Simrad SU90 User Manual

381291/C
73
Relatedtopics
Improvingtherecognitionofshandschoolsusingreceiverlters,page72
ReducingnoiseandreverberationwiththeAGC(AutomaticGainControl)function,
page73
ReducingpropellernoiseandinterferencewiththeNoiseFilter,page74
ReducingbottomandsurfacereverberationwiththeRCG(ReverberationControlled
Gain)function,page75
ReducingnoiseandfalseechoeswiththePing-PingFilter,page77
Adjustingtheintensityoftheechopresentations,page79
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.
Operatingprocedures

Simrad SU90 Specifications

General

Brand	Simrad
Model	SU90
Category	Sonar
Language	English