Specifications

University of Pretoria etd – Combrinck, M (2006)
σ
Plate
= 0.2 S/m
l
Plate
= 100 m, 200 m,
300 m, 400 m
d
Plate
= 150 m
conductivities below
prism.
Conductive prism
in half space
(varying hor.
dimensions)
σ
HS
= 0.02 S/m
σ
Plate
= 2 S/m
l
Plate
= 100 m, 200 m,
300 m, 400 m
d
Plate
= 150 m
100m still not resolved.
Decreasing depth with
increasing time for
300m and 400m prisms.
Behaviour similar to infinite
high contrast plates with
overestimation of depths
and negative conductivities
below prisms.
High contrast.
In general the S-layer differential transform performs more reliably in low contrast
environments although the “decreasing depth with increasing time” behaviour serves as a
very important indicator of high contrast conductors. Keeping in mind that depths will be
overestimated in this event (and underestimated for conductors with dimensions less than
300m) still allows the results to be interpreted accurately for the presence of a conductor
even if there are constraints on the accuracy of depth to top in some cases. The depth to
bottom cannot be determined from this algorithm. Imaged conductivities approach true
conductivities for very thick layers (half space and two layer case) but this is not the case
for confined conductors. However, the imaged conductivity behaviour can be used
successfully to indicate “lower”, “higher” and “much higher” conductivities. Negative
conductivities should not be just be discarded as invalid as it can be indicative of small
confined conductors at shallower depths as well as the presence of high contrast
conductors. In fact, the exact cause of negative conductivities for every instance can be
found by inspection of the cumulative conductance curves if needed.
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