SOME PRACTICAL RESULTS OF AIRBORNE ELECTROMAGNETIC PROSPECTING IN SWEDEN*

In 1956 a total profile length of about 10,000 kilometers was surveyed in Sweden by a new airborne electromagnetic method. The purpose of the survey was to direct ground parties to areas where conducting ore bodies (sulphides etc.) might be found and to eliminate barren ground. In this method an electromagnetic rotating field is used and the variations in both the real and imaginary components of the applied field are measured. The airborne work can be done with one plane towing a bird on a long cable or with two planes without cable connection. The two‐plane method has proved to have definite advantages over other methods, as shown by practical examples. The relation between the magnitude of the anomaly over background noise in relation to the flying altitude and the transmitter‐receiver distance is demonstrated, as well as different types of anomalies obtained. The use of this airborne method for the mapping of shallow structures in oil field terrains is discussed.

The equipment for the ensuing electromagnetic ground investigations is briefly described and examples are given of anomalies obtained.