Simrad ST90 - Electrical Self Noise; Reverberation

442703/B
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inothervesselsmayalsobealimitingfactor.Theseanoisedependsontheweather
conditions.Inbadweathertheseanoisecanbequitehighduetothewaves.
Relatedtopics
Acousticnoise,page76
Electricalselfnoise
Electricalorelectronicselfnoiseispickeduporgeneratedinanyotherpartofthe
equipmentthanthetransducer.
Humpickedupbythetransducercablesorpickedupfromthepowersupplyisusually
themostcommonsourceofelectricalselfnoise.Athigherfrequencies–whererather
widebandwidthsarenecessary–thenoisefromcomponents,transistorsorother
analogueelectronicmaybealimitingfactor.
Relatedtopics
Acousticnoise,page76
Reverberation
Whenyoutransmitanacousticpulseintothewatertosearchforatarget,echoeswill
alsobereturnedfromanyotherobjectsinthebeam.Theenergyreectedfromthese
"unwanted"objectsisreferredtoasreverberation.
ReverberationisgeneratedwhentheechoesfromyourST90transmissionsarereected
notonlybyshandvalidtargetsinthewater,butalsofromtheseabottomandthe
seasurface.Reverberationisoftenregardedasnoise.Thereareseveraltypesof
reverberation.
•Volumereverberation:Thevolumereverberationiscausedbyminuteplanktonand
air-bubblesinthewater.Thisreverberationhasoftendailycyclesinintensity.
•Surfacereverberation:Thesurfacereverberationdependsontheweathercondition
andthewaves.
•Bottomreverberation:Thebottomreverberationdependsontheroughnessand
physicalpropertiesoftheseabottom.
Reverberationisoftenalimitingfactor,especiallyifyouaresearchingforsmaller
targets.Theechoesfromthebottomwillalwaysdependontheseabottomproperties.
Howuneventheseabediswillaffecttheechoes.Whatkindofbottomyouhaveunder
yourvesselisalsosignicant,asrock,mudorsandwillprovidedifferentreverberation.
Thebottomreverberationusuallymakesitdifculttoinvestigatetargetslocatedclose
totheseabed.
Yourcurrenttiltsettingwillalsohaveaneffectonthereverberation.Theechoesfrom
theseasurfacewillvarywiththecurrentseastateandyourcurrenttiltsetting.
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