What shape is formed when LOBs cross, and how is it used in the LKP scenario?

• A. A circle; used for target centering
• B. A rectangle; used to grid the search
• C. An ellipse; used to drift in the LKP scenario
• D. A straight line indicating a single track

Answer: (C)

When you’re dealing with lines of bearing and drift in a Last Known Point scenario, the area where the target could be located isn’t a precise point. The crossing of lines of bearing gives you the best estimate, but measurement errors and, crucially, the target’s drift after the last known point create a spread in possible positions. Representing that spread as an ellipse is standard because it captures directional uncertainty: you’re more uncertain along the dominant drift direction (long axis) and less uncertain perpendicular to it (short axis).

The ellipse is centered on the last known point and oriented to align with the prevailing drift. Its axes lengths reflect how much the wind/current could push the subject in those directions, and over time the ellipse grows as uncertainty accumulates. This shape directly informs search planning: you design patterns to cover the ellipse so you maximize the chance of detection, updating the ellipse as new data comes in.

Why not other shapes? A circle would imply equal uncertainty in all directions, which isn’t realistic when drift has a preferred direction. A rectangle would imply a grid-based boundary rather than a probabilistic spread. A straight line would suggest a single track with no uncertainty, which isn’t how drift and measurement error work.