Chapter 2. Introduction
The Güralp Systems borehole orientation sensor provides the hardware required to determine the orientation of a Güralp borehole installation using the Blacknest correlation method.
It is designed for use with borehole installations based on Güralp borehole sensors and DM24 mk3 digitisers, using the additional full-rate data channel of the digitiser to input reference signals with a common time base.
The kit comprises
a low-noise Güralp 3H horizontal instrument with guide rod;
a standard Güralp Systems Hand-held Control Unit for controlling the orientation sensor; and
a cable to attach the surface equipment to your digitiser.
A DM24 or Minimus digitiser with GPS, GPS cable and a power/data cable (for DM24) or power and network cables (for Minimus)
You can also use the kit in other types of installation - e.g. with a down-hole digitiser. To do this, you will need an additional digitiser and a GPS receiver.
Note: The response type of both the Orientation Sensor and the Sensor under examination should be the same. For example, if you are trying to measure the orientation of a down-hole sensor that has acceleration response (V / ms-2) then the orientation sensor must have the same response - i.e. it must also be acceleration (V / ms-2). In the same way, if the sensor that requires orientation has a velocity response, the orientation sensor must also have a velocity response (V / ms-1).
2.1 The Blacknest correlation method
This method was developed at AWE Blacknest in collaboration with Güralp Systems.
A temporary reference sensor is placed at the head of the borehole. This sensor is installed carefully so that its sensitive axis is accurately oriented to North and South.
Ambient ground movements are then recorded by both sensors over a period of time, particularly the natural microseisms which occur constantly with a period in the 1 – 10 second range.
After the experiment, the recorded data from the two horizontal axes of the borehole sensor are rotated algorithmically until they match the corresponding North/South data recorded from the reference instrument.
Güralp Systems' Scream! software is distributed with an extension which uses coherence analysis techniques to perform the relevant calculations automatically.
2.2 About this manual
This manual assumes a degree of familiarity with Güralp Systems' digitisers and Scream! software.
If you need to know more about either of these products, please visit our Web site at
where manuals for all our products are available for download.