Raymarine c97 - Transducer Bandwidth; The Sonar Image

17.6Transducerbandwidth
Theshnderapplicationdisplaystheshnderfrequency,
centerfrequencyorCHIRPmodedependingontheconnected
sonarmoduleandtransducer.
ExampleofCHIRPsonarmoduleinCHIRPmode.
•WhenusingaCHIRPsonarmodulesettoCHIRPmodeand
awidebandtransducertheCHIRPmodeisshowninthe
shnderapplicationtitlebarandthecenterfrequencyis
displayedon-screen.
•WhenusingaCHIRPsonarmodulesettoanon-CHIRP
modeandawidebandtransducerthecenterfrequencyfor
thetransducerisshownintheshnderapplicationtitlebar
andisdisplayedon-screen.
•WhenusingaCHIRPsonarmoduleconnectedtoa
non-CHIRP(traditional)transducertheCHIRPsonarmodule
willbehavethesameanon-CHIRP(traditional)sonarmodule.
•Whenusinganon-Chirpsonarmodulethetransducer’s
operatingfrequencyisdisplayedintheshnderapplication
titlebarandisdisplayedon-screen.
Note:WhenusingaCHIRPsonarmoduleinnon-CHIRP
modeonlythetransducer’scenterfrequencyisdisplayed,this
maybedifferenttotheactualfrequencytransmitted.
17.7Thesonarimage
Interpretingtheseabedusingsonar
Itisimportanttounderstandhowtocorrectlyinterpretthe
seabedstructurerepresentedintheshnderdisplay.
Theseabedusuallyproducesastrongecho.
Thefollowingimagesshowhowdifferentseabedconditionsare
representedinthesonardisplay:
D6855-3
1
2
3
ItemDescription
1
Ahardbottom(sand)producesa
thinline.
2
Asoftbottom(mudorseaweed
cover)producesawideline.
3Arockyorunevenbottomorawreck
producesanirregularimagewith
peaksandtroughs.
Thedarklayersindicateagoodecho;thelighterareasindicate
weakerechoes.Thiscouldmeanthattheupperlayerissoft
andthereforeallowingsoundwavestopasstothemoresolid
layerbelow.
Itisalsopossiblethatthesoundwavesaremakingtwocomplete
trips–hittingtheseabed,bouncingoffthevessel,thenreecting
offtheseabedagain.Thiscanhappenifthewaterisshallow,
theseabedishard,orthegainissettohigh.
Factorsinuencingthesonardisplay
Thequalityandaccuracyofthedisplaycanbeinuencedbya
numberoffactorsincludingvesselspeed,depth,objectsize,
backgroundnoiseandtransducerfrequency.
Vesselspeed
Theshapeofthetargetchangesalongwithyourspeed.Slower
speedsreturnatter,morehorizontalmarks.Higherspeeds
causethetargettothickenandarchslightly,untilatfastspeeds
themarkresemblesadoubleverticalline.
Targetdepth
Thecloserthetargettothesurface,thelargerthemarkon
screen.
Thedepthofindividualtargetscanbedisplayedbyswitching
ontheTargetDepthIDintheshndermenuMenu>
Presentation.Thenumberoftargetdepthsdisplayedis
inuencedbytheshalarmsensitivitylevel.
Fishnderapplication
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