Installing the 3TB in a borehole
Once you know the deviation of the borehole components, you can instruct the
digitizer to rotate the signals algorithmically.
4.6.1 Installing the Scream! extension
The
Relative Orientation
extension is supplied in the standard Windows distribution
of Scream.
The extension uses Matlab libraries, which are currently only available for Windows.
However, you do not need the full Matlab package to use the extension. The Matlab
runtime libraries are installed as part of the Scream! distribution.
4.6.2 Installing the reference instrument
To measure the orientation of a sensor, you will need a second instrument which is
known to point precisely North. We recommend the use of a Güralp H3, a single-
component horizontal instrument with an elongated "North" pointer. This is
supplied as part of our Borehole Orientation Kit. The instrument should be located
on a solid surface as close to the other instrument as possible. Most boreholes are
constructed with a concrete base around the top of the borehole; If this is present,
we recommend installing the reference sensor there. A good coupling to bedrock is,
however, more important than proximity so, if there is a nearby seismic vault or
basement, you may get better results installing the reference sensor there.
Ideally, the two sensors will be directly connected to the same 6-channel digitizer.
Note:
If you are using separate digitizers, you will need to ensure
they are exactly synchronized. This can be done by connecting GPS
receivers to both digitizers and waiting for the control system of
each one to settle. This process takes at least 12 hours.
Record at least an hour and, ideally, 24 hours of data from both the reference sensor
and the borehole sensor. Try to pick a period when local, cultural noise is at a
minimum: the procedure works best with teleseismic data.
4.6.3 Measuring the orientation
1. Open the recorded files in Scream!. Under Windows, double-click on the .gcf
files in Explorer. Under Linux, you can double-click on the files in Nautilus,
Nemo etc if you have configured your system this way or, from the command
line, you can run
scream --view path_to_.gcf_file…
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Issue G - November 2019
