Garmin Appliance Data User's Guide Page 77

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Affected Areas
Any area in the continental United States (CONUS) or
Alaska where the distance from ADS-B ground stations
or the combined effect of distance and low altitude is
sufficiently great to cause poor reception. A good source
of information 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 the NextGen ADS-B ground station
infrastructure. However, due to line-of-sight broadcast
characteristics, operators with properly installed and
functioning equipment may still receive incomplete FIS-B
data when signal reception is limited by the distance from
ground stations combined with a low altitude.
The example below displays an area where FIS-B data is
degraded due to poor reception:
Example of Areas Where FIS-B Reception Is Incomplete
NEXRAD Description
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 update rate is
2.5 minutes for Regional NEXRAD and 15 minutes for
CONUS NEXRAD.
NEXRAD Abnormalities
There are possible abnormalities regarding displayed
NEXRAD images. Some, but not all, causes of abnormal
displayed information include:
Ground Clutter
Strobes and spurious radar data
Sun strobes, when the radar antenna points directly
at the sun
Military aircraft deploy metallic dust which can
cause alterations in radar scans
Interference from buildings or mountains, which
may cause shadows
Scheduled maintenance may put a radar off-line
NEXRAD Limitations
Certain limitations exist regarding the NEXRAD
radar displays. Some, but not all, are listed for the user’s
awareness:
The (high resolution) Regional NEXRAD “pixels”
are 1.5 minutes (1.5 nautical miles = 2.78 km)
wide by 1 minute (1 nautical miles = 1.852 km)
tall. The (medium resolution – 5 times larger than
high resolution) CONUS NEXRAD “pixels” are 7.5
minutes (7.5 nautical miles = 13.89 km) wide by 5
minutes (5 nautical miles = 9.26 km) wide. Above
60 degrees of latitude the block widths double to
Part Seven: Section 2
GDL 88 Interface: FIS-B Weather
190-00356-30 Rev L
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