The conventional radar measures the power backscattered by targets which are intercepted by the radar beam. From these measurements the equivalent reflectivity factor and estimates of the rainfall rate can be derived.

In addition to backscattered power, a Doppler radar measures the mean radial velocity and spectral width of radial velocity of targets within the sample volume. These three products are the base data generated by Doppler radars.

Doppler radars measure three base moments: reflectivity, radial velocity and spectrum width.

Doppler radar sends short (~1 ms) pulses of wavelength l followed by a much longer listening period (~1 ms)

In "pulse pair" processing the radial velocity is derived from the phase shift between two successive pulses, NOT the phase shift of one individual pulse due to the target motion (this is an accuracy issue)

Conventional radar locates target in its beam and measures their reflectivity

Radial Velocity

is the component of the velocity that is parallel to the radial from the radar to the point in question

Figure 1. A Doppler radar measures the radial velocity and not the true velocity of the target