Abstract

We extend the functionality of a low-cost CW diode laser coherent lidar from radial wind speed (scalar) sensing to wind velocity (vector) measurements. Both speed and horizontal direction of the wind at ~80 m remote distance are derived from two successive radial speed estimates by alternately steering the lidar probe beam in two different lines-of-sight (LOS) with a 60° angular separation. Dual-LOS beam-steering is implemented optically with no moving parts by means of a controllable liquid-crystal retarder (LCR). The LCR switches the polarization between two orthogonal linear states of the lidar beam so it either transmits through or reflects off a polarization splitter. The room-temperature switching time between the two LOS is measured to be in the order of 100 μs in one switch direction but 16 ms in the opposite transition. Radial wind speed measurement (at 33 Hz rate) while the lidar beam is repeatedly steered from one LOS to the other every half a second is experimentally demonstrated – resulting in 1 Hz rate estimates of wind velocity magnitude and direction at better than 0.1 m/s and 1° resolution, respectively.

© 2014 Optical Society of America

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References

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  1. R. S. Hansen and C. Pedersen, “All semiconductor laser Doppler anemometer at 1.55 µm,” Opt. Express 16(22), 18288–18295 (2008).
    [Crossref] [PubMed]
  2. P. J. Rodrigo and C. Pedersen, “Doppler wind lidar using a MOPA semiconductor laser at stable single-frequency operation,” in Technical Digest. 19th International Congress on Photonics in Europe, CLEO/Europe-EQEC (2009).
    [Crossref]
  3. P. J. Rodrigo and C. Pedersen, “Field performance of an all-semiconductor laser coherent Doppler lidar,” Opt. Lett. 37(12), 2277–2279 (2012).
    [Crossref] [PubMed]
  4. P. J. M. Clive, “Lidar and resource assessment for wind power applications: the state of the art,” Proc. SPIE 7111, 711107 (2008).
    [Crossref]
  5. M. Harris, M. Hand, and A. Wright, “Lidar for turbine control,” Technical Report NREL/TP-500–39154, NREL, January 2006.
  6. E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
    [Crossref]
  7. M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
    [Crossref]
  8. Q. Hu, P. J. Rodrigo, and C. Pedersen, “Remote wind sensing with a CW diode laser lidar beyond the coherence regime,” Opt. Lett. 39(16), 4875–4878 (2014).
    [Crossref] [PubMed]

2014 (2)

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Q. Hu, P. J. Rodrigo, and C. Pedersen, “Remote wind sensing with a CW diode laser lidar beyond the coherence regime,” Opt. Lett. 39(16), 4875–4878 (2014).
[Crossref] [PubMed]

2012 (1)

2008 (2)

P. J. M. Clive, “Lidar and resource assessment for wind power applications: the state of the art,” Proc. SPIE 7111, 711107 (2008).
[Crossref]

R. S. Hansen and C. Pedersen, “All semiconductor laser Doppler anemometer at 1.55 µm,” Opt. Express 16(22), 18288–18295 (2008).
[Crossref] [PubMed]

1998 (1)

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

Churchfield, M.

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Clive, P. J. M.

P. J. M. Clive, “Lidar and resource assessment for wind power applications: the state of the art,” Proc. SPIE 7111, 711107 (2008).
[Crossref]

Gebraad, P.

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Hansen, R. S.

Harris, M.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

Hu, Q.

Karlsson, C. J.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

Letalick, D.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

Pao, L. Y.

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Pearson, G. N.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

Pedersen, C.

Rodrigo, P. J.

Simley, E.

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Vaughan, J. M.

