Standard Horizon MDS-8 Characteristics of Radar Wave, Targets difficult to display on screen

Beam

Side lobe

Main

Side

Antenna

Figure A.0.1 - Antenna pattern

A.1 CHARACTERISTICS OF RADAR WAVE

Radio waves travel out from the antenna while bending slightly along the earth’s surface. The amount they bend depends on atmospheric conditions. The sight distance of a radar generally is about 6% longer than the optical sight distance and is calculated using this

equation: Radar sight distance (NM) = 2.22 ( antenna height (m) + target height (m))

		Line of sight
		Radar Radio Wave
h1	Earth	h2

Figure A.1 - Radar wave

A.1.0 Targets difficult to display on screen

The intensity of the reflected radio signal from a target depends on the distance, height, and size of the target, as well as its material and shape, along with the radar’s transmitter power output and antenna size. Targets made of fibreglass, wood, or other low-reflectance materials or those that have a small incident angle are difficult to display on a screen. Sandy beaches, and sandy or muddy shallows can be difficult to catch. Because there’s not much to reflect a signal back to you, a coastline can actually be closer to your boat than it appears on the screen.

Invisible		3
	Apparent coastline	1
		HU
	Visible
	Actual (invisible)
	coastline

Figure A.1.0 - Targets difficult to display on screen

A.1.1 Shadow zones of radar

Radar waves propagate in a straight line. A high outcropping of land or a large ship will

Page 32 Radar Installation Manual