When is something considered a 'lost target'?

• A. When 5/10 consecutive sweeps do not sense a target
• B. When a target disappears from the radar
• C. When the AIS malfunctions
• D. When the vessel changes course

Answer: (A)

A lost target is identified by a sustained lapse in detection over a defined number of consecutive radar scans. The idea is not to treat a single miss as loss, but to require several misses before the track is considered gone. In practice, a threshold like five out of ten consecutive sweeps failing to sense the target is used, so if detections are missing in that window, the system marks the target as lost and stops updating its position. This prevents temporary clutter, shadowing, or momentary signal issues from causing a false active track.

Disappearance from the radar in a single sweep isn’t enough to label a target lost, because it could reappear in the next scan. An AIS malfunction is a separate issue tied to identity and data integrity, not the radar tracking state. A vessel changing course can affect where a target appears, but it doesn’t in itself define a lost target.