Abstract

We demonstrate the successful operation of a cw laser Doppler wind sensor at a wavelength of 1.55 µm. At longer ranges (>100 m) the signal conforms closely to complex Gaussian statistics, consistent with the incoherent addition of contributions from a large number of scattering aerosols. As the range is reduced, the probe volume rapidly diminishes and the signal statistics are dramatically modified. At the shortest ranges (<8 m) the signal becomes dominated by short bursts, each originating from a single particle within the measurement volume. These single-particle events can have a very high signal-to-noise ratio (SNR) because (1) the signal becomes concentrated within a small time window and (2) its bandwidth is much reduced compared with multiparticle detection. Examples of wind-signal statistics at different ranges and for a variety of atmospheric backscatter conditions are presented. Results show that single-particle-scattering events play a significant role even to ranges of ∼50 m, leading to results inconsistent with complex Gaussian statistics. The potential is assessed for a low-power laser Doppler wind sensor that exploits the SNR enhancement obtained with single-particle detection.

© 2001 Optical Society of America

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References

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  1. C. Karlsson, F. Olsson, D. Letalick, M. Harris, “All-fiber multifunction continuous-wave 1.55-µm coherent laser radar for range, speed, vibration, and wind measurements,” Appl. Opt. 39, 3716–3726 (2000).
    [CrossRef]
  2. C. M. Sonnenschein, F. A. Horrigan, “Signal-to-noise relationships for coaxial systems that heterodyne backscatter from the atmosphere,” Appl. Opt. 10, 1600–1604 (1971).
    [CrossRef] [PubMed]
  3. R. L. McGann, “Flight test results from a low-power Doppler optical air sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
    [CrossRef]
  4. R. M. Hardesty, R. J. Keeler, M. J. Post, R. A. Richter, “Characteristics of coherent lidar returns from calibration targets and aerosols,” Appl. Opt. 20, 3763–3769 (1981).
    [CrossRef] [PubMed]
  5. M. Harris, G. Constant, C. Ward, “Continuous-wave bistatic laser Doppler wind sensor,” Appl. Opt. (to be published).
  6. P. C. D. Hobbs, “ISICL: In situ coherent lidar for particle detection in semiconductor-processing equipment,” Appl. Opt. 34, 1579–1590 (1995).
    [CrossRef] [PubMed]
  7. M. A. Jarzembski, V. Srivastava, D. M. Chambers, “Lidar calibration technique using laboratory-generated aerosols,” Appl. Opt. 35, 2096–2108 (1996).
    [CrossRef] [PubMed]
  8. F. Durst, A. Melling, J. H. Whitelaw, Principles and Practice of Laser Doppler Anemometry (Academic, London, 1976).
  9. M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226 (1994).
    [CrossRef] [PubMed]
  10. D. G. Brennan, “Linear diversity combining techniques,” Proc. IRE 47, 1075–1102 (1959).
    [CrossRef]
  11. M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
    [CrossRef]

2000

1998

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

1996

1995

1994

1981

1971

1959

D. G. Brennan, “Linear diversity combining techniques,” Proc. IRE 47, 1075–1102 (1959).
[CrossRef]

Brennan, D. G.

D. G. Brennan, “Linear diversity combining techniques,” Proc. IRE 47, 1075–1102 (1959).
[CrossRef]

Chambers, D. M.

Constant, G.

M. Harris, G. Constant, C. Ward, “Continuous-wave bistatic laser Doppler wind sensor,” Appl. Opt. (to be published).

Durst, F.

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

Hardesty, R. M.

Harris, M.

C. Karlsson, F. Olsson, D. Letalick, M. Harris, “All-fiber multifunction continuous-wave 1.55-µm coherent laser radar for range, speed, vibration, and wind measurements,” Appl. Opt. 39, 3716–3726 (2000).
[CrossRef]

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226 (1994).
[CrossRef] [PubMed]

M. Harris, G. Constant, C. Ward, “Continuous-wave bistatic laser Doppler wind sensor,” Appl. Opt. (to be published).

Hill, C. A.

Hobbs, P. C. D.

Horrigan, F. A.

Jarzembski, M. A.

