The magnetometers and the geomagnetic data from GEOSTAR, a deep seafloor multidisciplinary observatory

GEOSTAR, an European-funded project, is based on a submarine multidisciplinary observatory, that gathered geophysical and geochemical data during a period of six months, from September 2000 to March 2001, in its first deep seafloor mission (about 2000 m depth), off the coast of Ustica Island (Sicily, Italy). GEOSTAR was equipped with several scientific instrumentations, among them two magnetometers. Total intensity of the Earth�s magnetic field and its vectorial components were recorded by means of a scalar magnetometer (Overhauser type) and a suspended three axial fluxgate magnetometer, the latter being designed and built at the Istituto Nazionale di Geofisica e Vulcanologia laboratories. The adverse conditions of an environment located at 2000 m under the sea surface, obliged the making of a special design for the whole frame, including the use of non-magnetic materials for the structure, and the installation of two opposite expanding arms that contained the magnetometers. The geomagnetic experiment was completed by carrying out two fundamental procedures: the instrumental calibration and the computation of the vectorial magnetometer orientation with respect to the geographical reference, both are described in this paper. We also illustrate some properties of the complete magnetic data set, together with a spectral analysis performed in a particular condition of planetary magnetic activity, as well as applications aimed at extracting information about the crustal electric conductivity from the magnetic data in the area around Ustica Island.