190-00962-02 Rev. A
Garmin G1000 Pilot’s Guide for the Diamond DA42NG
353
HAZARD AVOIDANCE
SY
STEM
O
VER
VIEW
FLIGHT
INSTRUMENTS
EIS
AUDIO P
ANEL
& CNS
FLIGHT
MANA
GEMENT
HAZARD
AV
OID
ANCE
AFCS
ADDITIONAL
FEA
TURES
APPENDICES
INDEX
NOTE:
If the system has not received all available Regional Radar Precipitation data (such as during
initial FIS-B signal acquisition), the system may temporarily display areas of no radar coverage which are
subsequently removed as radar data is received. It may take up approximately ten minutes to receive all
FIS-B data.
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
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 (wet hail vs. rain). 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 radar 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 6-105).
