[18] Huge progress has been made in geomagnetism in the recent years thanks to magnetic data provided by the low-Earth orbiting satellites Ørsted and CHAMP, which were launched by Denmark and Germany, respectively. These satellites are like flying observatories, equipped with a fluxgate vector magnetometer and a Overhauser-type scalar magnetometer at the end of a boom of several meters length, in order to avoid electromagnetic disturbances from the spacecraft. Unlike ground observatories however, they are moving within the Earth's magnetic field, thus experiencing very different orientations of the field in only a couple of hours. This makes it possible to fully calibrate the vector magnetometer without absolute measurement, simply by minimizing the scalar residual [Olsen et al., 2003].
[19] Magnetic satellites have a quasi-circular, quasi-polar orbit at low altitude (around 700 km for Ørsted, 450 km for CHAMP), so that they provide a global and homogeneous coverage of the Earth's internal magnetic field after orbiting a few days only. Moreover, they slowly drift in local time, which is very useful for studying external field variations. These properties, together with the prospect of the upcoming ESA Earth Explorer Mission Swarm [Friis-Christensen, 2006] to be launched in 2010, have raised the question of whether magnetic observatories will still be useful and relevant to societal concern in the future [Kerridge, 2007]. This may seem a bit odd, at a time when about 100 scientific publications relying directly or indirectly on observatory data are published every year in major geophysics journal [Newitt, 2007]. In fact, satellite and observatory data are complementary for many applications, such as separating the various sources in geomagnetic field models, because they have different spatio-temporal properties: observatories are fixed points below the ionosphere, while satellites are moving points above the ionosphere. Observatory data are also used to validate satellite data (and conversely) and they are the only data available for global modeling in years in between satellite missions, such as 2010 for example. Moreover, observatories remain the only source of data for studying the long-term evolution of the ionospheric and magnetospheric magnetic fields [Chulliat et al., 2005], as well as solar activity [Svalgaard and Cliver, 2007].
[20] The growing concern for global change and the advent of magnetic satellites bring new challenges and opportunities for magnetic observatories. In order to meet those challenges, INTERMAGNET recommends to increase the sampling frequency of vector data up to 1 Hz, in order to be synchronized with magnetic satellite data, and also to address the growing demand from the space physics community to have one-second magnetic data at the global scale for studying ULF waves in the ionosphere and magnetosphere. This upgrade will be done in the near future at the Borok INTERMAGNET observatory.
Powered by TeXWeb (Win32, v.2.0).