 ◽  
pp. 1-46
Author(s):  
Tao Chen ◽  
Dikun Yang
Keyword(s):  
Series Expansion ◽  
Taylor Series ◽  
Potential Field ◽  
Field Data ◽  
Taylor Series Expansion ◽  
Critical Parameters ◽  
Airborne Gravity ◽  
Query Point ◽  
Data Interpolation ◽  
Potential Field Data

Data interpolation is critical in the analysis of geophysical data when some data is missing or inaccessible. We propose to interpolate irregular or missing potential field data using the relation between adjacent data points inspired by the Taylor series expansion (TSE). The TSE method first finds the derivatives of a given point near the query point using data from neighboring points, and then uses the Taylor series to obtain the value at the query point. The TSE method works by extracting local features represented as derivatives from the original data for interpolation in the area of data vacancy. Compared with other interpolation methods, the TSE provides a complete description of potential field data. Specifically, the remainder in TSE can measure local fitting errors and help obtain accurate results. Implementation of the TSE method involves two critical parameters – the order of the Taylor series and the number of neighbors used in the calculation of derivatives. We have found that the first parameter must be carefully chosen to balance between the accuracy and numerical stability when data contains noise. The second parameter can help us build an over-determined system for improved robustness against noise. Methods of selecting neighbors around the given point using an azimuthally uniform distribution or the nearest-distance principle are also presented. The proposed approach is first illustrated by a synthetic gravity dataset from a single survey line, then is generalized to the case over a survey grid. In both numerical experiments, the TSE method has demonstrated an improved interpolation accuracy in comparison with the minimum curvature method. Finally we apply the TSE method to a ground gravity dataset from the Abitibi Greenstone Belt, Canada, and an airborne gravity dataset from the Vinton Dome, Louisiana, USA.

Imaging geologic surfaces by inverting gravity gradient data with depth horizons

Geophysics ◽  
2012 ◽  
Vol 77 (1) ◽  
pp. G1-G11 ◽  
Author(s):  
Gary Barnes ◽  
Joseph Barraud
Keyword(s):  
Potential Field ◽  
Large Scale ◽  
Airborne Gravity ◽  
Gravity Gradient ◽  
Depth Information ◽  
Total Variation Regularization ◽  
Inversion Algorithm ◽  
Pass Filter ◽  
Near Surface ◽  
Potential Field Data

The nonuniqueness problem that occurs when inverting potential field data is well known. It can, however, be surmounted by jointly inverting these data with independent data sets, incorporating depth information and regularizing the solution. The goal is to produce a geologic model that is compatible with all measured quantities, does not exceed any prescribed limits, and is geologically plausible. To achieve this, we have developed a spatially based surface inversion algorithm that solves for the geometric interface between geologic bodies. The bodies are constructed from grids of rectangular prisms that have their bottom depths adjusted by the algorithm to form the inverted surface. To solve large-scale inversions, approximations are used in the potential field calculations that allow internal matrices to be stored in sparse format with minimal loss of accuracy. The impetus for the work came from the need to combine airborne gravity gradient data with depth horizons estimated from interpreted 2D seismic profiles to form a high-resolution 3D inversion for imaging salt bodies. By treating the depth information as measurements rather than constraints, we accommodate uncertainties in these estimates. Total variation regularization is incorporated to support the sharp edges of the salt structures and to stabilize the solution. Inversions for near-surface structures also incorporate a high-pass filter to suppress the interference in the gravity gradient signal from deeper geology. The resulting optimization finds a surface that fits (in a least-squares sense) the depth information and the high-frequency content of the gravity gradient data.

