An apparatus for reducing rotation of an article such as a bird for holding a superconducting quantum interference device for use in airborne transient electromagnetic mineral prospecting. The apparatus includes a support sphere having an inner shell and an outer shell. Liquid is contained between the inner and outer shells and a sphere has openings through which support strings project for locking to an internal point within the sphere. The strings have one end connected to an internal point within the support sphere and another end connected to a spring. The spring includes a damper for damping movement of the spring. Baffles are arranged in the cavity between the inner and outer shells in which the liquid is contained for damping movement of the liquid.

A towed aircraft for use in an airborne electromagnetic geophysical prospecting system which includes a transmitting antenna and power generating means for powering the antenna. A bird to which is mounted a receiving antenna may be towed by the towed aircraft.

The invention is predicated upon the fact that a buried object causes a disturbance of the local value of the earths magnetic field due to both the disruption of the soil and the material of the object. The change in intensity of the field will usually be to small to detect reliably, but the horizontal and/or vertical gradients of the magnetic disturbance is detectable. A method of detecting a localized disturbance of the ground is disclosed in which a plurality of mutually spaced apart detector units are swept across an area of ground suspected of containing a localized disturbance and in which the detector units are responsive to the magnetic field gradient associated with the resulting disturbance of the load magnetic field. Non-metallic objects may be detected.

A conductivity anomaly detection system uses a rotating superconducting met to generate a known source field and an integrated detection system rotating with the superconducting magnet to detect anomalies in the generated source field caused by nearby conducting targets. The superconducting magnet is rigidly mounted in a Dewar which is in turn mounted on a shaft. An orthogonal detection system also is rigidly mounted on or within the Dewar with the superconducting magnet. The second harmonic of the anomaly signal from a target is detected for signal processing.

A prospecting system uses a rotating superconducting electromagnetic source which is swept over a frequency range with a magnetometer type receiver sensing the induced field. The effective dipole is rotated in a horizontal plane parallel to the ground surface with the sensed induced magnetic field being in the vertical axis.