How To Read Sonar Data; Sonar Beam - Marine Sea Scan Manual

The operator can view wide tracts of the seafloor because the transducers ping along the swath
width and the software records the strength of the echoes from the sea bottom. The towfish is
towed just above the seafloor bottom. The transducers continuously emit narrowly focused beams
of sound perpendicular to the path of motion. The sound pulses pass through the water but are
reflected from the seafloor and objects, such as wreck sites that sit on the seafloor. The computer
records the echo signal strengths as they return and draws the entire SONAR record line on the
screen. Thus, an image is built, line by line, as the SONAR record line from each ping returns and
is drawn on the screen.
The quality of the SONAR data will depend on operator and the data-gathering process, which
involves vessel course, tow speed, towfish altitude above the bottom, sea conditions, and range
settings. For example, a higher range setting yields a larger data sample with more of the seafloor
displayed; but the data will not have as high a resolution.
2.2.1

How to Read SONAR Data

2.2.1.1

SONAR Beam

Vertical Beam Angle
How wide the beam angle is; it is measured from the sea bottom to the top of the sound that was
projected from the transducer.
Horizontal Beam Width
The width of the sound wave determines the expanse of the area covered horizontally, and the
speed of the boat determines the ping spacing. The slower the vessel moves, the more
overlapping coverage that will be obtained. This approach yields more data for a higher quality
image.
© 2013 Marine Sonic Technology, Ltd.
Introduction to Side Scan SONAR
The vertical beam angle
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