FINE TUNING THE PICTURE
This chapter provides the information necessary for tuning the sonar picture. All operations are performed on sub panel 2 (data setting window).
Sub Panel 2
Figure 3-1 Display unit
Eliminating Unwanted Feeble Echoes
Echoes from targets such as seabed and fish return to the trans- ducer in order of distance to them, and when we compare their intensities at the transducer face, those from nearer targets are generally stronger when their reflecting properties are nearly equal. The sonar operator will be quite inconvenienced if these echoes are directly displayed on the screen, since he can not judge the actual size of the target from the size of echoes dis- played on the screen. To overcome this inconvenience, the TVG function is incorporated. It compensates for propagation loss of sound in water; amplification of echoes on short range is sup- pressed and gradually increased as range increases so that simi- lar targets are displayed in the similar intensities irrespective of the ranges to them.
The
