measured by Doppler radars
Doppler radars can measure the component of the velocity of targets
toward or away from the radar. This component is called the "radial
For example, at time T1 a pulse is sent towards a target and it
returns a target distance "D".
2) At time T2, another pulse is sent towards the same
target and returns a target distance
The distance to target has changed from times T1 to T2, resulting in a
phase shift between the two return signals, which
Doppler radars are capable of measuring.
By knowing the phase shift,
the wavelength and the time interval from T1 to T2,
the velocity the target has moved toward or away from the radar can be
If the target is
moving sideways so that its distance relative to the radar does not change,
the radar will record zero radial velocity for that target.