Specific Differential Phase - KDP
KDP is the range derivative of φDP
(°/km). The difference in phase per kilometer of received horizontally
and vertically polarized waves is almost linearly related to rain rate.
It requires the integration of a large range (e.g. 5 km) to get a
meaningful estimate. KDP varies with D3, not D6, and is independent of the radar calibration and is not subject to attenuation.