Garmin G1000 Pilot’s Guide for the Socata TBM 850
190-00709-00 Rev. A
6-12
HAZARD AVOIDANCE
R
EFLECTIVITY
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.
NEXRAD L
IMITATIONS
NEXRAD radar images may have certain limitations:
• NEXRAD base reflectivity does not provide sufficient information to determine cloud layers or precipitation
characteristics. 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. It has no information about storms directly over
the site.
• When zoomed in to a range of 30 nm, each square block on the display represents an area of four square
kilometers. The intensity level reflected by each square represents the highest level of NEXRAD data
sampled within the area.
Figure 6-11 NEXRAD Data - Zoomed
Each block
covers an Area
of 4 sq. km
