4.3 Magnetic Observatory Distribution

It should be noted that the global models such as BGGM and even HDGM, can only measure longer wave length effects of the Earth’s magnetic field distribution and cannot be expected to take account of very localised crustal effects caused by magnetic minerals, typically found in deep basement formations in the vicinity of drilling. See other chapter for a discussion of In Field Referencing (IFR), a technique for measuring the local field to a higher accuracy.