Simrad TV80 - Page 234

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PulseDuration
ThePulseDurationsettingspeciesthecurrentduration("length")ofthetransmitted
pulse.Theduration("length")ofyourtransmittedpulseisveryimportanttohow
youcandetectsh.
•Ashortpulsedurationgivesyouaveryneverticalresolution.
•Alongpulsedurationthrowsalotmoreenergyintothewater,andthedigitallters
usedbythereceiverarenarrower.
TVG
ThepurposeoftheTVGcompensationistomaketargetsofthesamesizeproduce
echoesofthesamesize,regardlessoftherange.TimeV ariableGain(TVG)isapplied
totheechosignalsbeforetheyaredisplayed.TheTV80canworkwithseveral
differentTVGcompensationsettings.Thedefaultvalueisshownwithanasterisk.
Whenanacousticpulseissentthroughthewater,itwillgraduallyloseitsenergy.The
greaterthedistancebetweenthehydrophoneandthetarget(s),thegreaterthelossof
energy.Signalsreceivedfromlongrangesareampliedtocompensateforlosses
duetogeometricspreadandabsorption.Bymeansofalgorithms,thetimevariable
gaincompensationconvertstheechopresentationasafunctionofrange.Thismakes
thetargetswiththesamestrengthappearwiththesameintensityindependentof
theirphysicaldistancefromthehydrophone.TheTVGcompensationisexpressed
asalogarithmiccurve.
Gain
ThepurposeoftheGainfunctionistoadjusttheecholevelintheTV80presentations.
Itcontrolshowmuchamplicationthatisappliedtothereceivedechoes.Thedefault
valueisshownwithanasterisk.
Offset
Offsetcanbeusedifyouaremoreinterestedondetailsfrom,forexample,thecentre
ofthetrawlanddowntothebottomratherthanthewholetrawlopening.Insteadof
havingtheechogramstartingfromthesensor,youmakeitstartfromadistancefrom
thesensor.Thiswillhelpyoufocusonthepartofthetrawlthatismostimportantfor
you.Thedefaultvalueisshownwithanasterisk.
SimradTV80ReferenceManual