Installation manual

Echosoundertheory
Parameters
Observethefollowingdescriptionsofkeyparameters.
Topics
•TVGgainonpage123
•Outputpoweronpage125
•Pulsedurationonpage127
•Rangeselectiononpage129
TVGgain
TVGmeansTimeV ariedGain.WhenTVGisusedin
anechosounder,wealsosometimesrefertoitasdepth
variablegain.
ThepurposeoftheTVGfunctionalityistomakeall
shesappearwiththesameechocolourindependent
oftheirdifferentdepths.
Inmoretechnicalterms,timevariedgain(TVG)isa
signalcompensation.Whentheacousticsignalistransmittedfromtheechosounder
transducer,itissubjectedtolossduetoabsorptionandspreading.First,dependingon
thecurrentsalinityandtemperature,thewaterwillabsorbsomeoftheenergyfromthe
transmission.Theabsorptionlossincreasesastherangeincreases.Second,theenergy
willspreadouttoformacircularbeam.Thewidthofthisbeamalsoincreaseswith
therange.Bothabsorptionandspreadingwillthusreducetheenergy,andbothwill
alsohaveaneffectonthereturnedechosignal.TheTVGcompensationisdesignedto
counteractthesenaturalphenomena,andthisisdoneintheES70usingdigitalsignal
processing.Thedesiredresultisthatshofthesamesizereturnechoesofthesame
strength(colour),regardlessofrange.
ThefollowingTVGsettingsareavailable:
aPower(NoTVG)
TVGgainisnotimplemented.Thissettingishardlyeverused.
bSchool(20logTVG)
Thisgainsettingoffersweakeramplicationclosetothebottom.Ithasbeen
designedtoprovidethebestechoesforschools.Thephysicalsizeofaschoolallows
youtodetectitevenwithreducedgain.
cFish(40logTVG)
Thisgainsettingprovideslargeramplicationclosetothebottom.Ithasbeen
designedtoprovidethebestechoesfromsinglesh.
343539/C
123