Magnetic observatories and variometers
The magnetic field vector components are observed over many years at fixed observatories (some going back to the 19th century) around the world. The INTERMAGNET organisation sets standards and provides support to maintain a high quality global network of observatories. In addition to observatories, variometer stations provide measurements of the variations of the magnetic field. Though such measurements lack the accurate baselines that observatories provide, these data are valuable for monitoring fluctuations such as those due to space weather. The SuperMAG collaboration is a recent initiative to collate and provide access to variometer data in a consistent manner.
Measurements made at fixed locations are supplemented by a range of targeted surveys made by land, sea, and air. There are also a number of satellite missions providing high value data with global coverage.