Karlsson, C.

C. Karlsson, F. Olsson, D. Letalick, M. Harris, “All-fiber multifunction continuous-wave 1.55-µm coherent laser radar for range, speed, vibration, and wind measurements,” Appl. Opt. 39, 3716–3726 (2000).
[CrossRef]

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

Keeler, R. J.

Letalick, D.

C. Karlsson, F. Olsson, D. Letalick, M. Harris, “All-fiber multifunction continuous-wave 1.55-µm coherent laser radar for range, speed, vibration, and wind measurements,” Appl. Opt. 39, 3716–3726 (2000).
[CrossRef]

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

McGann, R. L.

R. L. McGann, “Flight test results from a low-power Doppler optical air sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
[CrossRef]

Melling, A.

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

Olsson, F.

Pearson, G. N.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226 (1994).
[CrossRef] [PubMed]

Post, M. J.

Richter, R. A.

Sonnenschein, C. M.

Srivastava, V.

Vaughan, J. M.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

M. Harris, G. N. Pearson, C. A. Hill, J. M. Vaughan, “Higher moments of scattered light fields by heterodyne analysis,” Appl. Opt. 33, 7226 (1994).
[CrossRef] [PubMed]

Ward, C.

M. Harris, G. Constant, C. Ward, “Continuous-wave bistatic laser Doppler wind sensor,” Appl. Opt. (to be published).

Whitelaw, J. H.

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

Appl. Opt.

J. Mod. Opt.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, C. Karlsson, “The role of laser coherence length in continuous-wave coherent lidar,” J. Mod. Opt. 45, 1567–1581 (1998).
[CrossRef]

Proc. IRE

D. G. Brennan, “Linear diversity combining techniques,” Proc. IRE 47, 1075–1102 (1959).
[CrossRef]

Other

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

M. Harris, G. Constant, C. Ward, “Continuous-wave bistatic laser Doppler wind sensor,” Appl. Opt. (to be published).

R. L. McGann, “Flight test results from a low-power Doppler optical air sensor,” in Air Traffic Control Technologies, R. G. Otto, J. Lenz, eds., Proc. SPIE2464, 116–124 (1994).
[CrossRef]

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Figures (3)

Fig. 1
Fig. 1

Time- and frequency-domain (power spectrum) signals for three examples of single particles at ranges of (a) 4, (b) 15, and (c) 50 m. The sampling rate is 50 Msample/s, and the number of samples is 16,384 for R = 4 and 15 m and 8192 for R = 50 m. With a SNR of the order of 40–50 dB, such examples would clearly still be detectable above the noise background at a much reduced laser output power. For the temporal trace at R = 4 m, the width of the Gaussian pulse is determined by the particle transit time. For the trace at R = 50 m, the pulse is not clearly visible in the time domain, but its narrow bandwidth ensures a high SNR in the wind spectrum.

Fig. 2
Fig. 2

Two examples of statistics for the height of the peak spectral bin within the wind-speed spectrum. The atmospheric scattering conditions are quite different, giving rise to large differences in the two data sets. For Set 1 the conditions were warm (∼20 °C), clear (visibility, ∼40 km), and dry for the preceding week, whereas Set 2 was obtained after a night of rain, during which larger particles were likely to have been washed from the atmosphere. The wind speeds were quite light, of the order of 0–5 ms-1. Note the long tails (bearing in mind the logarithmic abscissa) to the distributions at ranges below 50 m. Indeed at the shortest ranges there are occasional large counts [such as that in Fig. 1(a)] that fall well beyond the region plotted.

Fig. 3
Fig. 3

Fit of experimental data to the theory for the largest channel height assuming Gaussian statistics. As expected, the local-oscillator shot noise conforms well to the model. The data at a 250-m range is also well described by Gaussian statistics, but it proves impossible to achieve a satisfactory fit to the data obtained at a short range, owing to the highly non-Gaussian contribution from intermittent high-SNR single-particle events.

Tables (1)

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Table 1 Expected Detection Ratea

Equations (3)

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PSπ/2PTβπλ,
V2λ3R4/π2w4,
PS=CNuexp-Su1-exp-SuN-1,

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