Abstract

One atmospheric phenomenon that adversely affects laser propagation is optical turbulence. From ten months of observation, the refractive index structure constant in the atmospheric boundary layer was found to be significantly reduced under widespread cloudy conditions. The refractive index structure constant (Cn2 ) depends upon the turbulent flux of momentum, sensible and latent heat. The intensity of a propagating laser beam will not be degraded nearly as much as would be expected under clear or lightly scattered cloud conditions. New experimental data are presented that support this hypothesis. The refractive index structure constant was measured for various cloud-cover conditions.

© 2006 Optical Society of America

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References

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  1. L.C. Andrews and R.L. Phillips, "Laser Beam Propagation through Random Media," (SPIE Optical Engineering Press, Bellingham, WA, 1998).
  2. Installation Guide. LOA-004-xR Long Baseline Optical Anemometer and Atmospheric Turbulence Sensor. Revision 5/5/98. Scientific Technology, Inc., Gaithersburg, MD, (1998).
  3. R.S. Lawrence, G.R. Ochs, and S.F. Clifford, "Use of scintillations to measure average wind across a light beam," Appl. Opt. 11, 239-243, (1972).
    [CrossRef] [PubMed]
  4. D.L. Hutt, "Modeling and measurements of atmospheric optical turbulence over land," Opt. Eng. 38, 1288-1295, (1999).
    [CrossRef]
  5. E. Ryznar, J. Bartlo, "Dependence of Cn2(Ct2) in the atmospheric boundary layer on conventional meteorological variables," The University of Michigan, College of Engineering, Department of Atmospheric & Oceanic Science, Ann Arbor, MI 48109-2143, AFGL-TR-86-0013, Final report 15 September 1983 - 14 December (1985).
  6. R.E. Bird, R. L. Hulstrom, A simplified clear sky model for direct and diffuse insolation on horizontal surfaces, Report SERI/TR-642-761, DOE Contract No. EG-77-C-01-4042, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, Colorado, February (1981).
  7. A. Chehbouni, O. Hartogensis, Y. Kerr, L. Hipps, J. Brunel, I. Watts, J. Rodrigues, G. Boulet, G. Dediew, and H. De Bruin, "Sensible heat flux measurements using a large aperture scintillometer over heterogeneous surface," American meteorological society, special symposium on hydrology, Phoenix, Arizona, 11-16 Jan, (1998).
  8. A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.
  9. A. Chehbouni, C. Watts, Y. Kerr, G. Dediew, J. Rodrigues, F. Santiago, P. Cayrol, G. Boulet, D. Goodrich, "Methods to aggregate turbulent flux over heterogenous surfaces," application to SALSA data in Mexico, data set in Mexico, Agriculture meteorol, SALSA, research, 1999.
  10. F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)
  11. D. L. Walters, Kunkel, "Atmospheric modulation transfer function for desert and mountain locations: the atmospheric effects on ro," journal of the optical Society of America, Vol 71, 397-405, (1981)
  12. Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
    [CrossRef]

2004

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

1999

D.L. Hutt, "Modeling and measurements of atmospheric optical turbulence over land," Opt. Eng. 38, 1288-1295, (1999).
[CrossRef]

1985

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

1972

Beland, R.

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

Bonnefond, J.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Chehbouni, A.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Clifford, S.F.

Dediew, G.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Dewan, F.

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

Doss-Hammel, S.

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

Eaton, F. D.

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

Garvy, D. M.

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

Goodrich, D. C.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Hutt, D.L.

D.L. Hutt, "Modeling and measurements of atmospheric optical turbulence over land," Opt. Eng. 38, 1288-1295, (1999).
[CrossRef]

Kerr, Y.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Lagouarde, J.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Lawrence, R.S.

Ochs, G.R.

Oh, E.

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

Oh, Y. H.

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

Ricklin, J. C.

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

Rodrigues, J.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Santiago, F.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Unkrich, C.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Watts, C.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Appl. Opt.

