Simrad ES80 - Page 429

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•Bottom
ABottomechogramismainlyusedwhenyouwishtoexaminetheechoesfrom
shclosetothebottom.Sincethisechogramisreferencedtothebottom,the
seasurfacewillvarywiththeactualdepth,whilethebottomisdrawnat.This
makesiteasytostudytheechoesfromthebottom.Youcaninvestigatethe
bottomconditionsandhardness,anddetectsh.
Theechogramisonlydrawnforpingsthathaveasuccessfulbottomdetection.
•Pelagic
APelagicechogramismainlyusedwhenyouwishtolookatthewatercolumn
startingfromanydistancebelowtheseasurfacedowntowardsthebottom,but
withoutseeingthebottomcontour.Pelagicechogramsareusefulwhenyou
workindeeperwaters.Thereducedrangeandthefactthatyoudonotneedto
waitforthebottomechomeansthattheES80'spingrateisincreased.
InaPelagicechogramthecalculationsdisregardanybottomdetection.All
calculationsarebasedontheentireechogramshownintheview.Ifthebottom
echoispresentintheechogram,thebiomasscalculationwillbewrong.
•Trawl
Trawlsensorsystems(suchasSimradPI,PXandITI)communicateheadrope
depth,and/orthedistancefromtheheadropetothefootrope(trawlopening),
totheES80atregularintervals.Thisinformationisrequiredforthetrawl
echogramtobegenerated.TheTrawlechogramcoverstheverticalopeningof
thetrawlwithreferencetothedepthoftheheadrope.Inadditiontothetrawl
opening,theechogramcoversacertainrangeoverandunderthetrawlopening.
ThebiomasscalculationsinaTrawlechogramarenotrestrictedbythebottom
detection.Thismeansthatthebottomechowillbeincludedinthecalculations
ifitappearswithinthechosenrange.
Theechogramisonlydrawnwhentrawlpositioninformationisavailable.
BottomTVG
UsethisoptiontoselectupaspecicTimeVariableGain(TVG)compensationfor
thebottomdetection.
TheES80allowsyoutousedifferentTVGcompensationfortheechoesfromthe
watercolumnthanfromthebottom.Bymakingthebottomechoesindividually
adjustable,youcannetunethepresentationfromthebottomtoinvestigatethe
bottomtypeandconditions.TheBottomTVGadjustmenthasnoeffectonsh
closetothebottom.
IfyousetBottomTVGtoNonetherewillbenogainchangeintheTVGatthe
detectedbottomdepth.TheTVGselectedfortheechogramisthenusedforthe
entiredepthrange.
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