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

J. Mod. Opt. (1)

M. Harris, G. N. Pearson, J. M. Vaughan, D. Letalick, and C. J. Karlsson, “The role of laser coherence length in continuous-wave coherent laser radar,” J. Mod. Opt. 45(8), 1567–1581 (1998).
[Crossref]

J. Phys. Conf. Ser. (1)

E. Simley, L. Y. Pao, P. Gebraad, and M. Churchfield, “Investigation of the impact of the upstream induction zone on LIDAR measurement accuracy for wind turbine control applications using large-eddy simulation,” J. Phys. Conf. Ser. 524, 012003 (2014).
[Crossref]

Opt. Express (1)

Opt. Lett. (2)

Proc. SPIE (1)

P. J. M. Clive, “Lidar and resource assessment for wind power applications: the state of the art,” Proc. SPIE 7111, 711107 (2008).
[Crossref]

Other (2)

M. Harris, M. Hand, and A. Wright, “Lidar for turbine control,” Technical Report NREL/TP-500–39154, NREL, January 2006.

P. J. Rodrigo and C. Pedersen, “Doppler wind lidar using a MOPA semiconductor laser at stable single-frequency operation,” in Technical Digest. 19th International Congress on Photonics in Europe, CLEO/Europe-EQEC (2009).
[Crossref]

Supplementary Material (1)

» Media 1: AVI (1133 KB)     

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Figures (5)

Fig. 1
Fig. 1

The WindEye – a dual-LOS wind lidar. It makes use of an optical circulator/switch (OCS) to non-mechanically steer the transmitted laser beam to either LOS1 or LOS2 and to direct the received backscatter to the photodetector (PD). A field-programmable gate array (FPGA) unit calculates the lidar signal power spectra. The laser, controllers, power supply unit (PSU) and FPGA-based data processor are linked to the two-eyed optical transceiver by 10 m long fiber and electrical cables. The inset shows a sketch of the WindEye mounted on a turbine.

Fig. 2
Fig. 2

Non-mechanical beam-steering system with a liquid-crystal retarder (LCR). The LCR with a 10 mm clear aperture is electronically addressed to either preserve the input beam polarization state (p-polarized for high LCR drive voltage) or change it to its orthogonal counterpart (s-polarized for low drive voltage). p-polarized (/s-polarized) beam is transmitted through (/reflected off) the polarization beam splitter and deflected by a mirror to send the beam along LOS1 (/LOS2). Both LOS1 (green dashed line) and LOS2 (red dashed line) make an angle α=30° with the lidar axis (black dashed line). A blue arrow illustrates a possible orientation of the wind velocity vector v with an azimuthal direction ϕ relative to the lidar axis (ϕ is positive for this particular example).

Fig. 3
Fig. 3

(Top) Measured relative power of the laser beam versus time, alternately transmitted along LOS1 (green) and LOS2 (red), along with the corresponding LCR drive voltage (gray) that enables this non-mechanical lidar beam-steering mechanism. (Bottom) Time constants for switching the beam from LOS1 to LOS2 and vice versa (i.e. τ12 and τ21) are estimated by fitting exponential decay curves to the relative beam power transitions at 0.5 s and 0.0 s, respectively. The measurements were performed at an ambient temperature of 25 °C.

Fig. 4
Fig. 4

Power spectral density (PSD) of the lidar photodetector output signal when LOS1 is active (top) and when the lidar switches to LOS2 (bottom). PSD plots are given in units of the shot noise background. For each LOS, the radial wind speed is directly proportional to the estimated center frequency of the Doppler peak (e.g. 5 MHz for LOS1 and 3 MHz for LOS2 for the above plots). The time stamp of each plot is shown on their upper right corner. An accompanying video clip (Media 1) is included to show the 33 Hz lidar spectra for a period of 10 s while the beam switches from one LOS to another every half a second. Assuming laminar flow, equal radial wind speeds are obtained when the wind vector is parallel to the lidar axis (or symmetry axis between LOS1 and LOS2).

Fig. 5
Fig. 5

Plots of the 1 Hz radial wind speed data for LOS1 and LOS2 (top) and the corresponding estimates for the magnitude and direction (measured relative the lidar axis) of the wind velocity vector. Time axis is in units of hours:minutes.

Equations (3)

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v LOS = λ 2 f D .
| v |cosϕ= ( v LOS1 + v LOS2 ) 2cosα ,
| v |sinϕ= ( v LOS2 v LOS1 ) 2sinα .

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