Simrad ST90 - Page 68

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Thechallengeistondatiltthatpreventstheshechoestobe"buried"inreverberation
andbottomechoes.
•Ifyouuseahightiltvalue(A)theshareeasilydisguisedbybottomechoes.Astrong
RCG(ReverberationControlledGain)settingwillremovethebottomechoes.Asthe
distancefromthebottomtotheshincreases,theshechoesbecomeclearer.However,
thisassumesthattheshechoesareconsiderablystrongerthanthebottomechoes.
•Ifyouuseaverysmalltilt(C)youarenotbotheredbybottomechoes.However,ifthe
seasurfaceisgustyyouwillseeechoesfromthewaves.Theseechoesarenormally
ratherweak,andtheyhardlymoveinrelationtoyourvessel.
•Bymeansofamediumtiltangle(B)youareabletopickupscatteredshorschoolsif
thesearelocatedatsomedistanceabovethebottom.Theupperschoolintheillustration
appearsonthesonarpicturebeforethebottomecho,whilethelowerschoolwilleasily
bedisguisedbythebottomechoes.OnceagainyoucanactivatetheRCGfunctionto
improvethereading.
Tip
WiththevariousbeamsprovidedbytheST90,itmaybedifculttounderstandtheconcept.
Howdothesebeams"behave"inthewater?Bymeansofagraphicpresentation,theBeam
Visualizationdialogboxattemptstogiveyouabetterunderstandingofhowtheacoustic
beamsaretransmittedintothewater .OpentheBeamVisualizationdialogboxfromthe
Setupmenu.
Procedure
1Clickinanyviewtomakeitactive.
Theactiveviewisidentiedwithathickerborder.UnlessyouusetheApplytoall
function,allchangesyoumakewillonlybeappliedtothisview.
2InaVerticalview,clickonthetiltline,keepthemousebuttondepressed,anddrag
thelineupordown.
Optionally:
SimradST90OperatorManual