Geomagnetic reference fields and direction-finding applications

Regional models of the geomagnetic field offer higher resolution than can be achieved with global models. However, for any particular application, the choice of geomagnetic reference field, global or regional, depends on the accuracy requirements and whether information at crustal wavelengths is needed. The most stringent demands of directional drilling may be beyond the accuracy limits of even the best regional models, whereas a good global model may be adequate to meet many navigational requirements. Accurate regional data, particularly estimates of secular variation from observatories and repeat stations, provide the foundations for global as well as regional field models, and need to be made available to the world community.