What is the BCMT?

The “Bureau Central de Magnétisme Terrestre” (BCMT) is in charge of organizing and coordinating the French observations of the Earth’s magnetic field. It was founded by a decree in 1921 and attached to the Institut de Physique du Globe de Paris (IPGP). Two French institutions are involved in BCMT operations: IPGP and École et Observatoire des Sciences de la Terre (EOST). These two institutions exchange their knowledge and coordinate their actions. Each institution is responsible for its own observatory network. In 2008, the Institut National des Sciences de l’Univers (CNRS-INSU) certified the BCMT as one of the National Observation Service in Magnetism. The main advisory body of the BCMT is its Scientific Council, set up in 2009.

Today, the BCMT operates:

• the National Magnetic Observatory, located in Chambon-la-Forêt (Loiret, France), about 100 km south of Paris, where the Earth’s magnetic field has been continuously recorded since 1936, following earlier recordings at two other locations in the Paris area (Parc St Maur, 1883-1900, and Val Joyeux, 1901-1935);
• a network of 16 overseas observatories, including 10 observatories in cooperation with foreign institutions;
• a network of 11 repeat stations in metropolitan France.

Sixteen BCMT observatories belong to INTERMAGNET, the global network of magnetic observatories transmitting their data in near real time and fulfilling high quality standards. This represents about 15% of the total INTERMAGNET network.

The BCMT distributes raw magnetic measurements as well as various data products derived from these measurements on its website and on the INTERMAGNET website.

In addition, the BCMT develops, builds and calibrates its own lines of vector and scalar magnetometers, providing significant flexibility to its operations.

Absolute pavilions (left) and magnetometer vault (right) at the Chambon-la-Forêt
magnetic observatory.