Installation manual

Echosoundertheory
ifthereisrealshbelowthekeel.Thenumberprovidedtodisplayshabundanceis
relative,andaftersomeuseyourexperiencewillbeavaluablefactorwhenthedecision
ismade.
Thebiomassvalueisalsousedbytheresearchestocalculatehowmuchshthereisin
theocean.Ifyouknowtheshspecieandthesizeofthesh,youcancalculatenumber
ofindividualshesforagivenvolumeofsea.Othermeanstoestablishthenalresult
aretrawlingandcatchdatafromthesherycommunity.
Note
IfyouhaveotherechosoundersorsonarsrunningasynchronouswiththeES70,the
ES70willalsomeasurethetransmitpulsefromthesecondarysystem.Thisiscalled
interference.
YoucanremovetheinterferenceusingthePing-PingFilterfunctionontheActivemenu,but
theES70receiverwillstillpickupthetransmitpulseandimplementitinthecalculations.
Afullsynchronizationofthevariousacousticinstrumentsisrequired.Ifyourownvessel
producesexcessivenoisethiswillalsobetakenintothebiomasscalculationsand
provideyouwithinaccurateinformation.
Relatedtopics
•Biomasslineonpage57
•Biomassinformationpaneonpage59
AboutTVGgain
TVGmeansTimeV ariedGain.WhenTVGisusedin
anechosounder,wealsosometimesrefertoitasdepth
variablegain.
ThepurposeoftheTVGfunctionalityistomakeall
shesappearwiththesameechocolourindependent
oftheirdifferentdepths.
Inmoretechnicalterms,timevariedgain(TVG)isa
signalcompensation.Whentheacousticsignalistransmittedfromtheechosounder
transducer,itissubjectedtolossduetoabsorptionandspreading.First,dependingon
thecurrentsalinityandtemperature,thewaterwillabsorbsomeoftheenergyfromthe
transmission.Theabsorptionlossincreasesastherangeincreases.Second,theenergy
willspreadouttoformacircularbeam.Thewidthofthisbeamalsoincreaseswith
therange.Bothabsorptionandspreadingwillthusreducetheenergy,andbothwill
alsohaveaneffectonthereturnedechosignal.TheTVGcompensationisdesignedto
counteractthesenaturalphenomena,andthisisdoneintheES70usingdigitalsignal
processing.Thedesiredresultisthatshofthesamesizereturnechoesofthesame
strength(colour),regardlessofrange.
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