Acoustic instruments on the new icebreaker
Some of the most important scientific functions of the ship are the abilities to find and ‘see’ marine organisms such as krill, fish, salps and jellyfish beneath the ship, and to map the seafloor and surrounds.
To do this the ship has many different acoustic instruments, mounted in its hull and two drop keels, which can be lowered up to three metres below the ship. These instruments send pings of sound out into the environment and listen to the returning echo to create images of the surroundings. To work properly, however, they need a relatively quiet environment – a difficult ask in a ship with large engines and propellers.
As a result, a significant amount of work has gone into the design of the ship’s hull and propulsion system, to reduce noise associated with the engines, gear boxes and propellers, as well as bubble formation (which make noise when they pop) and the downward sweep of bubbles which ‘blinds’ the acoustic instruments (see How to build a scientific icebreaker). With this fundamental performance requirement solved, a flexible scientific platform that can react to changing scientific needs has been created.
The new icebreaker's ‘bioacoustic transducers’ can identify when organisms are present and then measure their biomass in the water column. These instruments are mounted in the ship’s hull and drop keels, and listen to the returning echo as pings of sound bounce off objects in the water. If a school of krill, for example, is in the area, the echo will appear as a large, bright mass on associated computer screens. The strength of these returning echoes provide a measure of the amount of biomass in the water column. A team can then drop a net from the back of the ship or through the moon pool, to collect samples from the water.
Other important acoustic instruments are the multi-beam echosounders. A large low frequency multi-beam (8x8 metres in size) will be used to map a swath of the seafloor and continental shelf up to 25 kilometres wide in one pass, and work at depths up to 11 000 metres. A higher frequency multibeam will be used for higher resolution measurements on the continental shelves. A third sideways looking multibeam will allow schools of fish and swarms of krill to be imaged to understand their swirling movements.
Among other things, maps of the seafloor generated using multi-beam echosounders:
- provide insights into the geological and glacial history of the area
- allow scientists to identify areas for further study or for trawls for specific organisms
- provide information about volcanic activity
- provide safer navigational charts in areas close to the Antarctic coast, such as around stations.
Among the other acoustic instruments onboard the new ship are hydrophones to listen for marine mammals, a fisheries sonar that allows scientists to find schools of fish or krill, and Acoustic Doppler Current Profilers, which provide information on the three-dimensional water currents beneath the ship.
For geoscientists, a sub-bottom profiler will generate images of the layers of seafloor sediments and rocks up to 200 metres depth, providing information on the processes of seafloor habitat formation. The sub-bottom profiler will also be used to identify soft sediment suitable for coring. Tiny fossilised plants and animals in these sediment cores, as well as the sediment’s physical and chemical properties, can be analysed for information about past ocean conditions and climate (paleoclimate).