Installation manual

Echosoundertheory
Bottomecho
Ahardatbottomreectsthetransmittedsignalasifitwasamirror.Thetransmitted
pulsehitstheilluminatedbottomareaatnearlythesameinstant,andtheechofrom
differentpartsofthisareaarrivebackatthesurfacealsoatnearlythesameinstant.
Figure4Bottomecho
principles
(CD010217I)
A
B
Thereceivedechosignalisbasicallyanattenuated
copyoftheshorttransmitpulse.Theechosignal
fromaslopedbottomischaracterizedbyhavinga
longerdurationandaslowerriseandfalltime.The
transmittedpulsersthitstheslopeatpoint(A),
andastimeelapsesthereectionpointtravelsalong
theslopetowardspoint(B).Manylocationsdonot
haveasolidhardbottom.Frequently,thebottom
iscomposedoflayersofmud,clayandsandwhich
canbeobservedascolouredbandsontheecho
sounderdisplay.
Thebottomdetectionalgorithmisimplemented
solelyinsoftware,andseparatealgorithmsare
runforeachfrequencychannel.Thealgorithmis
designedwithemphasisonreliabilityinthesensethaterroneousdepthdetectionsare
neveroutput.Wheneverthequalityofadetectionisquestionablethealgorithmoutputsa
depthof0.00toindicatethatnoreliabledetectionwasobtained.TheES70algorithm
isdesignedtohandleanumberofdifcultsituations.Thealgorithmmaintainsbottom
lockforadiscontinuousjumpinbottomdepth.Itavoidsfalsebottomdetectionsona
denseschoolofsh.Thealgorithmchoosestheupperboundaryoftherstlayerwhen
thebottomconsistsoflayers.
Thebottomdetectionalgorithmlockstotherstgoodbottomreturn.Thedepthatpoint
Aratherthanthedepthalongthetransduceraxiswillbeoutputforaslopedbottom.The
detecteddepthvalueisalwayssmallerthanthedepthalongthetransduceraxisimplying
thatasafetymarginisautomaticallyincluded.
Wavepropagation
Thevelocityofsoundwavepropagationintheseavariesslightlywithtemperature,
salinityandpressure.Thevelocityvariesbetween1440and1520m/sinshallowsea
water,whileavelocityaround1480m/scanbeexpectedat1000mdepth.Inshallow
freshwaterthevelocityisapproximately1430m/s.
AgoodaveragevaluetobeusedintheEnvironmentdialogis1470m/s.
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