Echo sounders are used to find fish in the ocean, observe their behaviour, and estimate their quantity and size as well as the abundance and distribution of the plankton upon which fish feed.
Research vessels and many fishing vessels typically use echo sounders that send and receive signals on up to six frequencies. Norwegian researchers have now developed an echo sounder that works on 100 frequencies simultaneously.
Quantum leap in fisheries acoustics
Currently, multiple echo sounders working in parallel on different frequencies are needed in order to identify marine organisms below the surface. A specific target -- a school of mackerel, for instance -- can be singled out by analysing all the elements within the echo sounder image (called an echogram) and removing the echoes from other species such as herring, cod and plankton. This creates an echogram showing only the seabed and the mackerel.
"Our new wideband echo sounder sends signals on all its frequencies at once, which is equivalent to 100 echo sounders operating on one frequency each," explains Principal Scientist Egil Ona of the Institute of Marine Research in Bergen. "This makes it so much better at identifying fish and zooplankton, we consider it a quantum leap in fisheries acoustics."
Dr Ona heads the project "Exploiting new wideband echo sounder technology for zooplankton characterization, sizing and abundance estimation (WESTZOO)," which has received funding from the Research Council of Norway's research programme on the Oceans and Coastal Areas (HAVKYST).
Much higher resolution
Initially, the project researchers focused on zooplankton, since the echo from these marine organisms was so well suited to the available frequency band. Later, they tried out the wideband echo sounder on fish and other targets.
"The experimental results are extremely promising," says Dr Ona. "The new system provides much better information about the target. In addition, the echograms are of far higher resolution, enabling us to identify various species more accurately than before."
"The potential of this new echo sounder far exceeds current systems, " says Dr Ona. The new product will hit the market in 2013, commercialised by the technology company Simrad, a part of Kongsberg Maritime AS. Simrad is a partner in the WESTZOO project.
Images from the deep
The WESTZOO project has yielded exciting results in addition to the new echo sounder technology. For instance, the researchers have developed a stereo camera method for photographing the organisms being measured in ocean depths. The photos are used to verify the patterns and other data detected by the echo sounder.
The researchers have also constructed an acoustic probe that can quantify and distinguish fish and plankton down to depths of 1 500 metres. "We are confident," says Egil Ona, "that this will become a standard tool on a lot of research vessels in the future."
Materials provided by The Research Council of Norway. Original written by Sven Øvergaard/Elisabeth Skjønsberg; translation by Darren McKellep/Carol B. Eckmann. Note: Content may be edited for style and length.
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