Locating & Detecting
A Magnetic Locator will find only ferrous metals, generally at greater depths.
The magnetic locator will not 'see' other types of metals and so will not be subject to signal interference from them - things like aluminum cans, pull tabs and other common "trash" materials found in many environments. Most ideal tool for the Surveyor.
For general ferrous, non ferrous, cavities, tunnel, pipes etc the use of metal detectors or geophysical scanners / locators can be used