Garmin Flight Deck 100 Manual De Usuario

®

190-00728-04 Rev. A

358

Both Airborne Weather Radar and NEXRAD measure weather reflectivity in decibels (dB). A decibel is a

logarithmic expression of the ratio of two quantities. Airborne Weather Radar measures the ratio of power
against the gain of the antenna, while NEXRAD measures the energy reflected back to the radar, or the radar
reflectivity ratio.

Both systems use colors to identify the different echo intensities, but the colors are not interchangeable.

Airborne color radar values used by Garmin Airborne Color Weather Radar should not be confused with
NEXRAD radar values.

The radar beam is much like the beam of a spotlight. The further the beam travels, the wider it becomes.

The radar is only capable of seeing what is inside the boundaries of the beam. The figure below depicts
a  radar  beam’s  characteristics.    The  figure  illustrates  vertical  dimensions  of  the  radar  beam,  although  the
same holds true for the horizontal dimensions. In other words, the beam is as wide as it is tall. Note that
it is possible to miss areas of precipitation on the radar display because of the antenna tilt setting. With the
antenna tilt set to zero in this illustration, the beam overshoots the precipitation at 15 nautical miles.

0 

80 

Altitude (x1000 ft.) 

30 

0 

45 

60 

75 

90 

Range (nautical miles) 

Half Power at Beam Sidelobes

 

Antenna at Zero Tilt 

18,000 ft. 
18,000 ft. 

Max Power at Beam Center 

15 

8° 

The curvature of the earth can also be a factor in missing areas of precipitation, especially at range settings

of 150 nautical miles or more. Here the beam overshoots the precipitation at less than 320 nautical miles.

320 nm