Finding Range And Bearing To A Target; Eliminating Weak Echoes - Furuno FSV-24 Operator's Manual

2. HORIZONTAL MODE
2.5

Finding Range and Bearing to a Target

Operate the trackball to place the trackball mark on the target you want to
measure the range and bearing. The range, bearing and depth to the target
appear at the upper left corner of the screen.
2.6

Eliminating Weak Echoes

Echoes from targets such as bottom and fish return to the transducer 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 displayed on the screen. To overcome
use the TVG function. It compensates for propagation loss of sound in water;
amplification of echoes on short range is suppressed and gradually increased as
range increases so that similar targets are displayed in the similar intensities
irrespective of the ranges to them.
The FSV-24 has three TVG functions, NEAR, MEDIUM and FAR, and they
mainly compensate for propagation loss on short, middle and long ranges
respectively, centered at the ranges shown below. The higher the TVG setting
the greater the amplification of echoes.
The TVG is also used to suppress unwanted echoes and noise which appear in
2-8
TRACKBALL DATA
Slant range
î
Horizontal range
è
Depth
ê
B Relative or
True bearing*
*True bearing requires
appropriate sensor.
Figure 2-8 Location of trackball data
Figure 2-9 Principle of TVG
î
è
ê
B
Trackball mark
34 56.789N
°
Trackball mark
123 45.678E
°
position