Simrad ST90 - Some Means to Reduce Acoustic Noise

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Theillustrationdemonstrateshowtheseabottomandtheseasurfacereturnechoes
backtoyourST90.
AInthissituationyouwillbeabletoidentifytheupperschoolofsh,butthelower
schoolwillbehiddenintheshadowoftheseabedrockformation.
BInthissituationyouwillseeseveralweakechoesfromthewavesandfromtherock
onthebottom,butyouwillstillbeabletoidentifytheschoolofsh.
Thereverberationiscausedbythetransmissionpulseitself.Itcanonlybereducedby
shorteningthepulsedurationorusingasmallerbeamwidth.
Relatedtopics
Acousticnoise,page76
Somemeanstoreduceacousticnoise
Severalfactorsarecontributingtotheperformanceofthehydroacousticequipmentused
onboardavessel.CarefulplanningoftheST90installationmayreducetheacoustic
noise.
Unfortunately,itisimpossibletosimplyprovideanumberofspecicproceduresto
reducethenoise.
Animportantfactoristhephysicallocationofthetransducer.Thisdependsonthe
vessel'sdesignandconstruction,howthehullisshaped,andhowthewaterrunsalong
thehull.Otherfactorsdealwithotherequipmentmountedonboard,andthiswillalsobe
vesseldependant.Atmoderateshipspeedsthemachinerynoiseisusuallydominant.At
mediumspeedstheownoiseincreasesmorerapidlyandtakesover,whileathigher
speedthepropellernoisewillbethemaincontributor.
Note
Theinformationheremustbeconsideredasgeneraladvice.EachST90installation
mustbehandledseparatelydependingonthehulldesignandtheotherelectricaland
mechanicalsystemsinstalledonthevessel.
Reducingownoise
•Theshapeofthetransducer(ordomearoundit)mustbeasstreamlinedaspossible.
SimradST90InstallationManual