GAPS - User Guide
2 Conventions and Specifications
2.1 Conventions
2.1.1 CENTER OF MEASUREMENTS, ACOUSTIC CENTER AND REFERENCE AXES
Center of
measurements
The GAPS center of measurements is in the center of the mounting flange of the acoustic
antenna. In the Web-User Interface, the GAPS center of measurement is equivalent to the
CRP (Common Reference point). The GAPS center of measurement is the reference point for
the determination of external sensor (i.e., GPS) lever arms.
GAPS Acoustic
Center
The distance between the center of the measurements (center of the top flange) and the
acoustic center is approximately 0.6 m (589.3 mm). The acoustic center is at the barycenter of
the four hydrophones.
Reference
frames
The lever arms of the external sensor with respect to the GAPS center of measurements is
represented by three lengths LV1, LV2, LV3 defining the position of the external sensor in the
(XV1, XV2, XV3) vessel reference axes.
Figure 8 - Center of measurement and reference axes
Misalignment
The misalignments of the acoustic antenna are measured between the reference frame of
GAPS and the reference frame of the vessel. The three misalignment angles are entered by
the operator in the Web-User Interface (MECHANICAL PARAMETERS menu).
2.1.2 HYDROPHONES AND REFERENCE FRAME
GAPS reference frame is based on H1, H2, H3 and H4 hydrophones. H1 must be directed
towards the bow of the ship. Hydrophone names are printed above the arms.
Figure 9 - H1 and H2 hydrophones
MU-GAPS-AN-005-H - November 2019 23
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