What does range resolution measure in radar systems?

Range resolution in radar systems measures the ability to distinguish between two targets that are close to each other in range or distance. It is essentially a function of the radar's pulse width; a shorter pulse width leads to better range resolution. This is crucial in applications such as air traffic control or military radar, where identifying multiple objects at varying distances is critical. In this context, "narrow" correctly describes the resolution capability, indicating that the radar can effectively differentiate targets that are closely spaced in their range.

The other options do not accurately describe the nature of range resolution. "Leading" refers typically to aspects of timing or priority, "flat" does not relate to any measure of radar performance, and "max range" pertains to the furthest distance the radar can detect targets rather than its resolution capability. Thus, "narrow" is the most appropriate choice to describe the measurement of range resolution in radar systems.