Garmin Appliance Data User's Guide download pdf (Page 111)

99190-00607-02 Rev D

Detailed Operation

Radar

unless another cell or a ground target can be seen

beyond the heavy cell.

Radar Signal Reﬂectivity

Precipitation

Precipitation or objects more dense than water,

such as earth or solid structures, will be detected by

the weather radar. The weather radar will not detect

clouds, thunderstorms or turbulence directly. It detects

precipitation associated with clouds, thunderstorms,

and turbulence. The best radar signal reﬂectors are

raindrops, wet snow or wet hail. The larger the rain-

drop the better it reﬂects. The size of the precipitation

droplet is the most important factor in radar reﬂectiv-

ity. Because large drops in a small concentrated area

are characteristic of a severe thunderstorm, the radar

displays the storm as a strong return. Ice, dry snow,

and dry hail have low reﬂective levels and often will

not be displayed by the radar. A cloud that contains

only small raindrops, such as fog or drizzle, will not

reﬂect enough radar energy to produce a measurable

target return.

Precipitation Type and Reﬂectivity

Ground Returns

The intensity of ground target returns depends

upon the angle at which the radar beam strikes the

ground target (Angle of Incidence) and the reﬂective

properties of that target. The gain can be adjusted so

shorelines, rivers, lakes, and cities are well deﬁned.

Increasing gain too much causes the display to ﬁll in

between targets, thus obscuring some landmarks.

Cities normally provide a strong return signal.

While large buildings and structures provide good

returns, small buildings can be shadowed from the

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 and edges of the city become more deﬁned.

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 scat-

ter 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 will

provide stronger returns from the downwind sides of

the waves.

Mountains also provide strong return signals to the

antenna, but also block the areas behind. However,

over mountainous terrain, the radar beam can be

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

this area causing the display to show a dark spot

which could indicate a pass where no pass exists.

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Garmin Appliance Data User's Guide Page 111

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