Kongsberg EM 712, Maintenance Manual, Page: 202 / 232

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About dimensional surveying and alignment
The EM 712 Multibeam echo sounder is a precision instrument for high quality data
collection.
In order to obtain precision data that are both detailed and correct, it is necessary to align
the transducer, measure the location and offset of each sensor in relation to the vessel’s
coordinate system, and calibrate the complete EM 712 prior to use. Modest accuracy
requirements apply when your EM 712 system is only used to investigate objects in
the water column.
The quality assurance tasks required for EM 712 include:
• Aligning the transducer during installation
• Dimensional surveying
• Calibration
The alignment and dimensional surveying must be done during the EM 712 installation
with the vessel in dry dock. The first calibration is normally done at sea during the Sea
Acceptance Test. This calibration may not be complete, and must then be repeated later.
The calibration is then repeated at regular interfaces, and prior to each survey.
Dimensional surveying
Determining the relative positions and orientations of the sensors and the transducer with
high accuracy is important. This can only be met using a survey company/personnel
with good experience in maritime dimensional surveying.
The dimensional surveying tasks required for EM 712 include:
1 Establishing the vessel coordinate system
2 Defining the location of the origin in the coordinate system
3 Establishing waterline with reference to the origin of the coordinate system
4 Setting out the required coordinate reference points throughout the vessel.
5 Defining the vessel’s centre line, and if required — identify this line with physical
markings
6 Measuring the necessary position and angles for all relevant sensors in the
coordinate system.
7 Measuring the location and orientation of the EM 712 transducer in the coordinate
system.
All results from the dimensional survey measurements must be summarized in a report
by the consultants doing the work.
The information provided by the dimensional survey is entered into the EM 712 software
as installation parameters.
Kongsberg EM 712 Maintenance Manual