Garmin G1000H Marine Radio User Manual


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Garmin G1000H
™
Pilot’s Guide for the Bell 407GX
190-01255-00 Rev. B328
HAZARD AVOIDANCE
No Radar Coverage
Figure 6-57 Precipitation Data Legend
Boundary of GFDS
weather data request
ThedisplayofradarcoverageisenabledwhenPrecipitationisselectedfordisplay.Areaswhereprecipitation
radarcoverageisnotcurrentlyavailableorisnotbeingcollectedareindicatedingrayshadeofpurple.A
white boundaryline with whitetick marks depictsthe selected coveragearea ofthe GFDSweather data
request.Thisboundaryenclosestheprecipitationdatawhenthisweatherproductisdisplayed.
ReFlectivity
Reectivityistheamountoftransmittedpowerreturnedtotheradarreceiver.ColorsonthePrecipitation
displaydirectlycorrelatetothelevelofdetectedreectivity.Reectivityasitrelatestohazardousweather
canbeverycomplex.
Theroleofradarisessentiallytodetectmoistureintheatmosphere.Simplyput,certaintypesofweather
reectradarbetterthanothers.Theintensityofaradarreectionisnotnecessarilyanindicationofthe
weatherhazardlevel.Forinstance,wethailreturnsastrongradarreection,whiledryhaildoesnot.Both
wetanddryhailcanbeextremelyhazardous.
Thedifferentradarechointensitiesaremeasuredindecibels(dB)relativetoreectivity(Z).Weather
radars measure the reflectivity ratio, or the energy reflected
backto
theradarreceiver(
designatedbythe
letterZ)
.ThevalueofZincreasesasthereturnedsignalstrengthincreases.
PReciPitatiOn limitatiOns
Radarimagesmayhavecertainlimitations:
•Radar composite reectivity does not provide sufcient information to determine cloud layers or
precipitationcharacteristics(wethailvs.rain).Forexample,itisnotpossibletodistinguishbetweenwet
snow, wet hail, and rain.
•Anindividualradarsitecannotdepicthighaltitudestormsatcloseranges.Ithasnoinformationabout
storms directly over the site.
•Whenzoomedintoarangeof30nm,eachsquareblockonthedisplayrepresentsanareaoffoursquare
kilometers.
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