A new laser Doppler velocimeter (LDV) where the waveform of Doppler signal changes according to the direction of the velocity vector is proposed. This feature makes it possible to measure selectively a specified velocity vector. A practical LDV system is constructed to be applied to the measurement of the falling velocity of raindrops. In this system the selection of a specified velocity vector is carried out by the detection of a difference between the two periods separated by one cycle of Doppler frequency in a Doppler burst. The experimental results show clearly the usefulness of this system.
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