Sec 6 Sec 5 Sec 4

 

curvature of the earth can also be a factor, especially at range settings of 150 NM

Foreword

or more.

 

 

 

Sec 1 System

 

NM

 

 

Sec 2 PFD

Figure 4-68

Radar Beam in Relation to the Curvature of the Earth

 

 

4.10.1.3Radar Signal Attenuation

Sec 3 MFD

The phenomena of weather attenuation needs to be kept in mind whenever

operating the weather radar. When the radar signal is transmitted, it is

 

 

progressively absorbed and scattered, making the signal weaker. This weakening,

Hazard

Avoidance

or attenuation, is caused by two primary sources, distance and precipitation.

Attenuation because of distance is due to the fact that the amount of radar

 

 

 

 

energy at a distance from the antenna is inversely proportional to the square of

Additional

Features

the distance. The reflected radar energy from a target 40 miles away that fills

the radar beam will be one fourth the energy reflected from an equivalent target

 

 

 

 

20 miles away. This would appear to the operator that the storm is gaining

Annun. Alerts&

intensity as the aircraft gets closer. Internal circuitry within the GWX 68 system

compensates for much of this distance attenuation.

 

 

 

 

Attenuation due to precipitation is not as predictable as distance attenuation.

Sec7 Symbols

It is also more intense. As the radar signal passes through moisture, a portion of

the radar energy is reflected back to the antenna. However, much of the energy is

 

 

 

 

absorbed. If precipitation is very heavy, or covers a large area, the signal may not

Sec8 Glossary

reach completely through the area of precipitation. The weather radar system

cannot distinguish between an attenuated signal and area of no precipitation.

 

 

 

 

If the signal has been fully attenuated, the radar will display a “radar shadow.”

 

A

This appears as an end to the precipitation when, in fact, the heavy rain may

 

Appendix

extend much further. A cell containing heavy precipitation may block another

 

cell located behind the first, preventing it from being displayed on the radar.

B

 

Never fly into these shadowed areas and never assume that all of the heavy

 

precipitation is being displayed unless another cell or a ground target can be

Appendix

Index

seen beyond the heavy cell. The WATCH™ feature of the GWX 68 Weather

 

 

 

 

Radar system can help in identifying these shadowed areas. Areas in question

4-82

Garmin G600 Pilot’s Guide

190-00601-02 Rev. E

Page 242
Image 242
Garmin G600 manual Radar Signal Attenuation, Compensates for much of this distance attenuation