Specifications

SimradSH90
Figure6Tilt
(CD015005D)
C
B
A
Thechallengewillalwaysbetondatiltthatpreventstheshechoestobeburiedin
reverberationandbottomechoes.
Ifyouuseahightiltvalue(A)theshwilleasilybedisguisedbythebottomechoes,but
astrongRCGsettingwillhelp.Asthedistancefromthebottomtotheshincreases,
theshwillbeeasiertoseewhentheRCGremovesthebottomechoes.However,this
assumesthattheshechoesareconsiderablystrongerthanthebottomechoes.
Ifyouuseaverysmalltilt(C)youwillnotbebotheredbybottomechoes.Ifthesea
surfaceisgusty,youwillhowevereasilyseeechoesfromthewaves.Theseechoeswill
normallyberatherweak,andwillhardlymoveinrelationtoyourvessel.
Bymeansofamediumtiltangle(B)youwillmostlikelybeabletopickupscattered
shorschoolsifthesearelocatedatsomedistanceabovethebottom.Theupperschool
intheillustrationwillappearonthesonarpicturebeforethebottomecho,whilethe
lowerschoolwilleasilybedisguisedbythebottomechoes.Onceagainyoucanactivate
theRCGfunctiontoimprovethereading.
Noiseandreverberation
Everytimeyouusethesonarthequalityofyoursearchoperationswilldependon
numerouserrorsourcescausedbythenaturalenvironmentandphysicalpropertiesof
yourvessel.Wedistinguishbetweenthetwotermsnoiseandreverberation.
•Noiseisgeneratedbythevessel:engine,propellers,winches,refrigeratingplantsetc.
•Reverberationiscausedbynaturalconditionsinthesea:temperature,salinity,sea
stateandbottomconditions.
Themostcommoncauseofacousticnoiseisthepropellerandthecavitationcausedby
itsrotation.Othertypicalnoisesourcesonboardyourvesselsarewinches,refrigerating
plants,powergenerators,pumpsandcranes.Ifyouexperienceproblemsyouthink
arecausedbynoise,trytondoutwhichsystemthatcausesthenoise,andcontact
yourdealerforadvice.
Topics
•Cavitationonpage107
106
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