What does the cosine effect refer to in the context of radar and lidar?

The cosine effect in the context of radar and lidar involves the principles of geometry when measuring the speed of an object. It relates specifically to how the angle between the radar or lidar beam and the direction of the target's movement affects the calculated speed of the target. As the angle increases, the effective component of the target's speed that is detected decreases due to the cosine of that angle.

When the radar or lidar is aligned directly in line with the direction of the target, the velocity measurement is accurate. However, if the target is moving at an angle across the beam (not directly toward or away), the measured speed will be less than the actual speed, which can lead to underreporting or miscalculating the vehicle's speed. Thus, understanding the cosine effect is crucial for accurately interpreting speed readings in real-world scenarios.

Other concepts mentioned, such as the speed itself, clearing distances, or variances in calculations, do not capture the essential geometric basis of the cosine effect, which is fundamentally about how angle influences the accuracy of speed measurements in radar and lidar systems.