World Digital Magnetic Anomaly Map

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The World Digital Magnetic Anomaly Map (WDMAM) was first made available by the Commission for the Geological Map of the World in 2007. Compiled with data from governments and institutes, [1] the project was coordinated by the International Association of Geomagnetism and Aeronomy, and was presented by Mike Purucker of NASA and Colin Reeves of the Netherlands. [2] As of 2007, it was considered to be "the first truly global compilation of lithospheric magnetic field observations." and further improvements dated to 2009 relate to the full spectrum magnetic anomaly grid of the United States and also data of global marine magnetic anomaly. [3]

Contents

Some of the magnetic anomalies shown in the WDMAM generally relates to the altitude level of 5 kilometres (3.1 mi). Some of the significant features represented are of the Bangui Anomaly in the Central African Republic, the Chicxulub crater, the Thromsberg anomaly, the Richat Structure, the Atlantic ridge, the Bay of Biscay, the Sunda Arc and the Paris Basin. [4]

Background

WDMAM v1, 2007

In evolving the WDMAM the lithospheric data related to data acquired from satellites, data of aero-magnetic survey and marine survey, in-situ data gathered from field stations and observatories are to be collated analyzed together, and this would need an international joint effort. [5]

The map is the product of years of work, research and coordination by the International Association of Geomagnetism and Aeronomy (IAGA) and numerous small organizations around the world including GETECH, a project of Leeds University, and Juha Korhonen of the Geological Survey of Finland have also been involved. [6] International collaboration has been the key to the project. Mike Purucker of NASA said of the collaboration: "There are literally hundreds, perhaps thousands, of organisations around the world which hold this kind of data. One should not underestimate the diplomatic efforts needed to secure support and data contributions from these organizations." [6] Diplomacy was needed to acquire data from the Russians, Indians, and Argentinians and so on. [6] It is available through the Commission for the Geological Map of the World.

The map is compiled from a jigsaw of aeromagnetic surveys, incorporating both ground-based, airborne and marine magnetic data, but is incomplete. [7] [8] CHAMP, a German and Russian-built satellite which has been in orbit since 2001, has been of crucial importance to the map compilers. [6] One of its principal achievements is that it has significantly improved the "pre-processing and the corrections applied to the CHAMP satellite measurements in order to obtain 'clean' satellite data compatible with ground data." [9] However, it has some large gaps in data, which is a hindrance to studying trans-national tectonics, and could benefit from further satellite observational additions to improve its coverage. [7] [10]

Several different models were put forward as candidates for WDMAM by groups from NASA, Leeds University, the Geological Survey of Finland, National Geophysical Data Center (NGDC) and GeoForschungszentrum Potsdam, all using the same base data. [11] Following a review, the NGDC candidate was chosen to form the basemap. [12]

Specified to a grid of three arcminutes, the WDMAM v1 was based on the NGDC's EMAG3 (Earth Magnetic Anomaly Grid, 3 arcminute) dataset. The EMAG has since been improved into EMAG2 at a resolution of two arcminutes and fitted into the Enhanced Magnetic Model.

WDMAM v2, 2015

Composition

According to the BBC, the "global map shows the variation in strength of the magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000 nano- Tesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks." [6] The map is graphically represented by illustrating those landmarks of high magnetism in red to yellow hues and those of lower or negative magnetism in blue hues. [6] It can pick up numerous aspects of the earth composition, including the sea floor spreading under the oceans, and reserve deposits like iron ore at Kursk. [6] It identifies some prominent magnetic anomalies on the African continent. [13] The dominant factors for magnetic anomalies picked up on the map are "the thickness of the magnetised layer and the composition of the crust". [6] Younger crust is typically thinner, and naturally has a lower number of magnetic materials. [6]

Related Research Articles

<span class="mw-page-title-main">Geophysics</span> Physics of the Earth and its vicinity

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<span class="mw-page-title-main">South Atlantic Anomaly</span> Region where Earths magnetic field is weakest relative to an idealised dipole

The South Atlantic Anomaly (SAA) is an area where Earth's inner Van Allen radiation belt comes closest to Earth's surface, dipping down to an altitude of 200 kilometres (120 mi). This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher-than-usual levels of ionizing radiation.

<span class="mw-page-title-main">Earth's magnetic field</span> Magnetic field that extends from the Earths outer and inner core to where it meets the solar wind

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.

<span class="mw-page-title-main">Polar drift</span> Geological phenomenon resulting in shifts in the magnetic poles

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A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons.

<span class="mw-page-title-main">Aeromagnetic survey</span> Surveying method, analyzing the magnetic properties of large regions from high altitudes

An aeromagnetic survey is a common type of geophysical survey carried out using a magnetometer aboard or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger areas of the Earth's surface to be covered quickly for regional reconnaissance. The aircraft typically flies in a grid-like pattern with height and line spacing determining the resolution of the data.

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The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey. The data and updates are issued by the US National Geospatial Intelligence Agency and the UK Defence Geographic Centre.