Opt. Eng.

D.L. Hutt, "Modeling and measurements of atmospheric optical turbulence over land," Opt. Eng. 38, 1288-1295, (1999).
[CrossRef]

Proc. SPIE

F. D. Eaton, D. M. Garvy, F. Dewan, R. Beland, "Transverse coherence length (ro) observations", Proc. SPIE, Vol  551, 42-50(1985)

Y. H. Oh,J. C. Ricklin, E. Oh, S. Doss-Hammel, F. D. Eaton, "Estimating optical turbulence effects on free-space laser communication: modeling and measurements at ARL’s A_LOT facility," Proc. SPIE Vol.  5550, p. 247-255, (2004)
[CrossRef]

Water Resour. Res.

A. Chehbouni, C. Watts, J. Lagouarde, Y. Kerr, J. Rodrigues, J. Bonnefond, F. Santiago, G. Dediew, D. C. Goodrich and C. Unkrich, "Estimation of Heat and momentum fluxes over complex terrain using a large aperture scintillometer," Water Resour. Res. 35(8), 2505.

Other

A. Chehbouni, C. Watts, Y. Kerr, G. Dediew, J. Rodrigues, F. Santiago, P. Cayrol, G. Boulet, D. Goodrich, "Methods to aggregate turbulent flux over heterogenous surfaces," application to SALSA data in Mexico, data set in Mexico, Agriculture meteorol, SALSA, research, 1999.

L.C. Andrews and R.L. Phillips, "Laser Beam Propagation through Random Media," (SPIE Optical Engineering Press, Bellingham, WA, 1998).

Installation Guide. LOA-004-xR Long Baseline Optical Anemometer and Atmospheric Turbulence Sensor. Revision 5/5/98. Scientific Technology, Inc., Gaithersburg, MD, (1998).

E. Ryznar, J. Bartlo, "Dependence of Cn2(Ct2) in the atmospheric boundary layer on conventional meteorological variables," The University of Michigan, College of Engineering, Department of Atmospheric & Oceanic Science, Ann Arbor, MI 48109-2143, AFGL-TR-86-0013, Final report 15 September 1983 - 14 December (1985).

R.E. Bird, R. L. Hulstrom, A simplified clear sky model for direct and diffuse insolation on horizontal surfaces, Report SERI/TR-642-761, DOE Contract No. EG-77-C-01-4042, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, Colorado, February (1981).

A. Chehbouni, O. Hartogensis, Y. Kerr, L. Hipps, J. Brunel, I. Watts, J. Rodrigues, G. Boulet, G. Dediew, and H. De Bruin, "Sensible heat flux measurements using a large aperture scintillometer over heterogeneous surface," American meteorological society, special symposium on hydrology, Phoenix, Arizona, 11-16 Jan, (1998).

D. L. Walters, Kunkel, "Atmospheric modulation transfer function for desert and mountain locations: the atmospheric effects on ro," journal of the optical Society of America, Vol 71, 397-405, (1981)

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Figures (16)

Fig. 1.
Fig. 1.

Scattering of light rays in turbulent air near hot ground (negative temperature gradient).

Fig. 2.
Fig. 2.

Build-up of a negative temperature gradient when the Sun heats the Earth (a) and elimination of the gradient when the sunlight is blocked by a cloud (b).

Fig. 3.
Fig. 3.

Schematic of the experimental scintillometer for the measurement of the refractive index structure constant.2 It consists of three major units: transmitter 1, receiver 2, and signal processing unit 3. Transmitter 1 includes LED 4, mirror 5, and LED modulator 6. Light emitted by LED 4 propagates through turbulent air 7 along two paths 8 and 9. The receiver consists of two identical sub-units. Each of them has mirrors 10 and 11, photodetectors 12 and 13, detector control units 14 and 15. Signals 16 and 17 from the receiver sub-units enter the processing unit 3. Signal processing unit 3 consists of two identical channels made of preamplifiers 18 and 19 and demodulators 20 and 21. Signals from demodulators 20 and 21 enter Cn2 processor 22 and covariance processor 23. Cn2 data is stored in unit 24, and covariance. The refractive index structure constant can be obtained from equation[2] data is stored in unit 25. Both sets of data are sent to digital processor 26, which sends the data to a computer.

