How do magnetic observatories continuously record changes in Earth’s geomagnetic field?

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geomagnetic field The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.

Magnetic observatories continuously record changes in Earth’s geomagnetic field using both traditional and modern instrumentation.

Historically, observatories utilized magnetized needles suspended by quartz fibers, equipped with reflecting mirrors. Light beams reflected from these mirrors were imaged onto photographic negatives on rotating drums; these records, known as magnetograms, captured field variations as deflections on the negative.1

Most modern magnetic observatories have transitioned to electronic systems, typically housing proton-precession magnetometers and flux-gate magnetometers on granite pillars within temperature-controlled, nonmagnetic rooms. These instruments function as follows:1

Proton-precession magnetometers: Measure the magnitude of the field by detecting the precession frequency of protons in a fluid, which is dependent on the strength of the surrounding magnetic field.1
Flux-gate magnetometers: Measure the three components of the field vector by using sensors with high-permeability cores to detect even harmonics in a secondary voltage, which are proportional to the field component along the sensor axis.1

The electrical signals from these devices are digitized, recorded on magnetic media, and often transmitted to central facilities for storage in large computer databases.1