Ground Returns; Angle Of Incidence - Garmin GTN 725 Pilot's Manual

12.3.2.2
Foreword
The intensity of ground target returns depends upon the angle at which the
Getting
radar beam strikes the ground target (Angle of Incidence) and the reflective
Started
properties of that target. The gain can be adjusted so shorelines, rivers, lakes,
Audio &
and cities are well defined. Increasing gain too much causes the display to fill in
Xpdr Ctrl
between targets, thus obscuring some landmarks.
Com/Nav
Cities normally provide a strong return signal. While large buildings and
structures provide good returns, small buildings can be shadowed from the
FPL
radar beam by the taller buildings. As the aircraft approaches, and shorter ranges
are selected, details become more noticeable as the highly reflective regular lines
Direct-To
and edges of the city become more defined.
Proc
Bodies of water such as lakes, rivers, and oceans are not good reflectors,
and normally do not provide good returns. The energy is reflected in a forward
Charts
scatter angle with inadequate energy being returned. They can appear as dark
areas on the display. However, rough or choppy water is a better reflector and
Wpt Info
will provide stronger returns from the downwind sides of the waves.
Mountains also provide strong return signals to the antenna, but also block
Map
the areas behind. However, over mountainous terrain, the radar beam can be
Traffic reflected back and forth in the mountain passes or off canyon walls using up all
or most of the radar energy. In this case, no return signal is received from
Terrain
this area causing the display to show a dark spot which could indicate a
pass where no pass exists.
Weather
12.3.2.3
Nearest
The angle at which the radar beam strikes the target is called the Angle of
Incidence. Incident angle ("A") is illustrated below. This directly affects the
Services/
detectable range, the area of illumination, and the intensity of the displayed target
Music
returns. A large incident angle gives the radar system a smaller detectable range
Utilities
and lower display intensity due to minimized reflection of the radar energy.
System
Messages
Symbols
Appendix
12-36
Index

Ground Returns

Angle of Incidence

GTN 725/750 Pilot's Guide 190-01007-03 Rev. C