Abstract

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.

© 1980 Optical Society of America

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References

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  1. F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser-Doppler Anemometry (Academic, New York, 1976).
  2. T-i. Wang, G. Lerfald, R. S. Lawrence, S. F. Clifford, Appl. Opt. 16, 2236 (1977).
    [CrossRef] [PubMed]
  3. S. Komatsu, A. Watabe, H. Saito, Oyo Butsuri 46, 879 (1977).
  4. T. Abe, O. Sasaki, J. Jpn. Soc. Snow Ice 40, 166 (1978).
    [CrossRef]

1978 (1)

T. Abe, O. Sasaki, J. Jpn. Soc. Snow Ice 40, 166 (1978).
[CrossRef]

1977 (2)

Abe, T.

T. Abe, O. Sasaki, J. Jpn. Soc. Snow Ice 40, 166 (1978).
[CrossRef]

Clifford, S. F.

Durst, F.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser-Doppler Anemometry (Academic, New York, 1976).

Komatsu, S.

S. Komatsu, A. Watabe, H. Saito, Oyo Butsuri 46, 879 (1977).

Lawrence, R. S.

Lerfald, G.

Melling, A.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser-Doppler Anemometry (Academic, New York, 1976).

Saito, H.

S. Komatsu, A. Watabe, H. Saito, Oyo Butsuri 46, 879 (1977).

Sasaki, O.

T. Abe, O. Sasaki, J. Jpn. Soc. Snow Ice 40, 166 (1978).
[CrossRef]

Wang, T-i.

Watabe, A.

S. Komatsu, A. Watabe, H. Saito, Oyo Butsuri 46, 879 (1977).

Whitelaw, J. H.

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser-Doppler Anemometry (Academic, New York, 1976).

Appl. Opt. (1)

J. Jpn. Soc. Snow Ice (1)

T. Abe, O. Sasaki, J. Jpn. Soc. Snow Ice 40, 166 (1978).
[CrossRef]

Oyo Butsuri (1)

S. Komatsu, A. Watabe, H. Saito, Oyo Butsuri 46, 879 (1977).

Other (1)

F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser-Doppler Anemometry (Academic, New York, 1976).

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Figures (8)

Fig. 1
Fig. 1

Arrangement for detection of the Doppler shift frequency.

Fig. 2
Fig. 2

Construction of an LDV that measures selectively a specified velocity vector.

Fig. 3
Fig. 3

Two beams coming out of the two slits.

Fig. 4
Fig. 4

Doppler signals produced in the LDV by the various velocity vectors shown in the lower part of the figure.

Fig. 5
Fig. 5

Block diagram of Doppler signal processing. Operations of each unit are illustrated on the right side.

Fig. 6
Fig. 6

Differences between two velocities measured within a Doppler burst for various velocity vectors.

Fig. 7
Fig. 7

Falling velocity and size of raindrops. The difference between two measured velocities is less than 0.1.

Fig. 8
Fig. 8

Falling velocity and size of raindrops. The difference between two measured velocities is less than 0.03.

Equations (8)

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k i = ( 2 π / λ ) ( 0 , 0 , 1 ) ,
k s = ( 2 π / λ ) ( sin α cos β , sin α sin β , cos α ) ,
f D = 1 2 π ( k s - k i ) · V = 1 λ [ v x sin α cos β + v y sin α sin β + v z ( cos α - 1 ) ] .
sin α sin β = a = const .
- a 2 ξ 2 + ( 1 - a 2 ) η 2 = a 2 d 2 ,
η = a d .
f D = ( 1 / λ ) [ v x ( sin α cos β - sin α cos β ) + 2 a v y + v z ( cos α - cos α ) ] ,
f D = ( 1 / λ ) [ v x ( sin α cos β - sin α cos β ) + v z ( cos α - cos α ) ] .

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