Technique of Magnetic Measurements

Any form of data whether acquired at an observatory or through experiments concerning studies of space and solid Earth described in this book, need instruments. These instruments, essentially magnetometers, are distinguished not only by the component of the field they measure, but also by the principle of their working. The principles employed in magnetometers range from the elementary laws of forces acting on a magnetic needle, to the technique of optical pumping. There are different types of magnetometers, which include theodolite magnetometers, torsion magnetometers, variometers, Lloyd’s and Schmidt’s balances and Earth inductors. The recent additions are the nuclear magnetic resonance magnetometers, saturable-core magnetometers (fluxgate magnetometers), induction magnetometers and more. The magnetometers introduced in the late twentieth century include proton precession magnetometers (PPM), optical pumped sensors, super quantum interference devices (Squids) and others. The most important change in instrumentation in the last half-century, however, is the automation of observation and the direct connection of sensors to data storage and computational facilities. This chapter outlines the importance and use of three categories of instruments in magnetic measurements: magnetic observatories, ground and marine magnetic surveys and laboratory magnetometers. Some “current” instruments are also included in these three categories of magnetic measurements.