Appendix C: Sonar - Raymarine RayTech RNS 5.0 User Manual

Appendix C: Sonar

Introduction
The sonar provides a detailed underwater view that helps you to see bottom structure and
texture, underwater obstructions such as wrecks and fish. Depth data is also provided and
depth and temperature alarms can be set.
How the sonar works
The sonar application uses a Digital Sounder Module (DSM) to process sonar signals from
a suitable transducer and provide a detailed underwater view.
The transducer located on the bottom of the boat sends pulses of sound waves into the
water and measures the time it takes for the sound wave to travel to the bottom and back.
The returning sound echoes are affected by bottom structure and any other objects in their
path, e.g. wrecks, reefs and fish.
The DSM processes these echoes and sends data to the sonar which displays a visual
interpretation of the underwater view. The strength of echoes is indicated on the display
by different colors. You can use this information to determine the bottom structure, the
size of fish and other objects in the water, e.g. debris or air bubbles.
Notes: (1)
Bottom indications
The bottom usually produces a strong echo, enabling the sonar to see great detail.
A hard bottom, such as sand, produces a thin line.
A softer bottom covered with seaweed produces a wide line, as the sound waves reflect
from different layers of the bottom. In this image the sonar is getting a good echo from the
bottom, so the upper layer of the bottom is shown as dark gray.
The DSM will operate at a frequency of 50 kHz or 200 kHz.
Some transducers will enable the sonar to display water temperature and/or
(2)
speed data.
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