11-54Garmin GTN 625/635/650 Pilot’s Guide 190-01004-03 Rev. KForewordGettingStartedAudio &Xpdr CtrlCom/NavFPLDirect-ToProcWpt InfoMapTrafficTerrainWeatherNearestServices/MusicUtilitiesSystemMessagesSymbolsAppendixIndex11.4.2.3 NEXRAD IntensityColors are used to identify the different NEXRAD echo intensities (reflectivity)measured in dBZ (decibels of Z). “Reflectivity” is the amount of transmitted powerreturned to the radar receiver. Reflectivity (designated by the letter Z) covers awide range of signals (from very weak to very strong). So, a more convenientnumber for calculations and comparison, a decibel (or logarithmic) scale (dBZ),is used. The dBZ values increase as the strength of the signal returned to theradar increases.11.4.2.4 NEXRADWhen enabled, NEXRAD weather information is shown. Composite datafrom all of the NEXRAD radar sites in the United States is shown. This data iscomposed of the maximum reflectivity from the individual radar sweeps. Thedisplay of the information is color-coded to indicate the weather level severity.Refer to the legend for a description of the color code.The NEXRAD option has selections of Regional, CONUS, or CombinedNEXRAD. CONUS NEXRAD includes a composite of available NEXRAD radarimagery across the 48 states. Regional NEXRAD is a composite of availableNEXRAD radar imagery in a local area, showing a more detailed imagethan CONUS NEXRAD. FIS-B weather data reception requires line-of-sitecommunication between the receiver and the ADS-B ground station. IncompleteRegional and/or CONUS NEXRAD imagery displayed on the MAP and FIS-BWeather Pages of the affected products is an indicator of poor FIS-B reception.Affected AreasAny area in the continental United States (CONUS) or Alaska where thedistance from ADS-B ground stations, or the combined effect of distance andlow altitude, is sufficiently great may cause poor reception. A good source ofinformation for ground station coverage can be found at:http://www.faa.gov/nextgen/flashmap/Reception will improve in some affected areas as the FAA completes theNextGen ADS-B ground station infrastructure. However, due to line-of-sightbroadcast characteristics, operators with properly installed and functioningequipment may still receive incomplete FIS-B data when signal reception islimited by the distance from ground stations combined with a low altitude.
