Journal ArticleDOI
Leveling aerogeophysical data using a moving differential median filter
Eirik Mauring,Ola Kihle +1 more
TLDR
In this paper, a moving differential median filter is used to minimize line-level errors and distortion of high-wavenumber anomalies when processing irregular survey lines, making the method suitable for a wide variety of data sets.Abstract:
We describe a new technique that can be used to level data collected along regular and irregular line patterns with or without tie-line control. The technique incorporates a moving differential median filter to minimize line-level errors, to level survey-line data, and to microlevel data with no tie-line control. This overcomes the problem of standard leveling methods that lose their effectiveness with irregular flight patterns. To validate the method, we use it to level very-low-frequency (VLF) electromagnetic (EM) data from a helicopter survey where flight lines are parallel. Leveling is also performed on a set of vintage aeromagnetic data from the North Sea, gathered from nonparallel flight lines. Results show that the differential median filter leveling technique is superior to the standard leveling method because it results in fewer line errors and less distortion of high-wavenumber anomalies when processing irregular survey lines, making the method suitable for a wide variety of data sets.read more
Citations
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Journal ArticleDOI
An alternative early opening scenario for the Central Atlantic Ocean
TL;DR: In this paper, an alternative scenario for the continental breakup and the Mesozoic spreading history of the Central Atlantic Ocean is proposed, based on an analysis of geophysical data (including new seismic lines, an interpretation of the newly compiled magnetic data, and satellite derived gravimetry) and recently published results which demonstrate that the opening of the central Atlantic Ocean started already during the Late Sinemurian (190-Ma), based on a new identification of the African conjugate to the ECMA and on the extent of salt provinces off Morocco and Nova Scotia.
An alternative early opening scenario for the Central Atlantic Ocean
Abstract: Abstract The opening of the Central Atlantic Ocean basin that separated North America from northwest Africa is well documented and assumed to have started during the Late Jurassic. However, the early evolution and the initial breakup history of Pangaea are still debated: most of the existing models are based on one or multiple ridge jumps at the Middle Jurassic leaving the oldest crust on the American side, between the East Coast Magnetic Anomaly (ECMA) and the Blake Spur Magnetic Anomaly (BSMA). According to these hypotheses, the BSMA represents the limit of the initial basin and the footprint subsequent to the ridge jump. Consequently, the evolution of the northwest African margin is widely different from the northeast American margin. However, this setting is in contradiction with the existing observations. In this paper, we propose an alternative scenario for the continental breakup and the Mesozoic spreading history of the Central Atlantic Ocean. The new model is based on an analysis of geophysical data (including new seismic lines, an interpretation of the newly compiled magnetic data, and satellite derived gravimetry) and recently published results which demonstrate that the opening of the Central Atlantic Ocean started already during the Late Sinemurian (190 Ma), based on a new identification of the African conjugate to the ECMA and on the extent of salt provinces off Morocco and Nova Scotia. The identification of an African conjugate magnetic anomaly to BSMA, the African Blake Spur Magnetic Anomaly (ABSMA), together with the significant change in basement topography, are in good agreement with that initial reconstruction. The early opening history for the Central Atlantic Ocean is described in four distinct phases. During the first 20 Myr after the initial breakup (190–170 Ma, from Late Sinemurian to early Bajocian), oceanic accretion was extremely slow (∼ 0.8 cm/y). At the time of Blake Spur (170 Ma, early Bajocian), a drastic change occurred both in the relative plate motion direction (from NNW–SSE to NW–SE) and in the spreading rate (an increase to ∼ 1.7 cm/y). After a small increase between Chron M25 (∼ 154 Ma, Kimmeridgian) and Chron M22 (∼ 150 Ma, Tithonian), the spreading rate slowed down to about 1.3 cm/y and remained fairly constant until Chron M0 (125 Ma, Barremian–Aptian boundary). In addition, kinematic reconstructions illustrate a significant spreading asymmetry during the early history of the Central Atlantic Ocean; the accretion rates were higher on the American side and led to the formation of more oceanic crust on this plate. We infer that this asymmetry could be related to the fact that the thermal anomaly responsible for the significant magmatism of the Central Atlantic Magmatic Province (CAMP) was preferentially located below the African plate.
Journal ArticleDOI
Ice-sheet dynamics and ice streaming along the coastal parts of northern Norway
TL;DR: In this article, the authors used bathymetric data to reconstruct the pattern and dynamics of ice-sheet flow in the fjord and shelf areas of Troms county in northern Norway.
Journal ArticleDOI
Crustal and basin evolution of the southwestern Barents Sea: From Caledonian orogeny to continental breakup
TL;DR: In this article, a new generation of aeromagnetic data documents the post-Caledonide rift evolution of the southwestern Barents Sea (SWBS) from the Norwegian mainland up to the continent-ocean transition, where the Caledonian nappes and thrust sheets, well-constrained onshore, swing from a NE-SW trend onshore Norway to NW-SE/NNW-SSE across the SWBS platform area.
Journal ArticleDOI
New aeromagnetic and gravity compilations from Norway and adjacent areas: methods and applications
Odleiv Olesen,Marco Brönner,Jörg Ebbing,J. Gellein,Laurent Gernigon,J. Koziel,T. Lauritsen,Reidun Myklebust,Christophe Pascal,Morten Sand,D. Solheim,S. Usov +11 more
TL;DR: In the mid-1990s, the Geological Survey of Norway (NGU) produced new aeromagnetic and gravity maps from Norway and adjacent areas, compiled from ground, airborne and satellite data.
References
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Journal ArticleDOI
Gridding with continuous curvature splines in tension
Walter H. F. Smith,Paul Wessel +1 more
TL;DR: In this article, the authors proposed to add tension to the elastic-plate flexure equation to improve the convergence of a minimum curvature gridding algorithm with a tension parameter, where the same system of equations must be solved in either case and only the relative weights of the coefficients change.
Journal ArticleDOI
Machine contouring using minimum curvature
TL;DR: In this article, Finite difference equations are deduced from a principle of minimum total curvature, and an iterative method of solution is outlined, based on which the spline fit has well defined smoothness properties.
Journal ArticleDOI
A theoretical analysis of the properties of median filters
Neal C. Gallagher,G. Wise +1 more
TL;DR: In this article, the authors derived necessary and sufficient conditions for a signal to be invariant under a specific form of median filtering and proved that the form of successive median filtering of a signal (i.e., the filtered output is itself again filtered) eventually reduces the original signal to an invariant signal called a root signal.
Journal ArticleDOI
Simple micro-levelling for aeromagnetic data
TL;DR: In this paper, a simple technique is described for removing residual levelling errors from aeromagnetic data, which have a distinct spectral signature and are easily removed from a grid of the data.