1. Target means any object fixed or moving whose position and motion is
determined by measurements of range and bearing on radar.
2. Relative course means the direction of motion of a target relative to own
ship’s position expressed as an angular displacement from north. It is deduced from
a number of measurements of target range and bearing on own ship’s radar.
3. Relative speed means the speed of a target relative to own ship’s position.
It is deduced from a number of measurements of target range and bearing on own
ship’s radar.
4. Relative motion means the combination of relative course and relative
speed.
5. True course means the true direction of motion of a target expressed as an
angular displacement from north. It is obtained by a vector combination of target
relative motion and own ship’s true motion.footnote
6. True speed means the speed of a target obtained by a vector combination of
target relative motion and own ship’s true motion.footnote
7. True motion means the combination of true course and true speed.
8. True bearing means the direction of a target from own ship or from another
target expressed as an angular displacement from north.
9. Relative bearing means the direction of a target from own ship expressed as
an angular displacement from own ship’s heading.
10. True motion display means a display across which own ship and each target
moves with its own true motion.
11. Relative motion display means a display on which the position of own ship
remains fixed and all targets move relative to own ship.
12. Azimuth stabilized display means a display in which the azimuth
orientation relative to a nominated true bearing is fixed.
13. North-up display means an azimuth stabilized display in which a line
connecting the centre with the top of the display is north true bearing.
14. Course-up display means an azimuth stabilized display in which a line
connecting the centre with the top of the display is own ship’s intended course.
15. Heading means the direction in which the bows of a ship are pointing
expressed as an angular displacement from north.
16. Target’s predicted motion means a prediction of future target motion based
on linear extrapolation from its present motion as determined by past measurements
of its range and bearing on the radar.
17. Relative vector means the predicted movement of a target relative to own
ship.
18. True vector means the predicted true motion of a target as a result of own
ship’s direction and speed input. The true vector may be either displayed with
reference to the water or to the ground.
19. Acquisition means the process of selecting a target or targets and
initiating their tracking.
20. Tracking means the computer process of observing the sequential changes in
the position of a target in order to establish its motion.
21. Target swop means a situation in which the incoming radar data for a
tracked target becomes incorrectly associated with another tracked target or a
non-tracked radar echo.
22. Acquisition area means an area set up by the observer which should
automatically acquire a target when it enters such an area.
23. History means equally time-spaced past position of a target which is being
tracked. The history may be relative or true.
24. Trails means tracks displayed by the radar echoes of targets in the form
of a synthetic afterglow. The trails may be either relative or true. The true trails
may be sea or ground stabilized.
25. Echo reference means a facility for indicating that a particular fixed
navigational mark which is being tracked is to be used as a ground stabilized
reference.
26. Trial manoeuvre means a facility to assist the observer in making the
correct manoeuvre for navigation and collision avoidance purposes.
27. Suppressed area means an area set up by the observer within which targets
are not acquired.
28. ERBL means the electronic range and bearing line used to measure bearings
and/or ranges.
29. CPA/TCPA stands for closest point of approach (CPA) and time to closest
point of approach (TCPA) limits from own ship as defined by the observer, to give
warning of when a tracked target or targets will close to within these limits.
30. Bow passing prediction is the situation associated with a target which is
crossing or predicted to cross ahead of own ship.
31. Bad echo is the name associated with a tracked target which appears to
have been temporarily lost or which has a poorly defined radar aspect, so that it
does not have tracking ability.
32. Lost target is the name associated with a target that is no longer being
tracked due to having been lost or obscured.
33. Sea stabilization is a mode of display whereby own ship and all targets
are referenced to the sea, using gyro heading and single axis log water speed
inputs.
34. Ground stabilization is a mode of display whereby own ship and all targets
are referenced to the ground, using ground track or set and drift inputs.
35. Predicted points of collision is a graphical representation of where
predicted collision intercept points lie with respect to own ship and other
targets.
36. PAD means the predicted area of danger defined around a predicted close
quarter situation area. The size is determined by speed ratios between own ship and
the target in question and CPA distance limits as defined by the observer.
37. Map lines means the navigational facility whereby the observer can define
lines to indicate channels or Traffic Separation Schemes. Sometimes called Navlines,
these lines require ground stabilization to stop them drifting.
Note: Where reference is made to target range, bearing, relative course,
relative speed, closest point of approach (CPA) or time to closest point of approach
(TCPA), these measurements are made with respect to the radar antenna.