Installing the 3TB in a borehole
The lower graph shows the overall amplitude similarity of the rotated signal.
This provides an idea of the sign of the coherence (since signals in perfect
antiphase have a high coherence as well as those in phase). If there are two
peaks in the coherence graph, the correct one is where the amplitude
similarity is most positive.
The sample plots show that the borehole instrument is installed with its N/S
axis at a bearing of –90° from true North.
7. The second window shows the result of applying the rotation to the signal,
i.e.
the time series that a sensor in perfect N/S orientation would have produced:
8. You can perform more accurate calculations by narrowing the search range.
This is done in the two left-hand-side entry boxes on the Coherence vs Angle
window: the first denotes the centre of the new search and the second
specifies its range. The program suggests suitable values for you, so in most
cases you can just click
to perform another iteration.
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Issue G - November 2019
