Kongsberg Flexview, Reference Manual

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922-20207001/1.0
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Description
When an acoustic pulse is sent through the water, it will gradually lose its energy. The
greater the distance between the Sonar Head and the target(s), the greater the loss
of energy.
•
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).
•
Absorption loss
Depending on the salinity and temperature, the water will absorb some of the energy
from the 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 Varible Gain) compensation is designed to counteract the natural
phenomena of geometric spread and absorption loss. In the Flexview, 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 Sonar Head.
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
Functions and dialog boxes