Interpretation of buried basement in the southwestern Athabasca Basin, Canada, from integrated geophysical and geological datasets

2020 ◽  
Vol 21 (1) ◽  
pp. geochem2019-061
Author(s):  
Victoria Tschirhart ◽  
Sally Pehrsson ◽  
Colin Card ◽  
Eric G. Potter ◽  
Jeremy Powell ◽  
...  
Keyword(s):  
Potential Field ◽  
Physical Property ◽  
Drill Hole ◽  
Airborne Gravity ◽  
Content Type ◽  
Athabasca Basin ◽  
Basement Rocks ◽  
Gravity And Magnetic ◽  
Geophysical Surveys ◽  
Lineament Analysis

Recent discoveries of basement-hosted uranium deposits in the Patterson Lake corridor in the southwestern Athabasca Basin of Canada have brought vigorous exploration interest to the region. New lithostratigraphic constraints, geochronology and airborne geophysical surveys have dramatically improved the understanding of the host basement geology, warranting a re-examination of the remote predictive mapping and geophysical responses of the buried basement rocks. This study took a two-step approach to examine the regional basement geology and architecture. First, a mosaic of the long-wavelength response of potential field (gravity and magnetic) datasets was examined to divide the basement into regional domains based on bulk physical property variations. The interpretive geological model was then refined using textural and lineament analysis of new airborne gravity and magnetic datasets, geological drill hole logs and magnetic susceptibility measurements. The new basement map identifies and updates major features including a crustal-scale structure that separates the southern Tantato Domain from the newly defined eastern Taltson Domain. This structure may have played a role in localizing fluid flow in the Patterson Lake corridor, defining the spatial extents of structurally controlled buried felsic intrusions, and redefines the boundaries of the Taltson, Clearwater and Tantato Domains. In addition, the potential field enhancements delineated significant regional faults that controlled the geometry of Paleoproterozoic cover sequences and have implications for understanding the crustal architecture of the southern Rae Province. These new interpretations shed light on the tectonic history of the region to support on-going exploration activities and delineate regionally prospective areas in this understudied area of the Canadian Shield.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

scholarly journals Revisiting Austfonna, Svalbard with potential field methods – A new characterization of the bed topography and its physical properties

2019 ◽  
Author(s):  
Marie-Andrée Dumais ◽  
Marco Brönner
Keyword(s):  
Physical Properties ◽  
Potential Field ◽  
Gravity Data ◽  
Magnetic Data ◽  
Gravity Modeling ◽  
Airborne Gravity ◽  
Ice Thickness ◽  
Field Methods ◽  
Bed Topography ◽  
Ice Cap

Abstract. With hundreds of meters of ice, the bedrock underlying Austfonna, the largest ice cap on Svalbard, is hardly characterized in terms of topography and physical properties. Ground penetrating radar (GPR) measurements supply ice thickness estimation but the data quality is temperature-dependent, comprising uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, sub-glacial bed topography is effectively derived from gravity modeling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight of the basement distribution. This contributes to refine the range of density expected under the ice and improve the sub-ice model. From this study, a prominent magmatic N-S oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the sub-surface lithology characterized with different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted, adjusted for the potential field interpretation. When the results are compared to bed elevation maps previously produced by radio echo-sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves the understanding of the geology, assigns physical properties to the basements, and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna which influence the basal sliding rates and surges.

scholarly journals Revisiting Austfonna, Svalbard, with potential field methods – a new characterization of the bed topography and its physical properties

2020 ◽  
Vol 14 (1) ◽  
pp. 183-197
Author(s):  
Marie-Andrée Dumais ◽  
Marco Brönner
Keyword(s):  
Physical Properties ◽  
Potential Field ◽  
Gravity Data ◽  
Magnetic Data ◽  
Airborne Gravity ◽  
Ice Thickness ◽  
Field Methods ◽  
Bed Topography ◽  
Basal Sliding ◽  
Radio Echo Sounding

Abstract. With hundreds of metres of ice, the bedrock underlying Austfonna, the largest icecap on Svalbard, is hard to characterize in terms of topography and physical properties. Ground-penetrating radar (GPR) measurements supply ice thickness estimation, but the data quality is temperature dependent, leading to uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, subglacial bed topography is effectively derived from gravity modelling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight into the basement distribution. This contributes to refining the range of density expected under the ice and improving the subice model. For this study, a prominent magmatic north–south-oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the subsurface lithology, characterized by different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted and adjusted for the potential field interpretation, i.e. magnetic- and gravity-data analysis and modelling. When the results are compared to bed elevation maps previously produced by radio-echo sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves understanding of the geology; assigns physical properties to the basements; and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna, which influence the basal-sliding rates and surges.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

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