[1] There are various geophysical techniques for forensic investigations in which the targets are buried and have different dimensions (from weapons or metallic barrels to human burials and bunkers).
[3] For large-scale buried objects, seismic surveys may be appropriate but these have, at best, 2m vertical resolution so may not be ideal for certain targets, more typically they are used to detect bedrock below the surface.
There are different equipment configurations, the dipole-dipole (fixed-offset) method is the most common which can traverse across an area, measuring resistivity variations at a set depth (typically 1-2x probe separations) which have been used in forensic searches.
More slower methods are putting out many probes and collecting both spatially horizontally and vertically, called Electrical resistivity imaging (ERI).
There has been recent efforts to undertake research over known buried and below-water surface simulated forensic targets in order to gain an insight into optimum search technique(s) and/or equipment configuration(s).