Simplified Interpretation of Turam Anomalies

The Turam electromagnetic (EM) method employs the fixed transmitter/moving receiver system in which the ratio of the amplitudes of the electromagneti c field at sets of two poi nts and the phase differences between the points are measured. For a given transmitter these quantities will v ary from theoretical values in a homogeneous half space only when secondary sources or conductors are present. Deri vation of the parameters of conductors detected by the method has in the past, relied on the computation of the real (in phase) and imaginary (out of phase) components of the resultant E.M, field. This paper shows that depth to the secondary sources which behave as line conductors can be estimated directly from the ratio and phase curves as accurately as from the real and imagi nary components.

It is also shown, that, for the reduced ratio (RR) over the top of the secondary source, and the corresponding phase angle di fference (θ),

where Φ is the phase lag between the primary signal and the induced secondary signal. This expression, the Phase Lag Function, is equivalent to the Apparent Induction Index, which has been used to determine the resistivity/thickness ratio of a conductor.

Nomograms relating the Phase Lag Function to the resistivity/thickness ratio for various bodies are provided so that all routine interpretation of Turam anomalies can be performed on the ratio and phase curves.