4. FALSE ECHOES
Occasionally false echoes appear on the screen at positions where there is no target. In some cases the effects can be reduced or eliminated.
sented on both sides of the true echo at the same range, as shown in Figure
The operator should familiarize himself or her- self with the appearance and effects of these false echoes, so as not to confuse them with echoes from legitimate contacts.
True echo
4.1 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 echoes may be observed on the display at double, triple or other multiples of the actual range of the tar- get as shown in Figure
True echo
Own ship
Multiple
echo
Figure 4-1 Multiple echoes
4.2 Side-lobe Echoes
Every time the antenna rotates, some radiation escapes on each side of the
Sprious target
Antenna
Figure 4-2 Side-lobe echoes
4.3 Indirect Echoes
Indirect echoes may be returned from either a passing ship or returned from a reflecting sur- face on your own ship, for example, a stack. In both cases, the echo will return from a legiti- mate contact to the antenna by the same indi- rect path. The echo will appear on the same bearing of the reflected surface, but at the same range as the direct echo. Figure
•they usually occur in a shadow sector
•they appear on the bearing of the obstruc- tion but at the range of the legitimate con- tact
•when plotted, their movements are usually abnormal, and
•their shapes may indicate they are not direct echoes.
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