Raymarine C140w - Page 103

MultipleEchoes
Multipleechoesarenotverycommonbutcanoccurifthereisalarge
targetwithawideverticalsurfaceatacomparativelyshortrange.
Thetransmittedsignalwillbereectedbackandforthbetweenthe
targetandyourownship,resultinginmultipleechoes,displayed
beyondtherangeofthetruetargetecho,butonthesamebearing.
D1642-3
True echo
Multiple echoes
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.
D3968-4
RainorSnowClutter
Theradarcanseeechoesfromrainorsnow.Returnsfromstorm
areasandrainsquallsconsistofcountlesssmallechoesthat
continuouslychangesize,intensityandposition.Thesereturns
sometimesappearaslargehazyareas,dependingontheintensity
oftherainfallorsnowinthestormcell.
D3967-4
Usingradar
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