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Location: UFOUpDatesList.Com > 2007 > Nov > Nov 29

Digital Magnetic Map Goes Global

From: Sergey Shpakovsky <sergejsh.nul>
Date: Wed, 28 Nov 2007 11:51:05 -0800 (PST)
Archived: Thu, 29 Nov 2007 06:47:11 -0500
Subject: Digital Magnetic Map Goes Global

Source: BBC News - London, UK


Friday, 2 November 2007

Digital Magnetic Map Goes Global

The first global map of magnetic peculiarities - or anomalies -
 on Earth has been assembled by an international team of

Magnetic anomalies are caused by differences in the
magnetisation of the rocks in the Earth's crust. Many years of
negotiation were required to obtain confidential data from
governments and institutes. Scientists hope to use the map to
learn more about the geological composition of our planet.

The World Digital Magnetic Anomaly Map (WDMAM) is available
through the Commission for the Geological Map of the World.

The magnetic signature of the Earth's crust has been measured
for many decades by a multitude of groups; but now, for the
first time, the data has been combined to give a truly worldwide
view of the phenomenon.

See map in detail:


A British company involved in the project is GETECH, a spin-off
from Leeds University.

Valuable tool

Managing Director Dr J Derek Fairhead explains: "The project is
the result of a lot of coordinating efforts by the IAGA
(International Association of Geomagnetism and Aeronomy)
organisation to put together a magnetic map of the world, and
it's taken decades to get to this position.

"Many of the companies and country organisations who hold the
data in a confidential mode have been prepared to release
'decimated versions' of their data so that the commerciality of
the data isn't affected.

"But the regional nature of the magnetic field can be clearly
imaged and put together with all the other data to generate a
global image of the magnetics."

The Kursk Magnetic Anomaly: http://tinyurl.com/326pan

Dr Juha Korhonen, one of the lead researchers on the project
from the Geological Survey of Finland, explained that the map
was available at "a low resolution".

 "It represents a square grid of about five kilometres, so it's
very coarse indeed. It is a starting point, and to go into
detail, you can contact those organisations who have more
detailed data on both the geology and mineral sources.

The Earth's magnetic rocks - PDF 4.2 MB:

"There are just a few major deposits that can be seen on this
map, like the Kursk iron ore deposit. Mainly one can see the
major geological formations.

"It's generally considered in prospecting and resource analysis
that this magnetic anomaly field is one of the most valuable
tools or regional assets."

Many causes

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 nanoTesla (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.

Hot colours (reds) indicate high values; cold colours (blues)
indicate low or negative values.

The map shows up how the sea floor spreads apart in mid-ocean:


As well as revealing ore deposits, magnetic anomalies can also
show areas of ground water and sea weakness zones. It is a
useful tool for geologists and geophysics, as well as a teaching

The information can be viewed as a flat, two-dimensional map or
rendered in 3D on a virtual globe.

There are several different causes of magnetic anomalies in the
Earth's crust.

On the ocean sea bed, the map shows a striped effect. Where
Earth's tectonic plates are moving apart, new crust is created
at mid-ocean ridges.

As the new material spreads out and cools, minerals in the rocks
that make up the crust are magnetised in the direction of the
Earth's magnetic field at the time of their formation. This
field reverses polarity over time, creating alternating stripes
on either side of the ridge.

On land, the dominant factors for magnetic anomalies are the
thickness of the magnetised layer and the composition of the
crust. Usually, young crust is relatively thin and has a low
content in magnetic minerals.

The old cratons, stable interior sections of the continental
crust, are thicker and have high magnetic mineral content.
Perhaps the most prominent feature is the Kursk anomaly, which
can be seen at the border between young western Europe and the
old "Baltic Shield".

First identified in the late 18th Century, the anomalous region
became the focus of a major industrial effort by the Soviets to
develop iron ore mines.

Pieces in a jigsaw

The international team had many difficulties to overcome in
creating its map.

Dr Korhonen said: "To acquire the Russian data required a
ministry decision there. Then India released their data. We have
Argentine data, similarly, which has been closed to all the

Dr Michael Purucker from the US space agency (Nasa), a user of
the map, said: "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 organisations."

One of the challenges in gathering data from many different
sources is piecing it together, and ensuring that all the data
sets are in the same format.

"There are different techniques," explained Dr Korhonen. "If the
techniques are somewhat similar, it's fairly easy finally doing
the calculations in a similar fashion to put the map together.

"If the anomaly is defined in some other way, then we might have
[a] problem. That's the main reason that the long wavelengths
have been removed from the ground-based data and replaced by
satellite data."

Next steps

This magnetic data has been gathered by Champ, a German and
Russian-built satellite that has been in orbit since 2001. Now
coming to the end of its life, it has charted the entire globe.

Not only does Champ measure the Earth's magnetic field, it can
also measure the very long wavelength components of the Earth's
crustal field with wavelengths greater than about 400 km, said
Dr Fairhead.

With the publication of the first edition of the map, the team
is already planning the second edition.

One area it hopes to improve on is the marine data coverage. The
first edition uses information from the US National Geophysical
Data Center, but there are other sources that may help to
improve the accuracy of the map.

The upcoming Swarm magnetic field satellites, to be flown by the
European Space Agency (Esa), will also help build new detail
into the map.

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