Simrad ES80 - Adjusting the TVG in the Echogram Dialog Box

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AdjustingtheTVGintheEchogramdialogbox
TheTimeV ariedGain(TVG)canbedenedintheEchogramdialogbox,orbymeans
oftheTVGfunctionontheActivemenu.
Context
Whenanacousticpulseissentthroughthewater,itwillgraduallyloseitsenergy.
Thegreaterthedistancebetweenthetransducerandthetarget(s),thegreatertheloss
ofenergy.
•Geometricspread:Oncetransmitted,theacousticenergywillspreadouttoforma
circularbeam.Thewidthofthisbeamincreaseswiththephysicaldistancetothe
target(s).
•Absorptionloss:Dependingonthesalinityandtemperature,thewaterwillabsorb
someoftheenergyfromthetransmission.Theabsorptionlossincreasesasthe
physicaldistancetothetarget(s)increases.
Boththegeometricspreadandtheabsorptionwillalsohaveaneffectonthereturnedecho
signal.Thatiswhywenormallyrefertothesefactorsasthetwo-waytransmissionloss.
TheTVG(TimeV aribleGain)compensationisdesignedtocounteractthenatural
phenomenaofgeometricspreadandabsorptionloss.IntheES80,theTVGcompensation
ismadeusingdigitalsignalprocessingsoftware.
TheTVGcompensationisexpressedasalogarithmiccurve.Youcanchoosefrom
aselectionofcurves.Eachcurvehasadifferentslopecreatingadifferentgain
compensation.EachcurveisidentiedwiththeequationXlogTVG.Thecoefcient"X"
isaninteger.Typicalvaluesfor"X"are10to40.
SeveralTVGcompensationsettingsareavailable.
•NoTVG
TVGcompensationisnotimplemented.Thissettingishardlyeverused.
•School(20logR)
Thisgainsettingoffersweakeramplicationclosetothebottom.Ithasbeendesigned
toprovidethebestechoesforschools.Thephysicalsizeofaschoolallowsyouto
detectitevenwithreducedgain.
•Fish(40logR)
Thisgainsettingprovideslargeramplicationclosertothebottom.Ithasbeen
designedtoprovidethebestechoesfromsinglesh.
•Targets(40logR)
ThissettingusesthesameTVGamplicationasFish(40logR),butadditionalltering
andcompensationisimplemented.
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