HTS dc SQUID systems for geophysical prospection

We describe the use of high T/sub c/ flip-chip dc SQUID magnetometers in systems for several geophysical prospection methods. For use in the Transient Electro Magnetics (TEM) method, a one-channel SQUID magnetometer system (vertical field component) was adapted to rough conditions in the field. We report on measurements in South Africa over a geophysically interesting target in real production mode. Transients up to 200 ms could be recorded, which is about a factor of 100 more than with conventional coils. For investigation of the magnetic field gradient a two-channel system, built as a first-order electronic gradiometer with a baseline up to 1 m, was designed and manufactured. It can be used, e.g., for surface exploration or for archeometry. The system can be moved in the Earth's magnetic field. We achieve a common mode rejection of 100. The reasons for the imbalance and the possibility of further improvement of the system are discussed.