190-00498-07 Rev. A
Garmin G1000 Pilot’s Guide for Cessna Nav III
SYSTEM
OVERVIEW
FLIGHT
INSTRUMENTS EIS AUDIO PANEL
& CNS
FLIGHT
MANAGEMENT
HAZARD
AVOIDANCE AFCS ADDITIONAL
FEATURES APPENDICES INDEX
327
HAZARD AVOIDANCE
No Radar Coverage
Figure 6-69 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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.
•Radarbase reectivityis sampledat theminimum antennaelevation angle. 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.