Abstract: An apparatus for detecting the presence of a buried, hidden object in the vicinity of a digging tool in order to prevent a human disaster and damage to utility lines or other buried structures. The apparatus includes an impulse generator and data processing means connected to a slot antenna formed in the tool of an earthmoving machine for radiating a burst of broad spectrum electromagnetic energy into the ground and for receiving and data processing reflected electromagnetic echoes. One antenna embodying the invention comprises a slot formed through a wall of a hydraulically driven shovel and filled with a ceramic absorber. The slot has four radially extending, orthogonally arranged loops having unclosed central portions of the loops joined end to end to form four apexes.