Simrad TV80 - Page 270

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•Pulseduration
Youcanchoosefrom64µs(CW)128µs(CW),512µs(FM),1024µs(FM)and2048µs
(FM).
ThePulseDurationsettingspeciesthecurrentduration("length")ofthetransmitted
pulse.Theduration("length")ofyourtransmittedpulseisveryimportanttohowyou
candetectsh.
–Ashortpulsedurationgivesyouaveryneverticalresolution.
–Alongpulsedurationthrowsalotmoreenergyintothewater,andthedigitallters
usedbythereceiverarenarrower.
Theshorterpulsesofferahigherresolutionandashorterblankingzone,buttheyare
moreaffectedbynoise.Werecommendusingshortpulselengthonlowtrawls,inthe
tunnelandatthecodend.Thepulselengths512µ,1024µsand2018µsuseFMsweep
(Chirp)technologyandgivehighresolutionevenifthepulselengthislong.However,
thelongestthepulse,thelargesttheblankingzone.Werecommendusing512µs(default
value)andlongerpulsesontrawlsfrom15mandmoreheight.
•TVG
Youcanchoosefrom20dB,30dB,35dBand40dB
Whenanacousticpulseissentthroughthewater,itwillgraduallyloseitsenergy.The
greaterthedistancebetweenthehydrophoneandthetarget(s),thegreaterthelossof
energy.TVG(TimeV ariableGain)compensatesforthelossofacousticenergydueto
geometricspreadandabsorption.
20dBgivesaweakeramplicationfromthebottom.
40dBgivesmoreamplicationfromthebottom,butalsofromsinglesh.
TheTVGcompensationisexpressedasalogarithmiccurve.
•Gain
Youcanchoosefrom1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16
ThepurposeoftheGainfunctionistoadjusttheecholevelintheTV80presentations.
IncombinationwithTVGvalue,selectthebestsettingforyourshingscenario.10isthe
defaultvalue.Gainisalinearfunction.
•Offset
Offsetcanbeusedifyouaremoreinterestedondetailsfrom,forexample,thecentreof
thetrawlanddowntothebottomratherthanthewholetrawlopening.Insteadofhaving
theechogramstartingfromthesensor,youmakeitstartfromadistancefromthesensor.
Thiswillhelpyoufocusonthepartofthetrawlthatismostimportantforyou.
•Learnmode
SimradTV80ReferenceManual