How to open
NoteEach sonar application has its own TVG profile. Before changing the TVG settings, start the sonar (click ), then select the sonar application you want to configure from the Sonar applications list.
If you are using a high-frequency M3 Sonar, the TVG profiles will not be saved when closing the software — default values will apply when switching to a new frequency
or when starting up the M3 software.
Click the TVG button. This button is located on the tool bar.
Description
When an acoustic pulse is sent through the water, it will gradually lose its energy. The greater the distance between the transducer and the target(s), the greater the loss of energy.
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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.
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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 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.