We have constructed a forward modelling code in Matlab, capable of
handling several commonly used electrical and electromagnetic methods
in a 1D environment. We review the implemented electromagnetic field
equations for grounded wires, frequency and transient soundings and
present new solutions in the case of a non-magnetic first layer.
The CR1Dmod code evaluates the Hankel transforms occurring in the
field equations using either the Fast Hankel Transform based on digital
filter theory, or a numerical integration scheme applied between
the zeros of the Bessel function. A graphical user interface allows
easy construction of 1D models and control of the parameters. Modelling
results are in agreement with other authors, but the time of computation
is less efficient than other available codes. Nevertheless, the CR1Dmod
routine handles complex resistivities and offers solutions based
on the full EM-equations as well as the quasi-static approximation.
Thus, modelling of effects based on changes in the magnetic permeability
and the permittivity is also possible.