Specifications

University of Pretoria etd – Combrinck, M (2006)
late time values often being more significant) and the fact that the half space (or
background) response often dominates that of the target.
A very simple approach was followed to minimize the effects of these two factors. Data at
every station are presented as a fraction of an average response calculated over the
complete data set. The reasoning behind this is that background (half space or layered
earth) should contribute the most to measured values over a large data set (as conductor
responses are considered “anomalous” to this background). Adding all these responses
together and calculating an average value at each time channel leads to the average
response expected in a specific survey area. The fraction responses (∂B
z
/∂t divided by
average) at every station then show deviations of a station from the average or background
response. The advantage of this type of data presentation above standard profiles is that it
can be displayed as colour contoured pseudo-sections giving the same priority to all time
channels and very successfully enhancing anomalous regions. An example of this
procedure on synthetic data is shown in figure 4.1. The success of this procedure is of
course dependent on a relatively similar background response over a given survey area,
although fairly good results have been obtained in the case history discussed in chapter 5,
which was conducted over a complex geological area. The same presentation of data
(although independently developed) was also found in a paper by Eaton and Hohmann
(1987). In their case, however, the conductor to half space response was considered as a
signal to noise ratio and was examined for different survey geometries.
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