Garmin HTAWS User Guide - Page 21

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Part Two: Section 2 XM Weather NEXRAD Intensity Colors are used to identify the different NEXRAD echo intensities (reflectivity) measured in dBZ (decibels of Z). "Reflectivity" is the amount of transmitted power returned to the radar receiver. Reflectivity (designated by the letter Z) covers a wide range of signals (from very weak to very strong). So, a more convenient number for calculations and comparison, a decibel (or logarithmic) scale (dBZ), is used. The dBZ values increase as the strength of the signal returned to the radar increases. There are seven gradations for rain, two gradations for mixed rain and snow, and two gradations for snow. To display the NEXRAD Intensity Legend: 1. While viewing the XM Weather page, press the MENU key to display the Page Menu. 2. Turn the large or small knob to select "Display legend?" 4. Turn the large or small knob to scroll through the full table. Press CLR to return to the normal view. 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 3. Press ENT to display the NEXRAD Intensity Legend. 190-00356-30 Rev H 15

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15
Part Two: Section 2
XM Weather
NEXRAD Intensity
Colors are used to identify the different NEXRAD
echo intensities (reflectivity
) measured in dBZ (deci
-
bels of Z). “Reflectivity” is the amount of transmitted
power returned to the radar
receiver. Reflectivity
(designated by the letter Z) covers a wide range of
signals (from very weak to very strong). So, a more
convenient number for calculations and comparison, a
decibel (or logarithmic) scale (dBZ), is used. The dBZ
values increase as the strength of the signal returned
to the radar increases. There are seven gradations for
rain, two gradations for mixed rain and snow, and two
gradations for snow.
To display the NEXRAD Intensity Legend:
1.
While viewing the XM Weather page, press the
MENU
key to display the Page Menu.
2.
Turn the
large
or
small
knob to select “Display
legend?”
3.
Press
ENT
to display the NEXRAD Intensity
Legend.
4.
Turn the
large
or
small
knob to scroll through
the full table. Press
CLR
to return to the normal
view.
NEXRAD Abnormalities
There are possible abnormalities regarding dis-
played 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
190-00356-30 Rev H