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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echo
Bridge
Indirect
Indirectecho echo
Figure 4-3 Indirect echoes
4.4Blind and Shadow Sectors
Funnels, stacks, masts, or derricks in the path of antenna may reduce the intensity of the ra- dar beam. If the angle subtended at the antenna is more than a few degrees a blind sector may be produced. Within the blind sector small tar- gets at close range may not be detected while larger targets at much greater ranges may be detected. See Figure
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