Question: how do you know whats going on under the ground?

Jamie Pringle answered on 11 Mar 2011:

Generally I am involved in looking for things buried in the top 10 metres below the ground surface. If there is a physical contrast between what I am looking for (the target) and the rest of the site (the background), then I should be able to find it. For example, if I am looking for a buried knife in a rural field, then if I do a magnetics survey to find buried metal (using a device like a high tech metal detector), then I should find an anomalous area within the site and tell the investigators to go and dig there! However, if I am looking for the knife in a scrapyard, then I would be stuffed as the whole site would be full of metal and there would be no point in doing a magnetics survey.

Other instruments, particularly ground penetrating radar, can tell you WHERE things are under the ground surface and more importantly HOW far down they are, which is really helpful to the guys digging things up!