The Ørsted Satellite in the International Decade of Geopotential Field Research (Petrus Peregrinus Medal Lecture)

The launch of the Danish satellite Orsted on 23 February, 1999 marked the beginning of the “Decade of Geopotential Field Research”, an international effort to promote and coordinate a continuous monitoring of the geopotential (magnetic and gravity) field variability in the near-Earth environment. Already the first years of Orsted magnetic field observations showed that dramatic changes had taken place, in particular in the South Atlantic / South African continent during the 20 years that had elapsed without satellite data after the NASA MAGSAT satellite mapping of the Earth’s magnetic field.