Installation manual

Echosoundertheory
Alloperationalfrequencieshavedifferentpulsedurations.Thedifferencebetweenfor
examplea50kHzanda38kHztransducerishowevernotlarge:
•A50kHztransducercanbeusedwithpulsedurationsfrom0,12mSto2mS
•A38kHztransducercanbeusedwithpulsedurationsfrom0,26mSto4mS.
Basically,boththesefrequencieswillprovideyouwiththesamedetectionability.A
50kHztransducermayprovidebetterresolutioninshallowwaters,whilethe38kHz
transducermayprovidelongerrangeondeeperwaters.Onthe38kHztransducerthe
shortestpulsedurationis0,26mS.Thisresultsina40cmsoundpulseanda20cm
shseparation.
InordertocontrolthepulsedurationontheSimradES70,usetheNormalOperation
functionontheOperationmenu.
Relatedtopics
•Howtoadjustthepulsedurationonpage98
Aboutbottomslopes
“Bottomslopes”isawellknownphenomenonwithechosounders.Thishappenswhen
thebottomrisessuddenly,andthestartedgeofthetransducerbeamdetectsthebottom
beforetheoppositeedge.
Onemethodforminimizingthe“bottomslopes”phenomenonistouseatransducerwith
narrowbeam,ortoincreasethepulseduration.
AnotherwaytominimizethisphenomenonistoopentheBottomDetectordialog,and
thenchangethesettingforBottomBackstep.Thisfunctioncanalsobeputtootheruse.
Figure40TheBottom
Backstepprinciple
-50dB
-70dB
-30dB
(CD010217-003)
AThepeakofthebottompulse
BDefaultbottombacksteplevel
CApproximatebottombacksteplevelforatsh
detection
DApproximatebottombacksteplevelforseagrass
detection
Thebottompulsebasicallyidentiesthebottomdepth
justpriortothepeakofthepulse(A).However,this
maynotbethetruebottom.Forexample,ifthebottom
pulseisgeneratedbyarockbottomunderathicklayer
ofmud,theactualdepthisslightlyshallower.Forthis
reason,theES70isbydefaultsetuptogiveyouadepthreadingafewmilliseconds
beforethepeakofthepulse.Thisisdonebysettingthebottombackstepleveltoa
defaultvalueof-50dB(B).
Byfurtherdecreasingthelevel(makeitmorenegative)thebottomdetectorwillbecome
more“sensitive”,andthebottomwillbedetectedearlier.
343539/B
115