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Garmin G1000 Pilot’s Guide for Cessna Nav III
190-00498-07 Rev. A
SYSTEM
OVERVIEW
FLIGHT
INSTRUMENTS
EIS
AUDIO PANEL
& CNS
FLIGHT
MANAGEMENT
HAZARD
AVOIDANCE
AFCS
ADDITIONAL
FEATURES
APPENDICESINDEX
354
HAZARD AVOIDANCE
NOTE: If the system has not received all available Regional Radar Precipitation data (such as during
initial FIS-B signal aquisitiation), the sytem may temporarily display areas of no radar coverage which are
subsquently removed as radar data is received. It may take up approximately ten minutes to receive all
FIS-B data.
ReFlectivity
Reectivityistheamountoftransmittedpowerreturnedtotheradarreceiver.ColorsontheNEXRAD
displayaredirectlycorrelative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NEXRADechointensitiesaremeasuredindecibels(dB)relativetoreectivity(Z).NEXRAD
measures the radar 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.
neXRaD limitatiOns
NEXRADradarimagesmayhavecertainlimitations:
•NEXRADbase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.
•NEXRADbasereectivityissampledattheminimumantennaelevationangle.AnindividualNEXRAD
sitecannotdepicthighaltitudestormsatcloseranges.Ithasnoinformationaboutstormsdirectlyover
the radar site.
•Whenzoomedintoarangeof30nm,eachsquareblockonthedisplayrepresentsanareaoffoursquare
kilometers.Theintensitylevelreectedbyeachsquarerepresentsthe
highest
levelofNEXRADdata
sampledwithinthearea(Figure6-106).