Variations of the Earth’s magnetic field with times of several years or more reflect the processes within the planet and cause great scientific interest. Over the past 100 years the regular observations at magnetic observatories (MOs) and repeat stations are the only experimental basis for studying such variations. In recent decades, satellite measurements have complemented ground-based measurements, thus partially solving the problems of spatially highly heterogeneous global network of magnetic observatories. Absolute observations are made at MOs to get the total field intensity vector. Until now, these measurements are performed manually, they are labor intensity and subject to many factors, that are often poorly controlled and reduce the reliability of the results, especially over long periods of time (years and decades), including (1) systematic errors of used magnetometers; (2) magnetic pollution of the absolute pavilion and its surroundings (at a distance of the first hundred meters); (3) instability of the pillars and remote target required to determine magnetic declination; (4) changes of observers and their weak qualification. Significant methodological problems arise if MO is moved to new location without special activity or infrastructure of MO (pavilions or pillars) is changed without careful control. For long-term stability and reliability of measurements, magnetic observatories were joined in IAGA network and then INTERMAGNET. Within these networks, requirements and standards have been defined, absolute magnetometers are compared every two years and observers are being trained. Modern hardware technologies allow to solve partially problems the automation of absolute observations, the self-calibration of the magnetometers, the checking of the MO’s magnetic environment, etc. Fully automated measurement systems help to expand the MO network.
Long-term changes in solar quiet (Sq) geomagnetic variations related to Earth's magnetic field secular variation
