Initial issue
Issue Date 25/06/2010
User Manual: 8142/8182 Transceivers
02 Technical and Functional
Page
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e)
If heading data is present, the processor can compute the position of the vessel (in a
North-referenced grid) relative to a transponder fixed to the seabed.
f)
Without heading data, vessel position would only be known in terms of range, bearing
and elevation from the transponder.
Navigation cycles may contain multiple replies to allow many transponders to be tracked
simultaneously.
3.2
SONARDYNE WIDEBAND®2 SIGNALS
There are more than 600 Sonardyne Wideband®2 signals. The different signals means the system
can be adjusted to various environmental conditions e.g. deep or shallow water and allow accurate
Doppler estimates of the target being tracked.
The latest processing techniques allow range accuracies of millimetres (excluding error contributions’
from environmental effects).
Using the Sonardyne Wideband®2 signals the transceiver will also provide a precise position
estimate. This estimate is then passed to the surface controller as a direction cosine allowing an X, Y,
Z position to be computed by the navigation controller.
3.3
DATA EXCHANGE
The acoustic data exchange between transceiver and transponder is in the form of setting up the
transponder. The acoustic data exchange is also used for data retrieval from the transponder. This
could be a ‘real time’ retrieval of a sensor measurement or an upload of stored data.
The transceiver has many options of acoustic telemetry. It ranges from a secure Spread Spectrum
(SS) wideband telemetry at 100 bps to a High Data Rate (HDR) transmissions of 6000 bps (user
data). The unit has many levels to allow the system to adapt to the most efficient and robust data
exchange.
4
USBL
The USBL system can be used to track Remotely Operated Vehicle (ROV), Tow fish and divers relative to
the vessel. It can also be used as a position sensor for a vessel during Dynamic Positioning (DP).
4.1
ROV/TOW FISH TRACKING
A transponder is placed on an ROV, Tow Fish or diver as applicable. The USBL system will track the
depth and bearing of the ROV, Tow Fish or diver relative to the vessel.
4.2
DYNAMIC POSITIONING
Dynamic Positioning (DP) control of a vessel removes the need to anchor the vessel. The DP system
receives information from the DFE. The DFE receives information from the Vertical Reference Unit
(VRU), Gyro Compass and Digital Global Positioning System (DGPS). A DP vessel is fitted with a
number of thrusters located in the hull, in addition to the main propellers. The thrusters and propellers
are managed by the DP system to keep the vessel on a constant heading and in a constant position
whatever the forces from wind, current and wave action.
For the DP application to function with USBL a reference transponder is placed on the seabed and the
position of the transponder or array in the vessel frame is reported to the DP control system. This is
done by using the repeating acoustic ranging cycles from the transceiver.
Another method is to place a transponder on an ROV following a line feature such as a pipeline. The
USBL/DP system will then control the vessel to follow the ROV. This can be referred to as “The dog
on a lead” or “Follow the Sub” principle.
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