What aspect does Specific Differential Phase (KDP) primarily measure?

Specific Differential Phase, often abbreviated as KDP, is a measurement that represents the spatial rate of change of the differential phase shift between horizontally and vertically polarized radar waves as they propagate through a medium, typically precipitation. The differential phase shift itself is the difference in the phase of the returned signals from horizontally and vertically polarized waves.

When we speak of KDP as the derivative of the differential phase shift with respect to range, we are emphasizing the change in this phase shift over a distance. This is crucial because KDP provides valuable information about the size and shape of the rain drops or other particles present in the radar's beam. It enables meteorologists to distinguish between different types of precipitation, such as light rain, heavy rain, or hail.

The other aspects mentioned, such as the impact of phase shift on radar range, the frequency of the radar signal, or the reflectivity of precipitation, do not capture the essence of what KDP measures. KDP is specifically concerned with how the differential phase evolves as the radar signal travels through a medium, making option B the precise definition of what KDP represents in radar meteorology.