Using multiple frequencies
A typical Simrad EK60
installation onboard a research vessel will involve several operational
frequencies. Maximum seven can be used, from 18 to 710 kHz.
frequencies are required to cover the broad scope of a marine acoustic
survey. Such surveys range from studies of plankton to large fish
schools from shallow coastal waters down to the deepest oceans.
research has shown that simultaneous use of several discrete echo
sounder frequencies not only improves fish stock estimates, it can
also be used for species identification and discrimination. Each specie
seems to have a unique acoustic frequency response (signature) due
to frequency dependent acoustic backscattering. This new and growing
understanding greatly improves the value of hydroacoustics to obtain
information about marine resources.
software applications may be provided from third party suppliers.
This Simrad EK60 screen capture shows the system operating
with five frequencies simultaneously. The echogram shows a school
of krill, and it is easy to see how this krill shows up differently
for the different operational frequencies. The frequencies used are
18 kHz (top left), 38 kHz (bottom left), 70 kHz (top right), 120 kHz
(middle right) and 200 kHz (bottom right).