Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

Only in this special case will be jus.tificati.on .to neglect the
term oEa at low fr2quenaies and to use the approximation
.to calculate the internal conducti.vj.ty anomaly o from the ano-
a
malous current density and the normal electric field, St w i l l
be advisable to regard here rsa as a sole functi.on of x and y
and thus to postulate the same depth dependence for the anomalous
current and the normal electric field.
Interpretation with numerical models
So far idealized models for a laterally non-uniform subs-tructure
have been considered. They allowed a simplified treatment of
the induction problem and had in common that only few free para-
meters were involved. Once numerical values were attached to
them, the observed surface anomaly of the variation field could
,be converted rather easily into variable model parameters to
characterize the internal change of subsurface conductivity at
some given depth from site to site.
The introduction of more realistic models le'ads to a substantial
increase of the numerical work involved and should be considered
only, if transfer functions for the anomalous surface field are
known with high accuracy. The inverse problem to derive a set
of variable model parameters directly from observations can be
solved by linearisation, i.e. by the introduction of a linear
data kernel, connecting changes of the surface response to
changes in the subsurface conductivity structure (cf. Sec.6).
As before a normal structure o outside of the anomaly is given,
n
the variable model parameters representing only lateral changes
of o with respect to on within the range of the anomaly. Unless