When a vessel follows the circular path of a turn, fixed targets displayed on a radar in the head up orientation will follow a predictable track concentric to the turn’s centre. (see figure 1).
Figure 1 – Concentric movement of fixed targets on a head up display during a turn
Notable features of the head up orientation during a turn are:
- A target at the turn centre will remain stationary.
- All other fixed targets will follow a circular path around the turn centre.
- The amount of movement of a target is proportional to its distance from the turn centre.
The characteristics of head up orientation during a turn may be used for planning, executing and monitoring turns. This particularly applies to radars that allow the variable range marker (VRM) ring to be offset. Many radars have this ability coupled with an unstabilised display and the presentation of target wakes or trails.