Manual

June 2004 Isis® Sonar User's Manual, Volume 2 152
Port/Stbd
channels
(continued)
Usually you aim the SeaBat with the center beam pointing straight
down. In this orientation, the port beam coincides with the ship’s port
side and the starboard beam coincides with the ship’s starboard.
The direction of each beam is unalterable with respect to the beam
next to it. However, you can shift the point of aim of the set of all three
beams together so that the trio points more to the port or more to the
starboard. By repositioning the SeaBat on its mounting plate, you can
achieve a more port-skewed or starboard-skewed aim. Angling the
beams in this way may help you optimize the scan pattern for your
intended data survey.
Installation
Offsets
A ship usually navigates using a primary positioning system, such as
GPS. Other devices on board ship use input from the positioning
system as part of their own output. If the devices, such as a SeaBat or
a motion reference unit (MRU), are far from the positioning system,
the reported position will be different from that of the devices. In such
cases, you need to let Isis know of this difference by specifying one or
more numerical offsets, in meters. You make these kinds of
corrections in the Installation Offsets text boxes in the SeaBat Setup
dialog box.
X-axis
To compensate for
across-track differences, type a number in the
X-axis offset box or boxes for each device affected. If the SeaBat
and/or MRU is to the starboard of the positioning system, enter the
across-track, positive offset (in meters) between the towfish and the
positioning system. If the SeaBat or MRU is to the port of the
positioning system, enter the negative offset (in meters) as the offset
between the fish and the positioning system. All offsets are relative to
an arbitrary reference point established by the user.
Y-axis
To compensate for
along-track differences, type a number in the
Y-axis offset box or boxes for each device affected. If the SeaBat
and/or MRU is forward of the positioning system, enter a positive
value as the along-track positive offset (in meters) between the
towfish and the positioning system. If the SeaBat or MRU is aft of the
positioning system, enter the negative value as the offset between the
fish and the positioning system. All offsets are relative to an arbitrary
reference point established by the user.
Appendix I: Working with Specific Sonars