Geoscience Reference
In-Depth Information
Air
Ground surface
Layer 1
Object
Layer 2
Layer 3
(a)
e model
Observed field mesurement values
Computed model values
Continuous curve through computed values
Continuous curve through model values
Measurement Location along the Surface
(b) Curve matching computed data and field data
Model
Field measurements
Calculated model values
Te st for match
Match
No match
Result
(c) Flow chart for interpretation using a model
fIGURe 6.16
Generalized process of inversion: (a) computed and field measurement values plotted as a
function of distance along the surface of the ground, (b) the model used to compute the values for the
com-
puted curve
, and (c) a flowchart of the process of inversion.
through the observed field data points. There are some basic rules for deciding on the type of model
to be used for the inversion:
•
The model must be appropriate for the situation at hand. You would not use the numerical
model that represents a sphere to determine the parameters of a pipe.
The model must be relatively easy to compute. It is generally inappropriate to use a model
•
when the forward model takes an enormous amount of computer memory and time to
compute. Several iterations to enable convergence should only take a short period of time
and not require a supercomputer, or should not require a system with massive parallel
processors. Of course, there is the rare situation where it might be appropriate to utilize a
very complicated model.
6.6 SUMMARy
EM methods can be an effective means to locate conductive (metallic) and semiconductive (e.g.,
water and clays) materials in the subsurface. EM methods are rooted in well-known theory and are
