Page 446 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

16.6 Types of positioning technologies 439
(a) (b)
(c) (d)
FIGURE 16.11
An LBL system first instructs the responder to interrogate ((a) profile view, (b) plan view) and transponders then reply ((c) profile view, (d) plan view).
system is very accurate and position fixes are very robust compared with the SBL and USBL ver- sions. In addition, the transponder beacons are mounted fixed in the desired reference frame, such as on the seafloor for seafloor surveys or on a ship’s hull for ship hull surveys. This removes most of the problems associated with vessel motion.
The vessel-referenced ship hull positioning system is useful in underwater port security needs (Figures 16.14 and 16.15). This system simply applies the LBL system and uses as a frame of refer- ence the vessel to be surveyed—depicted by scaled drawings of that vessel. In ship hull inspections, certain assumptions can be made allowing positive navigation with only one transponder in “sight.” If only one transponder is communicating, a deduction that the submersible is colocated in the