Which measurement does fire control radar primarily use to differentiate between targets?

Fire control radar primarily uses frequency and signal strength as the key measurements to differentiate between targets. The radar emits electromagnetic signals and the targets reflect these signals back. The frequency of the received signals can indicate the relative motion of the target due to the Doppler effect, where the frequency changes based on whether the target is moving toward or away from the radar.

Signal strength also plays a fundamental role in determining how distinguishable a target is, as different materials and shapes can reflect radar signals with varying degrees of intensity. By analyzing the frequency variations and the strength of the returned signals, fire control systems can effectively identify and classify targets based on their behaviors and physical characteristics.

The other options do not capture the primary operational principles of fire control radar. For instance, distance and speed are important parameters, but they are derived from the fundamental measurements of frequency and time. Size and temperature, as well as color and shape, are more relevant to visual observation techniques and are not primary metrics employed by radar systems. Consequently, focusing on frequency and signal strength provides a clearer understanding of how fire control radar operates in differentiating between various targets.