Koden ESR-145, Operation Manual

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SONAR SYSTEM SUMMARY
SONAR MODE
A sonar system uses the transmitter-receiver as well as an echo sounder.
An echo sounder is only able to search in one direction, down.
However, a sonar has a movable transducer and therefore can freely search the entire
around a ship, not just the area directly beneath the ship.
When the sonar is not operated, the transducer is retracted.
While operating, the transducer is protruded from the hull bottom.
An ultrasonic pulse is emitted from the transducer protruded from the hull bottom.
The sonar principle detected by the transducer is the same with the echo sounder.
However, like a searchlight, the sonar transducer sends and detects ultra-sound
beams one after another while giving relative bearing at some speed in proper ranges.
The transducer scans or trains with the step angle set at MENU.
The seabed and fish school will send a reflected echo of sound back to the ship.
In a PPI sonar, this reflection with relative bearing and range information is presented
like a radar screen.
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