NLAYER: An ELFE Code for Horizontally Stratified Media (NLAYER: En ELFE-Kod foer211 Horisontellt Skiktade Medier)

摘要

NLAYER is a program written in FORTRAN 77 for the computation of ELFE (extremely211u001elow frequency electromagnetics) fields from monofrequent dipole sources in 211u001ecylindrical geometries with an arbitrary number of horizontal homogenous layers. 211u001eThe field components are obtained by numerical integration of 1D Sommerfield 211u001eintegrals in the wave number region. The principal problem is to perform a fast 211u001eand accurate computation of the integrands in these integrals. Roughly, the 211u001eintegrands are products of two factors, one dependent on the lateral distance 211u001efrom the source and the other on the depth coordinate. For multilayered problems 211u001ethe computation of the depth-dependent factor is the most time-consuming part 211u001esince it requires the solution of a system of equations in which the number of 211u001eunknowns are proportional to the number of layers. The new approach in NLAYER is 211u001eto do this evaluation only at a few adaptively selected radial wavenumbers. In 211u001ethis process the derivative is also extracted, which enables the use of cubic 211u001eHermite interpolation for values in between.