Abstract:

The authors introduce a method to generalize the computation of Green’s functions from primary sources buried in stratified earths. A fictitious interface paralleling to layer interfaces through source is inserted. This new interface makes all the electromagnetic vector potentials, which can be split into TE and TM modes, satisfy homogeneous Helmholtz equations, with up-and down-going wave functions as the solutions. The amplitudes of wave functions in any layer could be recursively calculated from the initial amplitudes in the layers bounding the fictitious interface, while the initial amplitudes can be related with the discontinuity of tangential electric field and continuity of tangential magnetic fields on the fictitious interface.The Green’s function in standard Hankel transform, transformed from these potentials, can then be estimated. The methodology was applied to calculating the E and H field from VED source in marine electromagnetic exploration. Numerical results demonstrate the feasibility and accuracy of the formulation.

Key words: marine electromagnetic method, 1-D model, Green’s function, source contained boundary condition, fictitious interface