User's Manual

RADARPILOT / CHARTRADAR
ED 3038 G 232 / 01 (2002-06)
Operating Instructions
7 ARPA Functions
7.2 Procedure of the Target Acquisition
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7.2 Procedure of the Target Acquisition
The ARPA radar permits manual and automatic acquisition of up to 50 targets. For automatic target
acquisition, there are two combined acquisition and surveillance zones
1)
available. Acquired targets are
tracked automatically.
In the case of manual target acquisition, the target video is marked manually, and is thus initially
provided with the dotted square . The radar then checks during the next three revolutions of the
antenna to determine whether the echo occurs twice at this position. If it does, this target is tracked auto-
matically by the radar. If it does not, the radar does not recognise any target at this position, and the
LOST TGT alarm occurs. The target just acquired but lost is marked with the flashing symbol .
In the case of automatic target acquisition, the radar evaluates all radar echoes appearing in the acqui-
sition/guard zones. If the echo appears at a certain position at least six times during ten revolutions of
the antenna, it is evaluated as a radar target.
If the echoes do not belong to a target already being tracked, the position is treated as an acquired target
and is marked with the flashing symbol . The alarm TARGET IN AZ appears, or - if the target was
already being tracked when it entered the acquisition/guard zone - the alarm TARGET IN GZ appears.
After acknowledgement of the alarm, the automatic target tracking begins.
☞ Automatic target acquisition is switched on and off together with the display of the acquisition/guard
zone - see page 69.
☞ If there are already 50 targets being tracked and another target is then acquired, the AZ OVER-
FLOW alarm appears. In this case, at least one non-critical target must first be deleted.
When the automatic tracking begins, the radar determines the movement of the target.
- If the absolute speed determined for the target is less than 1.5
κν, the target is classed as a fixed
target; the symbol appears.
- If the speed of the target exceeds 1.5 kt, it is classed as a moving target and is marked with the
symbol .
- If the functions are switched on, also the speed vector is now displayed, the computation of collision
risks is performed continuously, and the past position plot is built up.
The target is now tracked automatically until
- it is deleted manually or
- it is lost because, during five revolutions of the antenna, no correlation of the video can be found by
the radar, or the detection probability falls below 50%, or
- it leaves the target tracking range of 20 NM.
If a target is lost, a LOST TGT alarm appears and the lost target is marked accordingly.
☞ The number of targets being tracked should be kept as small as possible; the presence of too many
targets causes confusion on the screen and distracts the operator’s attention from what is really
important.
Targets that are no longer relevant should be deleted in order to minimise the number of LOST TGT
alarms caused by targets leaving the radar range.
☞ In the case of tracked targets entering a clutter area (rain or sea clutter), a "target swap" might occur;
parts of the rain front are suddenly being "tracked". A target swap can also occur if there are targets
situated close together or close to land. In the case of target swaps, no warning is given.
WARNING:
Automatic target acquisition and tracking are ensured only if the radar
video is OK, i.e. if it is adjusted in the same way as would also be neces-
sary for visual evaluation.
1)
Called acquisition/guard zone in the following