The magnetic dipole moment of RV Alliance
A SACLANTCEN magnetometry sea trial was performed in September 1998 in the northern Tyrrhenian Sea in the vicinity of the Formiche di Grosseto islands. One of the trial objectivesconcerned the measurement of the magnetic dipole moment of the NATO research vessel Alliance with an array of fixed Ocean Bottom Magnetometers. The Alliance sailed with constant velocity alongthree specified tracks in reciprocating directions. The magnetic signature of the Alliance was subsequently extracted from the magnetic field data recorded during the experiment. From the magnetic signatures taken from six successive runs, quantitative magnetic dipole models were derived. A comparison between the magnetic signatures obtained from northwestward and southeastward runs yields estimates of the permanent and induced magnetic dipole moments in the horizontal plane. In the vertical direction, only the total magnetic dipole moment can be determined. The positions of the OBMs, uncertain to some extent, were fictitiously varied such that the horizontal components of the permanent magnetic dipole moment and the vertical component of the total dipole moment remained constant during the experiment. The induced horizontal dipole moment tended to increase steadily and monotonically in a northward direction. Explanations of this phenomenon arediscussed.