Kongsberg EM 710, Installation Manual

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alignment
Reference points must be established on the vessel at selected
positions. These are needed during measurements of the sensor
positions. Visual markings at these positions should be prepared
and noted on the vessel drawings with XYZ coordinates in the
vessel coordinate system.
8.3 Sensor location and alignment
• Motion sensor on page 99
• Heading sensor on page 100
• Positioning system on page 100
• Water line on page 100
8.3.1 Motion sensor
The system motion sensor is to provide the multibeam echo
sounder with the angular orientation of the vessel coordinate
system with respect to the gravity vector i.e. roll and pitch
(usually the motion sensor also provides heave and sometimes
heading). The motion sensor must thus know how it is oriented
physically with respect to the vessel coordinate system. The
motion sensor installation manual should be followed with
respect to how this is to be achieved. If the sensor has input
fields for how it is mounted, and the measurement of its
orientation is feasible with an acceptable accuracy and effort, it is
recommended that this done at the same time as the orientation
measurements of the transducers is done. The final accuracy of
the alignment of the sensor should in any case be evaluated and
confirmed by examining the sensor measurement values when
the vessel is in drydock with a known and accurately determined
orientation. A calibration survey should afterwards be performed
at sea to confirm correct performance.
The motion sensor must have a specified accuracy in roll and
pitch of 0.02º or better. Any orientations measurements should
be performed to this accuracy, as must the evaluation of the
measurement data of the sensor. (Note that the most critical
parameter is roll and a pitch accuracy of 0.05º is acceptable.)
The motion sensor must be aligned with the vessel centre line to
an accuracy of 0.1º to avoid that crosscoupling between roll and
pitch measurements degrades the accuracy.
The motion sensor should normally be mounted on the centre
line of the vessel, either close of the multibeam transducers or
close to the vessel’s CG (Centre of Gravity).
The latter point is recommended if the sensor is used for other
purposes than just the multibeam, or if its accuracy is sensitive to
horizontal acceleration.
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