Abstract: A method and a device for implementing the method, for geophysical surveying of an area (1) including continuous measurement of the earth's magnetic and electromagnetic field using a detector (6) held at a constant height (E) above the ground surface, in the order of one meter, while traversing in a criss-cross manner over the area (1) at speeds below a maximum speed (S), in the order of 10 km/h, and utilizing measured signal frequencies below a cutoff (F), being approximately the maximum speed (S) divided by twice the detector height (E), to indicate spatial variations in the measured field. Traversal distance can be measured on board the host vehicle and a real time output supplied. Simultaneously, using the same detector (6) and artificially induced magnetic fields generated by an inductive (2b and/or galvanic source (2a)), temporally varying fields having frequencies above the cutoff (F) can be measured and simply filtered out of the detector's (6) output for separate processing and storage.