Fast calculation of theoretical response curves for induction depth sounding

A quasi-analytical method is presented for efficiently evaluating the integral expression for the magnetic field (MF) vertical component generated on the surface of a layered earth structure by exposure to an induction depth sounding loop source. The radial distribution of the vertical MF is expressed in closed-form as a linear combination of Hankel functions. The field strength versus induction number is calculated assuming a two-layer earth model. The obtained results are in good agreement with the ones provided by the commonly used digital filter algorithms.