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

摘要

GEOSTAR, an European-funded project, is based on a submarine multidisciplinaryobservatory, that gathered geophysical and geochemical data during a period of sixmonths, from September 2000 to March 2001, in its first deep seafloor mission (about2000 m depth), off the coast of Ustica Island (Sicily, Italy). GEOSTAR was equippedwith several scientific instrumentations, among them two magnetometers. Totalintensity of the Earth’s magnetic field and its vectorial components were recorded bymeans of a scalar magnetometer (Overhauser type) and a suspended three axialfluxgate magnetometer, the latter being designed and built at the Istituto Nazionale diGeofisica e Vulcanologia laboratories. The adverse conditions of an environmentlocated at 2000 m under the sea surface, obliged the making of a special design for thewhole frame, including the use of non-magnetic materials for the structure, and theinstallation of two opposite expanding arms that contained the magnetometers. Thegeomagnetic experiment was completed by carrying out two fundamental procedures:the instrumental calibration and the computation of the vectorial magnetometerorientation 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 aspectral analysis performed in a particular condition of planetary magnetic activity, aswell as applications aimed at extracting information about the crustal electricconductivity from the magnetic data in the area around Ustica Island.