Simrad SU90 - Reducing Noise and Reverberation with the AGC (Automatic Gain Control) Function

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381291/C
ReducingnoiseandreverberationwiththeAGC(Automatic
GainControl)function
Identifyingechoesfromshandschoolscanoftenbechallengingwhentheyare
hiddenbynoiseandreverberation.Whensonarconditionsarepoor,effectivetuningof
theltersintheSU90maybenecessarytoachieveasatisfactoryresult.Automatic
GainControl(AGC)isoneofthetoolsprovidedbytheSU90toremovenoiseand
reverberationfromtheechopresentation.
Context
TheAGC(AutomaticGainControl)functionrunsanautomaticanalysisoftheecho
strength.BasedonthisanalysistheSU90maintainsaproperdynamicrangebasedon
allthecurrentechovalues.Thisisdonebyautomaticallyreducingthegainifyouhave
reverberationandnoise,orincreasingthegainiftheacousticalconditionspermitit.
Tip
ThemostpracticalwaytousetheAGC(AutomaticGainControl)istorstswitchitoff.
Adjusttheechopresentationusingthenormalgainfunctionalityuntilyouhavethe
bestpossibleresult,thenactivatetheAGC.
TheAGCworksbestwithevenbackground(homogenousnoiseconditions)and
pronouncedtargets.Withuniformenvironmentalconditionsyoumaybenetfromstrong
compensation.However ,ifyouarelookingatscatteredsh,reducetheautomaticgain
control,andtrytoaddnormalgaininstead.
Ifyouworkclosetoothervessels,thenoisefromtheirpropellersmaybemisinterpreted
asechoes.Thiswillalsoreducethevisibilityofotherechoes.Thesameappliesifthe
bottomconditionsplaceyourvesselwithdecreasingdepthononesideofthevesseland
yourtargetsontheotherside.Reducetheautomaticgaincontrol.
Ifyouhavealargeschoollocatedclosetoyourvessel(typicallycloserthan150meters)
theschoolgivesyouastrongecho.TheAGCmaymisinterprettheschoolechofornoise.
Reduceordisabletheautomaticgaincontrol.
TheltersintheSU90areimplementedin“series”.Thegaincompensationsaremade
beforetheAGC.Forthisreason,yourcurrentgainsettingwillalwayshaveaneffecton
theautomaticgaincontrol.
Procedure
1Clickinanyviewtomakeitactive.
Theactiveviewisidentiedwithathickerborder.
2OpentheActivemenu.
3SelectAGC(AutomaticGainControl).
SimradSU90OperatorManual