Which of the following best defines the term 'signal speed' in this context?

The term 'signal speed' refers to the rate at which a signal travels through a medium, which is best defined as the distance covered over a period of time. In the context of RADAR and LIDAR, this speed is crucial for determining how quickly data about targets is collected and analyzed.

When signals, whether they be radio waves in RADAR or light waves in LIDAR, propagate through space or any other medium, their speed can significantly affect the time it takes for a signal to return after bouncing off an object. This travel time is essential for calculating distances and other related measurements, making it fundamentally linked to the concept of distance per unit time.

Strength of the signal received, change in amplitude, and frequency of pulse emissions relate to other characteristics of signals or waveforms but do not directly describe how fast the signal is transmitted or travels through its medium. Thus, defining 'signal speed' as the distance covered over a period of time accurately captures its essence in both RADAR and LIDAR systems.