Garmin GDL 88 User Manual

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5-2
GDL 88 ADS-B Transceiver Pilot’s Guide
190-01122-03  Rev. A
  WARNING:  Do not use the indicated data link weather product age to 
determine the age of the weather information shown by the data link weather 
product. Due to time delays inherent in gathering and processing weather 
data for data link transmission, the weather information shown by the data 
link weather product may be significantly older than the indicated weather 
product age. 
5.1 FIS-B 
NEXRAD
WSR-88D weather surveillance radar or NEXRAD (NEXt generation RADar) is
a Doppler radar system that has greatly improved the detection of meteorological 
events such as thunderstorms, tornadoes, and hurricanes. An extensive network 
of NEXRAD stations provides almost complete radar coverage of the continental
United States, Alaska, and Hawaii. The unobstructed range of each NEXRAD is
124 nautical miles. 
The FIS-B Function is a graphic weather display capable of displaying graphical 
weather information on UAT equipped installations. Graphical data is overlaid on
the map indicating the rainfall detected by ground based radar for a specific area. 
Colors are used to identify the different NEXRAD echo intensities (reflectivity)
measured  in  dBZ  (decibels  of  Z).  “Reflectivity”  (designated  by  the  letter  Z)  is
the amount of transmitted power returned to the radar receiver. The dBZ values
increase as returned signal strength increases. Precipitation intensity is displayed 
using colors corresponding to the dBZ values. An example of how precipitation
data is color coded follows: 
Figure 5-1  Sample FIS-B Weather Precipitation Legend