Simrad ES80 - About Sound Wave Propagation

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erroneousdepthdetectionsarenevershown.Wheneverthequalityofadetectionis
questionablethealgorithmoutputsadepthof0.00toindicatethatnoreliabledetection
wasobtained.
TheES80algorithmisdesignedtohandleanumberofdifcultsituations.Thealgorithm
maintainsbottomlockforadiscontinuousjumpinbottomdepth.Itavoidsfalsebottom
detectionsonforexampleadenseschoolofsh.Thealgorithmchoosestheupper
boundaryoftherstlayerwhenthebottomconsistsoflayers.
Thebottomdetectionalgorithmlockstotherstgoodbottomreturn.Thedepthatpoint
Aratherthanthedepthalongthetransduceraxiswillbeoutputforaslopedbottom.The
detecteddepthvalueisalwayssmallerthanthedepthalongthetransduceraxisimplying
thatasafetymarginisautomaticallyincluded.
Relatedtopics
ChoosingRangeandStartRangevaluesinasurfacerelatedechogram,page94
ChoosingRangeandStartRangevaluesinabottomrelatedechogram,page95
Rangefunction,page309
StartRangefunction,page310
Aboutsoundwavepropagation
Thevelocityofsoundwavepropagationintheseavariesslightlywithtemperature,
salinityandpressure.
Thevelocityvariesbetween1440and1520m/sinshallowseawater,whileavelocity
around1480m/scanbeexpectedat1000mdepth.Inshallowfreshwaterthevelocityis
approximately1430m/s.Unlessyouhavearelevantsensoravailable,agoodaverage
soundspeedvalueis1470m/s.
TheES80transmitshighenergysoundwavepulsesintothesea.Aatbottomreects
thetransmittedwaveasifitwasamirror.Thepropagatingenergyisspreadoveralarger
andlargerareaasittravelsdowntothebottomandupagain.Theenergyisspreadovera
fourtimeslargerareaeverytimethetraveldistancedoubles.
Conceptdescriptions