Geometrics, a leader in geophysical equipment,
offers a classic well written document about how to conduct a magnetometer survey. Click here to read APPLICATIONS MANUAL FOR PORTABLE MAGNETOMETERS (6.4Mb). The document provides geophysicists, engineers, scientists, and other professionals insight on magnetic theory and survey design. Magnetic fields are often elusive to people conducting magnetic surveys because magnetic fields are not visible to the naked eye. While having intimate knowledge about magnetic theory is always beneficial, it is often difficult to embrace.
Geometrics says “This Manual was written to satisfy most of the needs of the average user of a portable total field magnetometer for both conventional and unconventional applications, including geological exploration, search for lost objects, magnetic measurements of rock or iron specimens and archaeological prospecting. As the name implies, this is a manual or guide for professional and non-professional persons who may not have the time, the requisite background or the ready access to the proper libraries to delve deeply into standard texts, the few that there are, on applied geophysics.”
The document introduces the reader to magnetometers, the earth’s field magnetism, field procedures, interpretation, theory, magnetic search, gradiometers and gradient techniques, and magnetic measurements of electric current distributions. Since the introduction of this manual, cesium vapor magnetometers (e.g. G-858 and G-859) have become readily available. The new technology allows magnetometer data to be collected at rates of ten readings per second. With high data acquisition rates it is feasible to tow the unit on a non-magnetic cart. Systems are designed to acquire horizontal and vertical gradients. Operators can integrate global positioning systems GPS with the magnetometers to avoid setting up detailed grids. However, one should be aware that the positioning of the the magnetic data will only be as good as the accuracy and repeatability of the GPS data. This issue becomes a much larger problem as the target size gets smaller. Inexpensive consumer grade GPS data would likely work for finding an ore deposit. However, locating a gun or an ordnance may require centimeter accuracy, which is only available through higher end GPS systems.