Furuno 841 MARK-2 manual Bearing Resolution, Range Resolution, False Echoes, Multiple echoes

On the other hand, hulls made from wood or fiberglass return much weaker echoes.

Vertical surfaces, such as a cliff, are good targets provided they face the radar. Con- versely, horizontal and smooth surfaces such as mudbanks, sandy beaches, and gently sloping hills make poor targets because they disperse rather than reflect most of the en- ergy that strikes them.

The strongest radar echoes known come from built-up areas, docks, etc., because these targets are less subject to changes in aspect. These types of targets have three flat,

3.4 Bearing Resolution

Bearing resolution is a measure of the ca- pability of a radar to display as separate tar- gets the echoes received from two targets which are at the same range and are close together.

The principal factor which affects bearing resolution is horizontal beamwidth. Two tar- gets at the same range must be separated by more than one beamwidth to appear as sepa- rate pips.

smooth surfaces mutually at right angles. Some radar buoys are arranged this way so as to deliberately increase their detection range.

3.3 Range Resolution

Range resolution is a measure of the capa- bility of a radar to display as separate pips

Target

Horizontal beamwidth

Direction of scanner rotation

Target

Radar is able to display two distinct target echoes.

the echoes received from two targets which are on the same bearing and are close to- gether.

The main factor which affects range resolu- tion is pulselength. Two targets on the same bearing, close together, cannot be seen as two distinct echoes on the display unless they are separated by a distance greater than one-half the pulselength.

Horizontal beamwidth

Direction of scanner rotation

Radar cannot display targets as separateechoes because they are within the beamwidth.

Figure 3-3 Bearing resolution

3.5 False Echoes

Transmitted radar pulse

Transmitted radar pulse

Radar is able to display two distinct target echoes.

Target

Target

Occasionally false echoes appear on the screen at positions where there is no target. In some cases the effects can be reduced or eliminated. The operator should familiarize himself or herself with the appearance and effects of these false echoes, so as not to confuse them with echoes from legitimate contacts.

Radar cannot display targets as separate echoes because they are within the pulselength.

Figure 3-2 Range resolution

Multiple echoes

Multiple echoes occur when a short range, strong echo is received from a ship, bridge, or breakwater. A second, a third or more ech-

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