Simrad SU90 - Electrical Noise; Reverberation; Some Means to Reduce the Noise

SimradSU90
Electricalnoise
Electricalorelectronicnoiseispickeduporgeneratedinanyotherpartoftheequipment
thanthetransducer.Humpickedupbythetransducercablesorpickedupfromthe
voltagesupplyisusuallythemostcommonsourceofelectricalnoise.Athigher
frequencieswhereratherwidebandwidthsarenecessarythenoisefromcomponents,
transistorsorotheranalogueelectronicmaybealimitingfactor.
Reverberation
Theenergyreectedfromotherobjectsthantheonewewantedtoobserveiscalled
reverberation.Wehavetwokindsofreverberation:
1Volumereverberation
Thevolumereverberationiscausedbyminuteplanktonandair-bubblesinthewater.
Thisreverberationoftenhasdailycyclesinintensity.
2Surfaceandbottomreverberation
Thesurfacereverberationisdependentontheweathercondition,whilethebottom
reverberationdependsontheroughnessofthebottom.
Thereverberationisoftenalimitingfactorforthesonar,especiallyifyouaresearching
forsmallertargets.Thereverberationiscausedbythetransmissionpulseitselfand
canonlybereducedbyshorteningthepulsedurationorusinganarrowerbeamwidth.
Thebottomreverberationusuallymakeitdifculttoinvestigatetargetslocatedclose
totheseabed.
Somemeanstoreducethenoise
Carefulplanningofthehullunitinstallationmayreducethenoise.
Unfortunately,itisimpossibletosimplyprovideanumberofspecicproceduresto
reducethenoise.Animportantfactoristhephysicallocationofthetransducer,andthis
dependsonthevessel'sdesignandconstruction,howthehullisshaped,andhowthe
waterrunsalongthehull.Otherfactorsdealwithotherequipmentmountedonboard,
andthiswillalsobevesseldependant.
Atmoderateshipspeedsthemachinerynoiseisusuallydominant.Atmediumspeedsthe
ownoiseincreasesmorerapidlyandtakesover,whileathigherspeedthepropeller
noisewillbethemaincontributor.
Note
Theinformationheremustbeconsideredasgeneraladvice.EachSU90installation
mustbehandledseparatelydependingonthehulldesignandtheotherelectricaland
mechanicalsystemsinstalled.
Reducingownoise
1Theshapeofthetransducerordomeshouldbeasstreamlinedaspossible.The
fairingaroundtheinstallationtrunkshouldalsobestreamlined.
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