Definition
Erroneous depth indications arising when a return from one transmission arrives after the next pulse has been sent, when the transducer detects fish shoals, aeration, thermoclines, a soft mud layer or the vessel's own wake, or when the display locks onto a strong side lobe return. In deep water a second trace can show a fraction of the true depth. Cross checking against the charted depth, the trend of successive soundings and a graphical echogram display, rather than a bare digital figure, helps identify them.
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