Furuno 821, 841 manual Nautical Chart and Radar Picture, Blind and shadow sectors

Blind and shadow sectors

Funnels, stacks, masts, or derricks in the path of antenna may reduce the intensity of the radar beam. If the angle subtended at the scanner is more than a few degrees a blind sector may be produced. Within the blind sector small targets at close range may not be detected while larger targets at much greater ranges may be detected. See Figure 3-7.

3.6Nautical Chart and Radar Picture

Under normal conditions, a picture which is similar to a nautical chart can be obtained on the radar display. However, a radar can- not:

•	show targets which are below the hori-
	zon.
•	show a target which is hidden by a larger
	one.

Vessel taller than wharf

Wharf

Wharf

Blind sector (no echo)

Mast, etc. in path of radar beam

Size of blind sector depends on target size and range.

• see around corners (for example, sea-

wall).

• distinguish between two targets which are

very close together, either in range or

bearing. For example, a vessel towing

another will probably appear as one ves-

sel, as both will be covered by the beam

at the same time.

The nautical chart and radar picture shown in Figure 3-8 are from the Kada Inland Sea in southwestern Japan.

Figure 3-7 Blind and shadow sectors

Black areas are strong reflection targets.

Coastline difficult to display.

Actual topography Radar display

Figure 3-8 Nautical chart and associated

radar picture

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