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ACTIVE SONAR USAGE
SeaBat T-Series Subsea Operator's Manual Page 40 January 31, 2019
Version 7

Adaptive Gates: Forces bottom detection to occur around the seabed profile within
an adaptive gating window typically set to 15-20% (of depth). This value should be
increased over rougher terrain or over a rapidly changing sea floor where bathymetry
is extreme in the vertical values.
6.2.10.1 Depth Gates
Use of a motion sensor is required to rotate the depth gates with the rolling motion of the vessel
to ensure soundings are not clipped as the seabed rotates with respect to the sonar.
The depth gates, with no input from a motion sensor, will orient themselves parallel to the
horizontal plane of the sonar head, as shown by the Min and Max Depth lines in
Figure 10 . In this
series of illustrations, the bottom detect dots are shown as a horizontal line (Line A or B) with
dashed lines representing depth gates above and below the bottom and no vessel roll present.
Visualize the bottom as being in the ‘layer’ formed by the depth gates.
MinDepth
MaxDepth
Line A
Sonar head
Figure 10: Depth Gates, With No Roll
Figure 11 shows the same bottom image with a small roll value to port. Notice that the ends of the
swath have been cut off due to the action of the static depth gates (no motion sensor applied). In
this figure, and all remaining figures in this discussion, the bottom is flat.