Simrad EK15 - Parameters; TVG Gain

Echosoundertheory
Parameters
Observethefollowingdescriptionsofkeyparameters.
Topics
•TVGgainonpage275
•Outputpoweronpage277
•Pulsedurationonpage279
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,andthisisdoneintheEK15usingdigitalsignal
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.
351718/C
275