Two topics in electromagnetic radiation field prospecting

Abstract: Different kinds of electrical methods have been used for a considerable time in the field of Applied Geophysics. In common these methods have almost exclusively been based on stationary or slow-varying electromagnetic fields. With a slow-varying field is meant a field whose wavelength is much larger than the characteristic dimensions of the body under study. That is, the field may be regarded as homogeneous in volumes of interest. In practice, a field with a frequency below let say 50 kHz may be regarded as slow~ varying. A certain class of electromagnetic fields is of the radiating type. In this case a considerable part of the electromagnetic energy will leave the near-zone of the transmitting antenna, and propagate as electromagnetic waves. In this dissertation, the author presents some of his research connected to electromagnetic radiation field prospecting carried out at the GeoPhysics Laboratory at Boliden Metall AB. In part 1 "Geophysical prospecting by radar" the possibilities in using HF, VHF and UHF frequencies are studied. These frequencies are found at the extreme high end of the electromagnetic spectrum, from a geophysical point of view. A particular interest is paid to the pulse-radar principle. In part 2 "New instrumentation for VLF radiation field prospecting" the technical details of the prospecting systems VLF-72/73 and WIMP-30 are presented. These systems utilize radiation fields at the extreme low end of the electromagnetic spectrum, in order to measure the apparent resistivity of the ground.