SeaBat Sonar UI - User Manual
Operation
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4.3.8 Spreading
The spreading allows the operator to enter the amount of cylindrical and
spherical spreading loss that is expected through the ambient water
medium. Spreading of sound through water may be the greatest
contributor to the loss of sound. As sound moves away from its source in
all directions, the acoustic pressures will decrease with the range.
This value is used in conjunction with the absorption loss value (see
above) to compute the TVG (time varied gain) curve that is applied to the
returned signal (see Gain on page 24).
In practical situations the transmission loss will lie between 20 and 40dB;
in other words, the spreading loss will neither be perfectly spherical nor
perfectly cylindrical. Finally, if the sonar operates very close to the seabed
or very close to objects in general, near-field effects may yield a
transmission loss less than 20dB.
If the exact spreading loss value is not known, an initial value of 30dB is
recommended.
Figure 4-28
Spreading
4.3.9 Sound Velocity
When the override checkbox is checked, the sound velocity slider allows
the operator to enter a value for speed of sound in the water.
When a sound velocity sensor is interfaced and the override checkbox is
not checked the sound velocity value as displayed will be the value as
received from the sensor.
Figure 4-29
Sound velocity with Override checkbox
An online sound velocity must be used for providing up-to-date velocities
to ensure optimum performance. A manual velocity may be entered
instead but care should be taken to ensure the value entered is
representative of the real velocity.
4.3.10 SVP Filter
The sonar used the value from the sound velocity probe to present the
data in the wedge. When there are spikes in the data from the sound
velocity probe the display of the sonar data will be disturbed. The SVP
filter will filter these spikes out of the data. From a light filter (option Light)
to normal and a strong filter (option Wizard).
Figure 4-30
Sound velocity with Filter set to Normal
