Technical information

SimradEK60
Table12Maximumdetectiondepth,splitbeamtransducers
TransducerFrequency
(kHz)
Pulse
duration
(ms)
Bandwidth
(hz)
Txpower
(W)
Rangesh
(m)
Range
bottom(m)
ES18–11188,21382200011007000
ES38B384,0976620009502800
ES70–11702,0515268004501100
ES120–7C1201,0230261000440850
ES200–7C2001,0230881000270550
Theserangecalculationsassumeanormalseawatersalinity(3.5ppt)andtemperature
(+10°C),anaveragebottom(surfacebackscatteringstrength=-20dB)andanoise
leveltypicalforamovingvessel.
Split-beamoperation
TheEK60usesthesplit-beamtechniqueforassessmentofthesizedistributionof
individualsh.Asplit-beamtransduceriselectricallydividedintofourquadrants.All
fourquadrantsareexcitedinparallelduringtransmission.However,thereceivedsignal
fromeachquadrantisseparatelyampliedinafour-channelmatchedreceiverallowing
thedirectionofarrivalofanechotobedetermined.
Figure10Splitbeam
principles
(CD010217K)
A B
Anacousticwavefrontpropagatingtowardsthe
transducerarrivesatthefourquadrantsatdifferent
timescausingthephaseangleoftheelectricaloutput
signalfromthequadrantstodiffer.Thefore-and-aft
angleisdeterminedfromtheelectricalphase
differencebetweentheforeandtheafttransducer
halves,andtheathwartshipsangleisdetermined
fromthestarboardandportsignals.
FishAispositionedalongthetransduceraxiswhere
thetransducerhasitsmaximumsensitivity,while
FishBispositionedtowardstheedgeofthebeam
wherethesensitivityislower.Evidently,theecho
signalfromFishAwillbestrongerthanthesignal
fromFishBeventhoughtheyareofthesamesize
andatthesamedepth.Hence,determiningshsizefromthereceivedechostrength
alonewillnotbetoosuccessful.Asplit-beamechosoundermeasuresthepositionofthe
shwithinthebeam.Thesoundercorrectsforthedifferenceintransducersensitivity
andcomputesthetruesizeofthesh.
Thesplit-beammeasurementtechniqueonlyworksforechoesoriginatingfromone
singleshsincetheelectricalphasewillberandomifechoesfrommultipleindividuals
atdifferentpositionsinthebeamarereceivedsimultaneously.
Consequently,measurementofshsizeinsideaschoolofshtendstobeunreliable.
224
164692/D