Which pair of measurements are used to assess collision risk on radar?

• A. Bearing and distance
• B. Range and bearing
• C. Speed and direction
• D. Color and brightness

Answer: (B)

The main idea is that radar-based collision risk relies on knowing where another vessel is relative to you. That comes from the target’s range and bearing. Range tells you how far away the target is, and bearing tells you the direction to the target from your ship. With both, you can plot the target’s position on your radar screen and evaluate how it will move relative to you, allowing you to judge closest-point-of-approach and decide on any needed action.

Speed and direction describe how the target is moving, which helps predict future positions, but they don’t give your current relative location by themselves. Color and brightness don’t provide distance or direction information. In radar practice, the standard way to express the two key measurements is range and bearing.