From AMS Glossary
(Abbreviated MTI.) An incoherent Doppler technique for eliminating stationary targets from radar displays.
For each transmitted pulse, the frequency or phase of the returned signal is compared with that of the transmitted signal, and signals are rejected for which there is no change in frequency or phase. MTI was an early technique for detecting airplanes or other moving targets in the presence of clutter. It is not used in modern weather radars.