| dc.description.abstract | There is a current desire to harvest marine resources by managing total marine
ecosystems rather than single species of the ecosystems. By means of algorithms
applied on high-quality multi-frequency acoustic data, species, or rather acoustic
categories, of the ecosystem can be identified. This information may significantly
increase the accuracy of acoustic survey estimates of fish and to some extent also
for zooplankton. Multi-frequency split beam echo sounders with nearly identical
and overlapping acoustic beams have been regularly used in acoustic surveys for
fish stock abundance estimation at Institute of Marine Research for the last five
years. Calibrated raw data from up to six simultaneously working echo sounders at
18, 38, 70, 120, 200 and 364 kHz was used as input to a stepwise, modular sequence
of analysis, like bottom detection, noise quantification and removal, target
categorisation and school detection in near real-time. Direct generation of new,
synthetic echograms, based upon the measured or modelled relative frequency
response of the targets is one of the most useful features of the systems. The result
of the categorisation process can be used to show the spatial distribution of different
acoustic categories in a single synthetic echogram, or to keep some and remove
other acoustic categories in echograms at a single frequency. | no_NO |
