Installation manual

SimradES70
Ontheechogramthewhitelinewillthen“climb”uptheslope.Makesurethatyoudo
notincreasethesensitivitytoomuch.Thiswillhaveaneffectontheshdetection
onaatbottom,andthebiomassvalueswillbewrong.Ourexperienceshowthatan
approximately-75dBbottombackstepvaluecanbeusedsafely.
Byincreasingthebottombackstepvalue(makeitmorepositive)thebottomwillbe
detectedlater,anditwillappeartobedeeper.
Tip
Ruleofthumb:
•Reducethebottombacksteplevel(makeitmorenegative)todetectthebottomearlier,
andthusincreasebottomdetection“sensitivity”.
•Increasethebottombacksteplevel(makeitmorepositive)todetectthebottomlater,
andthusincrease“penetration”.
Figure41Bottomslopes
(CD010217-002)
Example13Bottomslopes
Theedgeofthebeam(A)
hitsthebottomrst,andstarts
togiveanecho.Thebottom
detectorintheES70measures
thestrongestecho,detectswhat
itthinksisthebottom,and
startsthewhiteline.
Theareaabovethebottom
detection(B)willbemasked
off,andeventhoughitmay
containshthesewillnot
bevisiblebecausetheecho
fromthebottomisstronger
thanthosefromthesh.The
estimateddepth(C)willbe
shown.
OntheES70thephenomenon
willcausethebottomline(E)tobedistorted.
Example14UsingtheBottomBackstepparameterforseagrassdetection
IfyouuseanOlexsystem,youcantakeadvantageoftheBottomBackstep
parametertodetectseagrass.Decreasethebottombackstepvalue(makeit
morenegative)sothatthebottomisdetectedatthetopofanareaofseagrass.
TheOlexwillthendetecttherealbottom,andtheresultistheheightof
theseagrass.
→Howtoadjustthebottomdetectiontondseagrassonpage92
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