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3. TARGET TRACKING (TT)
3-11
3.9 Vector Modes
Target vectors can be displayed relative to own ship's heading (Relative) or North
(True).
Note: IMO recommends the use of the true vector mode in sea stabilization or relative
vector mode for collision avoidance.
3.9.1 Description of vectors
Stabilization modes
It is important to select the optimum stabilization mode for the radar display. To assess
risk of collision the relative motion of a target gives the clearest indication of CPA and
may be monitored by observing either the direction of the target's relative trail, or the
CPA predicted by the relative vector. By default, relative motion displays relative target
trails and true motion displays true target trails. Where true target trails is selected, a
sea stabilized display will indicate all targets' motion through the water. A ground sta-
bilized display will indicate all targets' motion over the ground.
In coastal, estuarial and river waters where a significant set and drift may be experi-
enced, a sea stabilized display will produce significant target trails from all fixed (sta-
tionary) objects possibly producing an unacceptably high level of clutter and masking.
In such circumstances a ground stabilized display may reduce its effect and enable
the observer to detect clearly the trails of moving targets, thus enhancing the observ-
er's situational awareness.
However, the display should be considered only as an approximation of the course
and speed made good over the ground. Among other factors, the accuracy of the
ground-stabilization is affected by inaccuracies in speed and heading inputs as well
as radar measurement imprecision and will require the display to be readjusted peri-
odically. The information displayed should be interpreted with due regard to these fac-
tors.
Note: It should be noted that in determining a target's aspect by radar; the calculation
of its true track is dependent on the choice and accuracy of the own ship's course and
speed input. A ground-stabilized target plot may accurately calculate the ground track
of the target, but the target's heading may be significantly different from its track when
experiencing set, drift or leeway. Similarly, a sea stabilized target plot may be inaccu-
rate when own ship and the target, are experiencing different rates of set, drift or lee-
way.
Ground stabilization and sea stabilization
Target vectors can be ground stabilized or sea stabilized in the True Motion mode. To
select speed over the ground or speed through the water data, open the page from the
menu. Select for ground stabilization or for sea stabilization. The Vector mode indica-
tion shows the stabilization mode in the true motion as [True-G] or [True-S].
Sea stabilization is a mode where own ship and all targets are referenced to the sea
using a compass heading and single-axis log water speed inputs in the true motion
mode. Ground stabilization is a mode where own ship and all targets are referenced
to the ground using the ground track or set and drift inputs. If the accuracy seems un-
satisfactory, enter set and drift corrections. Note that set and drift should not be used
when the radar is displaying AIS targets.