Garmin aera 500 - Manual (Page 93)

Garmin aera 500 Series Pilot’s Guide 190-01117-02 Rev. A
81
hazard avoidance
Overview
GPS Navigation
Flight Planning
Hazar
d
Avoidance
Additional F
eatur
es
Appendices
Index
neXrAD A
bnorMAlItIeS
There are possible abnormalities regarding displayed NEXRAD images. Some, but
not all, of those include:
• Ground clutter
• Strobes and spurious radar data
• Sun strobes, when the radar antenna points directly at the sun
• Military aircraft deploy metallic dust (chaff) which can cause alterations in radar
scans
• Interference from buildings or mountains, which may cause shadows
neXrAD l
IMItAtIonS
Certain limitations exist regarding the NEXRAD radar displays. Some, but not all, are
listed for the user’s awareness:
• NEXRAD base reflectivity does not provide sufficient information to determine
cloud layers or precipitation characteristics (hail vs. rain). For example, it is not
possible to distinguish between wet snow, wet hail, and rain.
• NEXRAD base reflectivity is sampled at the minimum antenna elevation angle. An
individual NEXRAD site cannot depict high altitude storms at close ranges, and
has no information about storms directly over the site.
• Radar coverage only extends to 55°N.
• Any precipitation displayed between 52°N and 55°N is unknown.
neXrAD I
ntenSIty
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.