Magnetic model of the earth unveiled

October 29, 1999

A Danish satellite launched in February has produced the first accurate map of the Earth's magnetic field for 20 years.

The satellite - which is named after Hans Christian Orsted (1777-1851), a Danish physicist who discovered the magnetic effect produced by an electric current - has provided almost 14,000 measurements for a new magnetic field model that has been adopted by the International Association of Geomagnetism and Aeronomy (IAGA).

The model will ensure greater accuracy in calibrating navigational equipment and researching processes in the earth's core.

It was prepared by scientists at the Nasa Goddard Space Flight Center, the Niels Bohr Institute of the University of Copenhagen and the Orsted Scientific Data Centre of the Danish Meteorological Institute, under the leadership of Nils Olsen of the Danish Space Research Institute (DSRI).

"A new model is necessary because the magnetic field is constantly changing and the magnetic poles are not stationary," said DSRI director Eigil Friis Christensen.

"Earlier models were based on measurements from about 100 magnetic observations around the world. They were unevenly distributed and there was little data from the oceans. Only satellite measurements can give global coverage," he continued.

"The present satellite measurements date from Nasa's Magsat 20 years ago. That model is becoming increasingly inaccurate, and people who use it must make many corrections. Much research connected with understanding the processes in the Earth's centre cannot be done because those measurements are no longer good enough."

According to Friis-Christensen, "a correct model of the Earth's magnetic field cannot be made simply from observations of the size of the magnetic field. Its direction is also necessary. This is one of the difficulties in magnetic mapping. But Orsted - which has a special camera that uses the stars to calculate the satellite's position accurately - has also solved this problem."

The new IAGA model, International Geomagnetic Reference Field 2000, is valid from January 1 for five years.

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