Basic on E-Nav 2

Topics: Navigation, Angular momentum, Radar Pages: 5 (1020 words) Published: September 14, 2013
basic on electronic navigation 2

APPENDIX

Definitions of terms to be used in connection with ARPA performance standards

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 or 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.

* Refer to IEC 872: Marine Automatic Radar Plotting AIDS (ARPAs)

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.

6. True Speed means the speed of a target obtained by a vector combination of target relative motion and own ship’s true motion

7. True Motion means the combination of true course and true speed.

8. True Bearing means the direction of a target from own ship 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 Stabilised Display means a display in which the azimuth orientation relative to a nominated true bearing is fixed.

13. North-Up Display means an azimuth-stabilised display in which a line connecting the centre with the top of the display is north true motion.

14. Course-Up Display means an azimuth stabilised 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 Swoop 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 arena set up by the observer which should automatically acquire a target when it enters such an area

23. History means equally time-space 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 grounded stabilised.

Each Reference means a facility for indicating that a particular fixed navigational mark, which is being tracked, is to be used as a ground stabilised reference.

* For the purpose of these definitions there is need to distinguish between sea and ground stabilisation

26. Trail Manoeuvre means a facility to assist the...
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