What does the 'cosine effect' refer to in speed detection?

The 'cosine effect' in speed detection primarily refers to how the angle of the radar or lidar beam in relation to the direction of the vehicle influences the accuracy of speed measurements. When the radar beam is not aligned directly with the vehicle's path, the speed detected may be less than the actual speed of the vehicle. This phenomenon occurs because the radar measures the speed component that is in line with the beam, which is reduced when the vehicle approaches at an angle.

For example, if a vehicle is moving perpendicular to the radar beam, the measured speed could be significantly lower than the actual speed, leading to inaccuracies in speeding citations. Conversely, if the vehicle is approaching directly towards the radar device, the measured speed will be closer to the actual speed. Understanding the cosine effect is essential for law enforcement officers using radar or lidar for speed detection, as it allows for more accurate assessments and helps avoid erroneous interpretations of the data collected.