In designing Investigator a lot of time was spent looking at the bubble characteristics of the hull using scale models in simulation tanks. Bubbles interfere with the performance of acoustic instruments so to reduce the problem, instruments need to be below the bubble layer created by the hull.
This is achieved by mounting the sensitive acoustic instruments on a large gondola, like a winged keel, mounted 1.2 metres below the hull, well below the bubble zone.
At around 13 metres long and about 9 metres wide, the gondola is able to carry important acoustic instruments including two ‘swath mappers’ to map the seafloor.
Swath mappers use an array of transmitters that send out acoustic signal beam downwards and sideways, and then measure the signal strength and return time on a receiver array. This builds up a topographic map of the sea floor under the ship.
If it is 7 km deep where the seafloor is being mapped, then the total journey of any acoustic signals being sent from the ship and then reflected from the seafloor will be at least 14 km. Given the depths at which mapping will occur any interference can impact on the quality of the signals received and the maps that can be generated. The gondola is important in positioning the swath mappers below the bubble layer and the quietness of the vessel further assists in reducing interference thereby increasing the quality of the maps that can be produced.
The gondola also contains the sub-bottom profiler which can map the sediments of the seabed.
Updated: 27 November 2014