Raymarine A65 - Transducer Bandwidth; The Sonar Image

15.6Transducerbandwidth
Theshnderapplicationdisplaystheshnderfrequency,center
frequencyorCHIRPmodedependingontheconnectedsonar
moduleandtransducer.
ExampleofCHIRPsonarmoduleinCHIRPmode.
•WhenusingaCHIRPsonarmodulesettoCHIRPmodeanda
widebandtransducertheCHIRPmodeisshownintheshnder
applicationtitlebarandthecenterfrequencyisdisplayed
on-screen.
•WhenusingaCHIRPsonarmodulesettoanon-CHIRPmodeand
awidebandtransducerthecenterfrequencyforthetransducer
isshownintheshnderapplicationtitlebarandisdisplayed
on-screen.
•WhenusingaCHIRPsonarmoduleconnectedtoanon-CHIRP
(traditional)transducertheCHIRPsonarmodulewillbehavethe
sameanon-CHIRP(traditional)sonarmodule.
•Whenusinganon-Chirpsonarmodulethetransducer’soperating
frequencyisdisplayedintheshnderapplicationtitlebarand
isdisplayedon-screen.
Note:WhenusingaCHIRPsonarmoduleinnon-CHIRPmode
onlythetransducer’scenterfrequencyisdisplayed,thismaybe
differenttotheactualfrequencytransmitted.
15.7Thesonarimage
Interpretingtheseabedusingsonar
Itisimportanttounderstandhowtocorrectlyinterprettheseabed
structurerepresentedintheshnderdisplay.
Theseabedusuallyproducesastrongecho.
Thefollowingimagesshowhowdifferentseabedconditionsare
representedinthesonardisplay:
D6855-3
1
2
3
ItemDescription
1
Ahardbottom(sand)producesathin
line.
2
Asoftbottom(mudorseaweedcover)
producesawideline.
3Arockyorunevenbottomorawreck
producesanirregularimagewith
peaksandtroughs.
Thedarklayersindicateagoodecho;thelighterareasindicate
weakerechoes.Thiscouldmeanthattheupperlayerissoftand
thereforeallowingsoundwavestopasstothemoresolidlayer
below.
Itisalsopossiblethatthesoundwavesaremakingtwocomplete
trips–hittingtheseabed,bouncingoffthevessel,thenreecting
offtheseabedagain.Thiscanhappenifthewaterisshallow,the
seabedishard,orthegainissettohigh.
Factorsinuencingthesonardisplay
Thequalityandaccuracyofthedisplaycanbeinuencedbya
numberoffactorsincludingvesselspeed,depth,objectsize,
backgroundnoiseandtransducerfrequency.
Vesselspeed
Theshapeofthetargetchangesalongwithyourspeed.Slower
speedsreturnatter,morehorizontalmarks.Higherspeedscause
thetargettothickenandarchslightly,untilatfastspeedsthemark
resemblesadoubleverticalline.
Targetdepth
Thecloserthetargettothesurface,thelargerthemarkonscreen.
Thedepthofindividualtargetscanbedisplayedbyswitchingonthe
TargetDepthIDintheshndermenuMenu>Presentation.The
numberoftargetdepthsdisplayedisinuencedbytheshalarm
sensitivitylevel.
Usingtheshnder
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