Kongsberg Simrad ST90, Reference Manual

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RCG (Reverberation Controlled Gain) function, page 484
Bottom Filter Threshold function, page 487
Noise Filter function, page 488
Horizontal Scroll function, page 490
Vertical Reference function, page 491
Echogram dialog box, page 492
Information Pane Options dialog box, page 492
TVG function
TVG
(Time Variable Gain) compensates for the loss of acoustic energy due to geometric
spread and absorption. This makes the targets with the same strength appear with the same
intensity independent of their physical distance from the transducer.
How to open
This function is opened from the
Active
menu.
Description
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. In the ST90 system, the
TVG compensation is made using digital signal processing software.
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.
The loss of energy is explained with two factors.
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.
Functions and dialog boxes