Simrad ES80 - Adjusting the TVG (Time Variable Gain) Setting

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AdjustingtheTVG(TimeVariableGain)setting
Whenanacousticpulseissentthroughthewater,itwillgraduallyloseitsenergy.The
greaterthedistancebetweenthetransducerandthetarget(s),thegreaterthelossof
energy.TVG(TimeVariableGain)compensatesforthelossofacousticenergydueto
geometricspreadandabsorption.UsetheTVGbuttonortheEchogramdialogbox.
Context
TheTVG(TimeV aribleGain)compensationisdesignedtocounteractthenatural
phenomenaofgeometricspreadandabsorptionloss.IntheES80,theTVGcompensation
ismadeusingdigitalsignalprocessingsoftware.TheTVGcompensationisexpressed
asalogarithmiccurve.Youcanchoosefromaselectionofcurves.Eachcurvehasa
differentslopecreatingadifferentgaincompensation.Eachcurveisidentiedwiththe
equationXlogTVG.Thecoefcient"X"isaninteger.Typicalvaluesfor"X"are10to40.
Tip
YoucanselectTVGusingthisfunction.YoucanalsoadjusttheTVGsettinginthe
Echogramdialogbox.TheTVGfunctionislocatedontheEchogrampage.
TheES80allowsyoutousedifferentTVGcompensationfortheechoesfromthewater
columnthanfromthebottom.Bymakingthebottomechoesindividuallyadjustable,
youcannetunethepresentationfromthebottomtoinvestigatethebottomtypeand
conditions.TheBottomTVGadjustmenthasnoeffectonshclosetothebottom.To
adjusttheBottomTVG,opentheEchogramdialogbox.
Procedure
1Clickinanyechogramviewtomakeit"active".
Thesettingyouchoosewillonlybevalidforthecurrently"active"echogram.The
"active"echogramviewisidentiedwithathickerborder.
2OpentheActivemenu.
3LocatetheTVGbutton.
4ChooseyourrequestedsettingforTVG(TimeVariableGain).
5SelectApplytoAllifyouwishtousethechosensettingonalltheechogramsof
thesametype.
Relatedtopics
TVGfunction,page414
Echogram:Echogrampage,page424
Aboutsoundwavepropagation,page459
Operatingprocedures