4-51190-01150-02 Rev. J Garmin G500H Pilot’s GuideForewordSec 1SystemSec 2PFDSec 3MFDSec 4HazardAvoidanceSec 5AdditionalFeaturesSec 6Annun.& AlertsSec 7SymbolsSec 8Glossary Appendix AAppendix BIndexThe display of radar coverage is always active when either NEXRAD orECHO TOPS is selected. Areas where NEXRAD radar coverage and Echo Topsinformation is not currently available or is not being collected are indicated ingrayish-purple.4.7.5.1 ReflectivityReflectivity is the amount of transmitted power returned to the radar receiver.Colors on the NEXRAD display directly correlate to the level of detectedreflectivity. Reflectivity as it relates to hazardous weather can be very complex.The role of radar is essentially to detect moisture in the atmosphere. Simplyput, certain types of weather reflect radar better than others. The intensity of aradar reflection is not necessarily an indication of the weather hazard level. Forinstance, wet hail returns a strong radar reflection, while dry hail does not. Bothwet and dry hail can be extremely hazardous.The different NEXRAD echo intensities are measured in decibels (dB) relativeto reflectivity (Z). NEXRAD measures the radar reflectivity ratio, or the energyreflected back to the radar receiver (designated by the letter Z). The value of Zincreases as the returned signal strength increases.4.7.5.2 NEXRAD LimitationsNEXRAD radar images may have certain limitations:• NEXRAD composite reflectivity does not provide sufficient informationto determine cloud layers or precipitation characteristics. For example, itis not possible to distinguish between wet snow, wet hail, and rain.• NEXRAD composite reflectivity is sampled at the minimum antennaelevation angle. An individual NEXRAD site cannot depict high altitudestorms at close ranges. It has no information about storms directly overthe site.• When zoomed in to a range of 30 NM, each square block on the displayrepresents an area of four square kilometers. The intensity level reflectedby each square represents the highest level of NEXRAD data sampledwithin the area.The following may cause abnormalities in displayed NEXRAD radar images:• Ground clutter• Strobes and spurious radar data• Sun strobes (when the radar antenna points directly at the sun)