Fig. 4.
Fig. 4.

(A) Cn2 and (B) solar irradiance for May 11, 2004. Each data point was obtained by averaging over a 15 minute interval.

Fig. 5.
Fig. 5.

(A) Crosswind, (B) solar irradiance, and (C) Cn2 for (a) June 21, (b) July 7, and (c) July 12, 2004. Data was taken in ten second intervals. cloud cover as varied from10% to 90% based on estimations by observer.

Fig. 6.
Fig. 6.

Log [Cn2 ] plotted versus log [Solar irradiance] for (a) June 21, (b) July 7, and (c), (d) July 12 2004. The plots are obtained from raw data presented in Fig. 3. Data points in plot (d) correspond to time between 11:35 am and 12:00 pm when there was a continuous cloud-cover with variable density. Pearson’s factor r of correlation between log [Cn2 ] and log [Solar irradiance] is 0.75 for plot (b) 0.74 for plot (c), and 0.93 for plot (d). Cloud cover was between 10% and 90% based on the estimations of the observer.

Fig. 7.
Fig. 7.

Log [Cn2 ] plotted versus the speed of the crosswind for July 12 2004. The plot is obtained from raw data presented in Fig. 3. Correlation factor is 0.105.

Fig. 8.
Fig. 8.

Log [Cn2 ] plotted versus the peak wind speed for July 12 2004. The data points were taken at a rate of one point per every 15 min.

Fig. 9.
Fig. 9.

Log [Cn2 ] plotted versus the relative humidity for July 12 2004. The data points were taken at a rate of one point per every 15 min.

Fig. 10.
Fig. 10.

Log [Cn2 ] plotted versus the static atmospheric pressure for July 12 2004. The data points were taken at a rate of one point per every 15 min.

Fig. 11.
Fig. 11.

Log [Cn2 ] plotted versus the direction of the wind for July 12 2004. The data points were taken at a rate of one point per every 15 min.

Fig. 12.
Fig. 12.

Log [Cn2 ] plotted versus the temperature for 7 July 2004. The data points were taken at a rate of one point per every 15 min. Correlation factor is 0.62.

Fig. 13.
Fig. 13.

Log [Cn2 ] plotted versus the temperature difference for 7 July 2004. The data points were taken at a rate of one point per every 15 min. Correlation factor is -0.59.

Fig. 14.
Fig. 14.

Log [Cn2 ] plotted versus log [Solar irradiance] for 28 June 2004. The data points were taken at a rate of one point per every 15 min. There was rain and overcast through the day. Correlation factor is 0.95.

Fig. 15.
Fig. 15.

Log [Cn2 ] plotted versus log [Solar irradiance] for May 11, 2004 for the whole day (as shown in Fig. 4).

Fig. 16.
Fig. 16.

The drop of Log [Cn2 ] versus the drop of log [Solar irradiance] for May 11, 2004 for the whole day.

Tables (1)

Tables Icon

Table 1. Cumulative data on the Pearsons correlation coefficients between the structure constant and the irradiance and between the structure constant and the crosswind speed for the midday during ten months of observation

Equations (4)

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C n 2 = [ n ( r 1 ) n ( r 2 ) ] 2 r 1 r 2 2 3 ,
C n 2 2 k 7 6 d 11 6 σ I 2 ,
σ I 2 = I 2 I 2 1 ,
B I ( τ ) = 8 π 2 k 2 d 0 1 0 k Φ n ( κ ) J 0 ( κ V c τ ) { 1 cos [ κ 2 d k ξ ( 1 ξ ) ] } d κ d ξ ,

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