iXBlue GAPS, User Manual

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GAPS
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User Guide
3.2 Installing the Acoustic Antenna
3.2.1 R
ECOMMENDATIONS
Containing its own attitude sensor, GAPS can be installed at the location and in the position
that best suit the operational constraints. Nevertheless, some factors concerning the
installation can decrease the final global system performances if not taken into account.
3.2.1.1 Cable Curvature
As seen in section 2.2.3, the integration of the GAPS head must allow a space around the
main connector. This space corresponds to the minimum bending radius (75 mm) of the main
cable and the minimum rigid length (150 mm) of the SUBCONN connector.
3.2.1.2 Environmental Noise
As every acoustic system, the noise generated by the environment lower the system
performance. Positioning range and accuracy depend on the signal to noise ratio.
On a ship, it is recommended to install the GAPS head in the front third of the ship (in order to
decrease the noise level from the propeller) and as far as possible from any water discharge
system.
3.2.1.3 Reflective Surfaces
Even though the MFSK signal processing increases the multi- path immunity, there are
situations where the direct signal detection is disturbed by reflective signals. To avoid such
cases, we recommend keeping GAPS at least 1 m away from reflective surfaces.
The sea surface may be considered as a reflective surface depending on the depth of the
transponder: if both the transponder and the acoustic array are close to the surface, there will
be multi-path phenomenon at specific distances.
The transponder depth is usually an operational constraint and therefore difficult to change. In
that case, it is recommended to increase the depth of GAPS. For deep-water applications
(more than 250 m), a depth of 1 m is usually enough for the acoustic array.
MU-GAPS-AN-005-H - November 2019 37