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PRINCIPLE OF OPERATION
AP-6
PRINCIPLE OF OPERATION
When a moving vessel emits an acoustical pulse into the water at an angle, a portion of the
emitted energy is reflected from the bottom and other microscopic objects in the sound path,
such as plankton or air bubbles. The frequency of the received signal is shifted from the
transmitted frequency in proportion to the relative velocity between the vessel and
underwater reflecting objects. This is called the Doppler Effect.
This equipment calculates and displays movements of ship and currents at specific depths
by measuring Doppler shifts obtained from three separate directions.
Plankton layer
Bottom
Frequency of reflected signal is
shifted in proportion to relative speed
between the vessel and reflecting
objects.