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Geometric spread
Once transmitted, the acoustic energy will spread out to form a circular beam. The width
of this beam increases with the physical distance to the target(s).
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Absorption loss
Depending on the salinity and temperature, the water will absorb some of the energy
from the acoustic transmission. The absorption loss increases as the physical distance
to the target(s) increases.
Both the geometric spread and the absorption will also have an effect on the returned echo
signal. That is why we normally refer to these factors as the two-way transmission loss.
The TVG (Time Variable Gain) compensation is designed to counteract the natural
phenomena of geometric spread and absorption loss. In the M3 Sonar FLS system, the TVG
compensation is made using digital signal processing software. By means of algorithms,
the time variable gain compensation converts the echo presentation as a function of range.
This makes the targets with the same strength appear with the same intensity independent of
their physical distance from the transducer.
Details
The TVG compensation is expressed as a logarithmic curve. You can choose from a
selection of curves. Each curve has a different slope creating a different gain compensation.
Four adjustable factors are used to set the gain curve.
A Factor
Represents spreading loss.
B Factor
Represents one-way absorption loss.
C Factor
Represents a base or starting gain level.
L Factor
Limits the maximum gain to reasonable levels.
To the left of the TVG curve display is a slider with a range from -30 to 130. This represents
the system gain. Moving this slider down until the line intersects the green TVG curve will
cause a Range-Gain pair of values to be displayed in the “Range-Gain” box. Adjust this
slider to determine the gain at a particular range.
If you have a software license for advanced features, then an additional pane and slider
bar will become available. When the Sonar Head is running, a graphic representation of
the receive signal will appear at the bottom of the dialog box so that you can ensure that
the signal is not being clipped. A slider is provided so that you can exclude the low end
percent of the gain.
M3 Sonar FLS Reference Manual
Summary of Contents for M3 Sonar
Page 1: ...Reference Manual M3 Sonar FLS Forward Looking Multibeam sonar ...
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