Raymarine e7 - Page 139

IndirectEchoes
Thereareseveraltypesofindirectechoesorghostimages.These
sometimeshavetheappearanceoftrueechoes,butingeneralthey
areintermittentandpoorlydened.
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3
2
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5
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ItemDescription
1Falseecho
2Trueecho
3Passingship
4
Mastorfunnel
5
Trueecho
6Falseecho
MultipleEchoes
Multipleechoesarenotverycommonbutcanoccurifthereisalarge
targetwithawideverticalsurfaceatacomparativelyshortrange.
Thetransmittedsignalwillbereectedbackandforthbetweenthe
targetandyourownship,resultinginmultipleechoes,displayed
beyondtherangeofthetruetargetecho,butonthesamebearing.
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ItemDescription
1Trueecho
2Multipleechoes
BlindSectors
Obstructionssuchasfunnelsandmastsneartheradarantenna
mayobstructtheradarbeamandcauseradarshadowsor‘blind
sectors’.Iftheobstructionisrelativelynarrow,therewillbea
reductionofthebeamintensity,thoughnotnecessarilyacomplete
cut-off.However,forwiderobstructionstheremaybeatotallossof
signalintheshadowarea.Theremayalsobemultipleechoeswhich
extendbehindtheobstruction.Blindsectoreffectscannormallybe
minimizedbycarefulselectionofthescannersitepriortoinstallation.
SeaClutter
Radarreturnsfromwavesaroundthevesselcanclutterthecentre
oftheradarpicture,makingitdifculttodetectrealtargets.Such
‘seaclutter’usuallyappearsasmultipleechoesonthedisplayat
shortrangescales,andtheechoesarenotrepetitiveorconsistent
inposition.Withhighwindsandextremeconditions,echoesfrom
seacluttermaycausedensebackgroundclutterintheshapeof
analmostsoliddisc.
Usingradar
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