Specifications

University of Pretoria etd – Combrinck, M (2006)
4.5.4 S-layer differential transform compatibility filter
The “returning smoke ring” behaviour illustrated in high conductivity contrast scenarios in
1.3 can also be observed in field data (Figure 4-60).
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0 500 1000 1500 2000 2500 3000 3500 4000
Depth [m]
Cumulative conductance [S]
Figure 4-60: Examples of field data showing "returning smoke ring” behaviour (stations -1200
and -150 from line 4950, Rosh Pinah data set).
Only data conforming to the S-layer differential transform assumption of a monotonously
increasing cumulative conductance curve can successfully be processed with this algorithm.
A filter is therefore designed to only allow data compatible with the transform assumptions
to be processed. This filter discards all data after the first point where a decrease in depth
with an increase in channel number is observed. It also tests for unrealistic increases in
conductance values which sometimes precedes the decreasing depth behaviour.
Specifically, this is implemented as follows.
Step 1: Find the first data point conforming to S-layer late time behaviour.
For each sounding data values are analysed until the first three data points are found which
conform to:
d[i-1]<d[i]<d[i+1] AND
abs((S[i]-S[i-1])/S[i])<1 AND
abs((S[i]-S[i+1])/S[i])<1.
The first data point passed through the filter is
(d[i-1], S[i-1]).
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