A magnetic survey is a geophysical method used to measure variations in the Earth's magnetic field. This technique helps identify subsurface geological features, such as mineral deposits or archaeological sites, by detecting changes in magnetic intensity caused by different materials. During a magnetic survey, instruments like magnetometers are used to collect data over a specific area. The results can reveal important information about the Earth's crust and assist in resource exploration, environmental studies, and even archaeology. This non-invasive method is valuable for mapping and understanding the Earth's structure without the need for drilling.