<span class="mw-page-title-main">Magnetic anomaly</span> Local variation in the Earths magnetic field

In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying material. The magnetic variation in successive bands of ocean floor parallel with mid-ocean ridges was important evidence for seafloor spreading, a concept central to the theory of plate tectonics.

<span class="mw-page-title-main">Earth science</span> Fields of natural science related to Earth

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<span class="mw-page-title-main">North magnetic pole</span> Earths magnetic pole in the Northern Hemisphere

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<span class="mw-page-title-main">South magnetic pole</span> Point on Earths Southern Hemisphere

The south magnetic pole, also known as the magnetic south pole, is the point on Earth's Southern Hemisphere where the geomagnetic field lines are directed perpendicular to the nominal surface. The Geomagnetic South Pole, a related point, is the south pole of an ideal dipole model of the Earth's magnetic field that most closely fits the Earth's actual magnetic field.

<span class="mw-page-title-main">Geomagnetic pole</span> Poles of a dipole approximation to the Earths field

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<span class="mw-page-title-main">Bangui magnetic anomaly</span> Local variation of the Earths magnetic field in central Africa

The Bangui magnetic anomaly is a local variation in the Earth's magnetic field centered at Bangui, the capital of Central African Republic. The magnetic anomaly is roughly elliptical, about 700 km × 1,000 km, and covers most of the country, making it one of the "largest and most intense crustal magnetic anomalies on the African continent". The anomaly was discovered in the late 1950s, explored in the 1970s, and named in 1982. Its origin remains unclear.

Kathryn Anne "Kathy" Whaler OBE FRSE FAGU is a professor of geophysics at the University of Edinburgh School of GeoSciences, in the Research Institute of Earth and Planetary Science and is a member of the Solid Earth Geophysics and Natural Hazards Research Group.

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<span class="mw-page-title-main">Indian Institute of Geomagnetism</span>

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<span class="mw-page-title-main">Crustal magnetism</span>

Crustal magnetism is the magnetic field of the crust of a planetary body. The crustal magnetism of Earth has been studied; in particular, various magnetic crustal anomalies have been studied. Two examples of crustal magnetic anomalies on Earth that have been studied in the Americas are the Brunswick magnetic anomaly (BMA) and East Coast magnetic anomaly (ECMA). Also, there can be a correlation between physical geological features and certain readings from crustal magnetism on Earth. Below the surface of the Earth, the crustal magnetism is lost because the temperature rises above the curie temperature of the materials producing the field.

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References

  1. ↑ Seward, Liz (November 2, 2007). "Digital magnetic map goes global". BBC.
  2. ↑ Preview. Australian Society of Exploration Geophysicists. 2007. p. 16. Retrieved 12 April 2013.
  3. ↑ Mandea, M.; Korte, Monika (2011). Geomagnetic observations and models. Springer. p. 312. ISBN   978-90-481-9858-0 . Retrieved 12 April 2013.
  4. ↑ Flechtner 2010, p. 518.
  5. ↑ Flechtner 2010, p. 514.
  6. 1 2 3 4 5 6 7 8 9 "Digital magnetic map goes global". BBC News. 2 November 2007. Retrieved 12 April 2013.
  7. 1 2 Mozzoni, David T. (2007). The Changing Geomagnetic Field from the Ionosphere to the Core-mantle Boundary. p. 22. ISBN   978-0-549-46723-6 . Retrieved 12 April 2013.
  8. ↑ Anderson, Jarod E. (2009). The lithosphere: geochemistry, geology and geophysics. Nova Science Publishers. p. 331. ISBN   978-1-60456-903-2 . Retrieved 12 April 2013.
  9. ↑ Glassmeier, Karl-Heinz; Negendank, Jörg F. W.; Soffel, Heinrich (2006). International Final Colloquium of the German Science Foundation Priority Programme 1097: "Geomagnetic field variations: space-time structure, processes, and effects on system earth" ; October 4 - 5, 2006 Braunschweig, Germany. GeoUnion Alfred-Wegener-Stiftlung. p. 63. Retrieved 12 April 2013.
  10. ↑ Committee to Review NASA's Solid-Earth Science Strategy; National Research Council (31 December 2004). Review of NASA's Solid-Earth Science Strategy. National Academies Press. p. 20. ISBN   978-0-309-16571-6 . Retrieved 12 April 2013.
  11. ↑ Encyclopedia of Solid Earth Geophysics. Springer. 29 June 2011. p. 809. ISBN   978-90-481-8701-0 . Retrieved 12 April 2013.
  12. ↑ Maus S, Sazonova T, Hemant K, Fairhead JD, Ravat D (2007). "National Geophysical Data Center candidate for the World Digital Magnetic Anomaly Map" (PDF). Geochemistry, Geophysics, Geosystems. 8 (Q06017). Bibcode:2007GGG.....8.6017M. doi: 10.1029/2007GC001643 .
  13. ↑ Hüttl, Reinhard F. J. (1 August 2011). Ein Planet voller Überraschungen / Our Surprising Planet: Neue Einblicke in das System Erde / New Insights into System Earth. Springer. p. 151. ISBN   978-3-8274-2470-9 . Retrieved 12 April 2013.

Bibliography

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