Magnetometry refers to the measurement of magnetic fields and the magnetic properties of bodies. It is used as a geophysical prospecting method based on the systematic measurement of the Earth's magnetic field, at station points regularly distributed across the area of study. (source:

A magnetometer is an instrument designed to measure the direction and intensity of a magnetic field. The term "magnetic field" refers to the region of space around a magnet in which the magnetic forces are exerted. It also characterises the influence of an electric charge in motion and reciprocally exerts its action on the charges in motion. (source:

Examples of sensors

  • Proton Precession Geometrics G801 from 1981 to 1990
  • Proton Precession G866 from 1987 to 1990
  • Proton Precession Barringer M244 since 1990
  • Mag. Marine Magnetics Seaspy since 2001
  • Vector magnetometer Ixsea VM300D

More information on the website of the French oceanographic fleet.

File types

File type





Vector magnetometer - TECHSAS

Pourquoi pas ?


from 2006


Scalar magnetometer - TECHSAS

Pourquoi pas ? / Atalante


from 2006 (Pourquoi pas ?), 
 from 2008 (Atalante)


magnetism data processed

The Atalante, the Suroît, the Pourquoi pas ?




More information on file formats for geophysical data archived at SISMER

Magnetism data correction

  • Diurnal variation correction

The data are provided without correction of diurnal variations whether in the form of raw data or data converted to the international Marine Geophysical Data Exchange Format (MGD).

  • Calculation of magnetic anomalies

The measurements in Marine Geophysical Data Exchange Format (MGD) are provided with magnetic anomaly values calculated from the most recently published International Geomagnetic Reference Fields (IGRF) at the date of file creation.

For more information see the websites of International Union of Geodesy and Geophysics (IUGG) and NOAA.

  • Difference between the ship's position and the magnetometer's position

The raw data are not georeferenced. To do so we must:

    • interpolate the positions of measurements over time from the navigation file validated by Ifremer/Genavir
    • correct the position according to the length of magnetometer cable paid out. This length varies according to ships and the equipment used.


For all further enquiries, please contact the SISMER service (