What does a lower frequency reflected signal indicate in the context of relative motion?

In the context of radar and lidar, the frequency of the reflected signal is directly related to the relative motion between the radar or lidar sensor and the object being measured. When an object is moving away from the sensor, the frequency of the reflected signal is lower due to the Doppler effect. This phenomenon occurs because as the object moves away, it causes the waves to stretch, resulting in a lower frequency (or longer wavelength) of the signal that is detected upon reflection.

This lower frequency indicates that there is a relative motion where the distance between the sensor and the object is increasing. Therefore, if a lower frequency reflected signal is detected, it signifies that the object is moving away from the radar or lidar system, aiding in the determination of the object's trajectory or movement pattern in relation to the sensor.

Higher frequency signals, on the other hand, would indicate that the object is moving closer to the sensor, while situations involving jamming would not typically result in a consistent and interpretable shift in frequency.