French Repeat Station Survey
What is it?
Geomagnetic repeat stations are defined locations within a certain region (usually a country) where absolute measurements are carried out in regular time intervals, usually annually to once every 5 years. Repeat station data are used to map the main field and study secular variation in detail. The French National Observatory (CLF) is responsible for the French repeat station measurements.
How is it made?
The French geomagnetic repeat station network currently consists of 32 points out of a denser network from former ground vector surveys. Regular repeat station surveys started in 1948 and were carried out every 5 years. The measurements are taken by a fluxgate theodolite (D, I) and a proton magnetometer (F). Here is the 2007 map:
