Abstract

Diffractive target plates are used to emulate aerosols of known size and concentration. These target plates are used to validate and determine the sensitivity of a multiple-field-of-view lidar signal inversion technique based on double-scattering measurement to retrieve the particle size and the concentration of small optical depth clouds. We estimate that nighttime and daytime quantification (size and concentration) is possible for optical depths as low as 0.005 and 0.016, respectively. The recovery technique limiting factors are the shot noise, the laser features, the optical lens quality, the background illumination level, the background aerosol fluctuations, and the noise introduced by the lidar detector, a gated intensified camera (camera G-ICCD).

© 2008 Optical Society of America

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References

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  1. G. Roy and N. Roy, “Standoff determination of the particle size and concentration of small optical depth clouds based on double scattering measurements: concept and experimental validation with bioaerosols,” Appl. Opt. 47, 1336-1349 (2008).
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  3. J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.
  4. L. Katsev, E. P. Zege, A. S. Prikhach, and I. N. Polonsky, “Efficient technique to determine backscattered light power for various atmospheric and oceanic sounding and imaging systems,” J. Opt. Soc. Am. A 14, 1338-1346 (1997).
    [CrossRef]
  5. N. Roy, G. Roy, L. R. Bissonnette, and J.-R. Simard, “Measurement of the azimuthal dependence of cross-polarized lidar returns and its relation to optical depth,” Appl. Opt. 43, 2777-2785 (2004).
    [CrossRef] [PubMed]
  6. A User's Guide to the: Andor iStar, version V3 (Andor Technology, 2001).
  7. G. Roy, L. R. Bissonnette, C. Bastille, and G. Vallée, “Retrieval of droplet-size density distribution from multiple field-of-view cross-polarized lidar signals,” Appl. Opt. 38, 5202-5211(1999).
    [CrossRef]

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Abbot, D.

J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.

Bastille, C.

Beer, J. M.

J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.

Bissonnette, L. R.

Katsev, L.

McCreath, G. C.

J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.

Polonsky, I. N.

Prikhach, A. S.

Roy, G.

Roy, N.

Simard, J.-R.

Swithenbank, J.

J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.

Taylor, D. S.

J. Swithenbank, J. M. Beer, D. S. Taylor, D. Abbot, and G. C. McCreath, “A laser diagnostic technique for the measurement of droplet and particle size distribution,” in 14th American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting (American Institute of Aeronautics and Astronautics, 1976), pp. 76-69.

Vallée, G.

Zege, E. P.

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Figures (11)

Fig. 1
Fig. 1

Experimental setup showing the geometry of the measurement and various scattering considered in the presence of a cloud and in the presence of its emulation with a diffractive target plate.

Fig. 2
Fig. 2

Data acquisition and treatment scheme.

Fig. 3
Fig. 3

(a) Normalized lidar return on background aerosols obtained in the presence of diffractive target with etched particles; (b) the same measurement in the presence of the reference target; (c) is (a) minus (b). (d) Image analysis in terms of encircled energy in logarithmic spaced rings delimited by θ i and θ i + 1 .

Fig. 4
Fig. 4

Comparison of a nighttime measurement for two different camera gate widths (20 and 60 ns ) and sounding distances ( z c = 155 m and z c = 175 m ) for particle diameters of 20 and 50 μm .

Fig. 5
Fig. 5

Comparison of a nighttime and daytime measurement for a camera gate width of 60 ns , z c = 175 m , and etched-particle diameter 50 μm .

Fig. 6
Fig. 6

Representation of a photointensification event.

Fig. 7
Fig. 7

Comparison of Δ P norm ( θ i + 1 θ i ) standard deviation of the data with the error associated with the G-ICCD camera and the standard deviation of the number of detected photons according to Poisson statistics.

Fig. 8
Fig. 8

Comparison of Δ P norm ( θ i + 1 θ i ) curve and standard deviation for a single measurement and the summing of 25 acquisitions.

Fig. 9
Fig. 9

Measurement of the background light subtraction acquisition method’s efficiency.

Fig. 10
Fig. 10

Effect of background light subtraction acquisition. (a) Camera gate width 20 ns , z c = 175 m , and 50 μm diameter etched-particles target; (b) same as (a) with a camera gate width of 60 ns ; (c) same as (b) for the reference target.

Fig. 11
Fig. 11

Comparison of Δ P Norm ( θ i + 1 θ i ) theoretical profile for linear and logarithmic spaced rings for 20 and 50 μm diameter etched particles when z a = 123 m and z c = 155.5 m .

Tables (6)

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Table 1 Diameters, Densities N p , and Total Number N of Etched Particles on Fused Silica Plates

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Table 2 Size Retrieval and Its Associated Error, Target at 123 m , Gate Width 20 ns a

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Table 3 Size Retrieval and Its Associated Error, Target at 123 m , Gate Width 60 ns a

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Table 4 Optical Depth Retrieval and Its Associated Error, Target at 123 m , Gate Width 20 ns a

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Table 5 Optical Depth Retrieval and Its Associated Error, Target at 123 m , Gate Width 60 ns a

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Table 6 Comparison of Mean Readout and Dark Current Noise Values in Each Ring with 1 and 100 Laser Pulses Accumulated on the CCD Chip

Equations (14)

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N p π D 2 4 = 0.02.
τ target = 2 N p π D 2 4 = 0.04.
Δ P Norm ( θ i + 1 θ i ) = P D ( z c , θ i + 1 θ i , α b > 0 ) P s ( z c , θ s , α b > 0 ) P D ( z c , θ i + 1 θ i , α b = 0 ) P s ( z c , θ s , α b = 0 ) = 2 ϖ 0 b z a z b α b Δ L ( r , z , β i + 1 β i ) d z .
Δ L ( r , z , β i + 1 β i ) β i β i + 1 0 2 π p ( r , z , β ) sin β d β d φ ,
p ( β ) = A 2 π ω 0 b y 2 e A 1 2 y 2 β 2 ,
Δ P Norm ( θ i + 1 θ i ) = 2 τ A 2 A 1 2 { exp [ A 1 2 y 2 ( z c z c z ¯ ) 2 θ i 2 ] exp [ A 1 2 y 2 ( z c z c z ¯ ) 2 θ i + 1 2 ] } .
d eff = 1.30 2 λ π θ max , Log [ ln ( 1 + C t e ) 2 [ ( 1 + C t e ) 2 1 ] ] 0.5 z c z ¯ z c .
L ( β ) = 1 J 0 2 ( y sin ( β ) ) J 1 2 ( y sin ( β ) ) .
Δ L ( β i + 1 β i ) = J 0 2 ( y sin ( β i ) ) + J 1 2 ( y sin ( β i ) ) J 0 2 ( y sin ( β i + 1 ) ) J 0 2 ( y sin ( β i + 1 ) ) .
τ target = Δ P Norm ( θ i + 1 θ i ) T mask A 2 A 1 2 { exp [ A 1 2 y 2 ( z c z c z ) 2 θ i 2 ] exp [ A 1 2 y 2 ( z c z c z ) 2 θ i + 1 2 ] } .
τ target = ln ( P target ( θ min , z c ) P ref ( θ min , z c ) ) ,
σ read process / ring / laser pulse = 2 2 × number of pixels in a ring number of laser pulses accumulated on the CCD chip .
σ dark current / ring / laser pulse = dark current for a fixed exposure time × number of pixels in a ring number of laser pulses accumulated on the CCD chip during the exposure time .
σ intensification process / ring / laser pulse = 38 2 × 1 200 i = 1 number of pixels in a ring signal on   pixel i   ( in counts ) number of laser pulses accumulated on the CCD chip .

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