Raymarine e7 - 11.2 The sonar image

11.2Thesonarimage
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.
192e7/e7D—Userreference