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APPENDIX II: Multibeam Survey Suite
Components
8 APPENDIX II: Multibeam Survey Suite Components
8.1 Auxiliary Sensors and Components
A multibeam survey system is comprised of more components than just the Sonic Multibeam
Echosounder. These components are the auxiliary sensors, which are required to provide the
necessary information for a multibeam survey. This does not mean that these sensors are a minor
part of the survey system; each auxiliary sensor is required for any multibeam survey operation.
The required sensor data:
• Position: Differential Global Positioning System Receiver
• Heading: Gyrocompass
• Attitude: Motion Sensor
• Refraction correction: Sound Velocity Probe
Each of the individual sensors requires their setup and operation procedures. The details, discussed
here, concerning the installation and calibration of the auxiliary sensors, is supplemental to any
manufacturer’s documentation.
8.2 Differential Global Positioning System
The Global Positioning System (GPS) is well known to all surveyors. There was a period when the
GPS position was intentionally made less accurate; this was Selective Availability (SA). When SA was
enacted, the GPS position became too inaccurate for survey use. It was during this period that the
concept of differential corrections was established. Differential corrections were derived from users
monitoring the GPS position at a known survey point and computing the corrections required to
adjust the various pseudo ranges to make the GPS position agree with the known survey position. If
a vessel was operating within the local area and observing the same satellite constellation, the
derived pseudo-range corrections could be applied onboard to make for a more accurate and
consistent position. The corrections are normally transmitted over a radio link and applied within
the GPS receiver.
8.2.1 Installation
The first and foremost consideration when installing the DGPS system is the location of the
respective antennae. Both the GPS antenna and the differential antenna (if they are two separate
antennae) need to be mounted on the vessel in such a way to have an unobstructed view of the sky.
When installing the GPS antenna, the surveyor should be aware of the position of the stacks and
masts; in particular, are davits or cranes that may be currently in a stored position, but will be in use
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