Garmin G1000 NXi Pilot's Manual page 268

HAZARD AVOIDANCE
4) Turn the small FMS Knob to select 'US' or 'CNDA', then press the ENT Key.
5) To remove the menu, push the FMS Knob or the CLR Key.
The NEXRAD weather product age display indicates either 'US' or 'CN' for the selected coverage region.
r
efleCTIvITy
Reflectivity is the amount of transmitted power returned to the radar receiver. Colors on the NEXRAD
display are directly correlative 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
letter Z). The value of Z increases as the returned signal strength increases.
neXraD l
IMITaTIonS
NEXRAD radar images may have certain limitations:
• Undetermined precipitation types may be displayed as mixed.
• An individual NEXRAD site cannot depict high altitude storms at close ranges. It has no information
about storms directly over the site.
• Precipitation may be occurring below the lowest antenna tilt angle (0.5º), and therefore the radar beam
overshoots the precipitation. For example, at a distance of 124 miles from the radar site, the radar beam
is approximately 18,000 feet above the radar site. The radar cannot detect any precipitation occurring
below the beam at this distance and altitude.
• At smaller map ranges, the smallest square block on the display represents an area of approximately
four square kilometers. The intensity level reflected by each square represents the highest level of radar
reflectivity sampled within the area.
• Unknown precipitation below 52ºN is displayed as rain regardless of actual precipitation type.
254 Garmin G1000 NXi Pilot's Guide for the Cessna Nav III
back to
the radar receiver (designated by the
190-02177-00 Rev. A