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11-9190-01004-03 Rev. B
Garmin GTN 625/635/650 Pilot’s Guide
Foreword
Getting
Started
Xpdr Ctrl
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Proc
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Map
Traffic
Terrain
Weather
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Appendix
Index
Figure 11-8 NEXRAD Weather Legend
11.1.5.1 Reflectivity
Reflectivity is the amount of transmitted power returned to the radar receiver.
Colors on the NEXRAD display directly correlate to the level of detected
reflectivity. Reflectivity as it relates to hazardous weather can be very complex.
The role of radar is essentially to detect moisture in the atmosphere. Simply
put, certain types of weather reflect radar better than others. The intensity of a
radar reflection is not necessarily an indication of the weather hazard level. For
instance, wet hail returns a strong radar reflection, while dry hail does not. Both
wet and dry hail can be extremely hazardous.
The different NEXRAD echo intensities are measured in decibels (dB) relative
to reflectivity (Z). NEXRAD measures the radar reflectivity ratio, or the energy
reflected back to the radar receiver (designated by the letter Z). The value of Z
increases as the returned signal strength increases.