Page 448 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

16.7 Advantages and disadvantages of positioning system types 441
FIGURE 16.14
Depiction of vessel with ship hull inspection system transponders registered onto vessel drawing (M 5 mobile station, AP 5 aft port station, AS 5 aft starboard station, FP 5 forward port station, FS 5 forward starboard station).
quadrant of the ship that contains the requisite transponder can be made as long as the submersible is in visual contact with the hull.
For geo-referenced arrangements, the array of seabed beacons/transponders needs to be calibrated. There are several techniques available for achieving this. The most appropriate tech- nique depends on the requirements of the task and the available hardware. With the continuing integration of LBL, SBL, and USBL systems, intelligent transponder beacons (that measure baselines directly), and satellite navigation systems, the calibration of seabed arrays is becom- ing a quick and simple operation. The operator will be free to choose the techniques appropri- ate to the requirements and the task based upon manufacturer-supplied specifications.
16.7 Advantages and disadvantages of positioning system types USBL advantages:
• Low complexity
• Easy to use
• Good range accuracy
• Ship-based system
USBL disadvantages:
• Detailed calibration of vessel-based transducer assembly required (usually not performed accurately)
• Requires vessel installation of a rigid pole for mounting of the transceiver unit
• Position accuracy depends on ship’s gyro and VRU
• Minimal redundancy
• Large transducer/gate valve requiring accurate/repeatable orientation
SBL advantages:
• Good range accuracy
• Redundancy