The effect of loop height in transient electromagnetic modelling or prospecting

Abstract

The voltage induced in a horizontal loop over a uniform ground at height, h, has been calculated for the case where the loop is excited by a step current. If the loop has a radius b and the ground has a permeability of m and conductivity then at time t: [see full text for equation]. For smb2/(4t) in the range 10?4 to 1 the maximum error in using this formula is less than 44%. If is less than 0.1 the error is less than 5%. It is suggested, then, that for small h, [see full text for equation] and that the above formulae will give first order corrections for the voltage induced in the loop for changes in elevation of the loop.