Abstract

Temporal fluctuations of the atmospheric piston are critical for interferometers as they determine their sensitivity. We characterize an instrumental setup, termed the piston scope, that aims at measuring the atmospheric time constant, τ0, through the image motion in the focal plane of a Fizeau interferometer. High-resolution piston scope measurements have been obtained at the observatory of Paranal, Chile in April 2006. The derived atmospheric parameters are shown to be consistent with data from the astronomical site monitor, provided that the atmospheric turbulence is displaced along a single direction. The piston scope measurements of lower temporal and spatial resolution were recorded for what is believed to be the first time in February 2005 at the Antarctic site of Dome C. Their reanalysis in terms of the new data calibration sharpens the conclusions of a first qualitative examination [Appl. Opt. 45, 5709 (2006)].

© 2007 Optical Society of America

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References

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  1. A. Kellerer and A. Tokovinin, "Atmospheric coherence time in interferometry: definition and measurement," Astron. Astrophys. 461, 775-781 (2007).
    [CrossRef]
  2. A. Kellerer, M. Sarazin, V. Coudé Du Foresto, K. Agabi, E. Aristidi, and T. Sadibekova, "A method of estimating time scales of atmospheric piston and its application at Dome C (Antarctica)," Appl. Opt. 45, 5709-5715 (2006).
    [CrossRef] [PubMed]
  3. J. M. Conan, G. Rousset, and P. Y. Madec, "Wave-front spectra in high-resolution imaging through turbulence," J. Opt. Soc. Am. A 12, 1559-1570 (1995).
    [CrossRef]
  4. T. Butterley, R. Wilson, and M. Sarazin, "Determination of the profile of atmospheric optical turbulence strength from SLODAR data," Mon. Not. R. Astron. Soc. 369, 835-845 (2006).
    [CrossRef]
  5. M. Sarazin and F. Roddier, "The ESO differential image motion monitor," Astron. Astrophys. 227, 294-300 (1990).
  6. M. Sarazin and A. Tokovinin, "The statistics of isoplanatic angle and adaptive optics time constant derived from DIMM data," in Beyond Conventional Adaptive Optics, S. Esposito and R. Ragazzoni, eds., Vol. 58 of ESO Conference and Workshop Proceedings (European Southern Observatory, 2001), pp. 321-328.
  7. European Centre for Medium-Range Weather Forecasts, http://www.ecmwf.int/.
  8. J. Lawrence, M. Ashley, A. Tokovinin, and T. Travouillon, "Exceptional astronomical seeing conditions above Dome C in Antarctica," Nature 431, 278-281 (2004).
    [CrossRef] [PubMed]
  9. A. Tokovinin, National Optical Astronomy Observatory: MASS presentation, http://www.ctio.noao.edu/∼atokovin/profiler/(2006).

2007 (1)

A. Kellerer and A. Tokovinin, "Atmospheric coherence time in interferometry: definition and measurement," Astron. Astrophys. 461, 775-781 (2007).
[CrossRef]

2006 (2)

A. Kellerer, M. Sarazin, V. Coudé Du Foresto, K. Agabi, E. Aristidi, and T. Sadibekova, "A method of estimating time scales of atmospheric piston and its application at Dome C (Antarctica)," Appl. Opt. 45, 5709-5715 (2006).
[CrossRef] [PubMed]

T. Butterley, R. Wilson, and M. Sarazin, "Determination of the profile of atmospheric optical turbulence strength from SLODAR data," Mon. Not. R. Astron. Soc. 369, 835-845 (2006).
[CrossRef]

2004 (1)

J. Lawrence, M. Ashley, A. Tokovinin, and T. Travouillon, "Exceptional astronomical seeing conditions above Dome C in Antarctica," Nature 431, 278-281 (2004).
[CrossRef] [PubMed]

1995 (1)

1990 (1)

M. Sarazin and F. Roddier, "The ESO differential image motion monitor," Astron. Astrophys. 227, 294-300 (1990).

Appl. Opt. (1)

Astron. Astrophys. (2)

M. Sarazin and F. Roddier, "The ESO differential image motion monitor," Astron. Astrophys. 227, 294-300 (1990).

A. Kellerer and A. Tokovinin, "Atmospheric coherence time in interferometry: definition and measurement," Astron. Astrophys. 461, 775-781 (2007).
[CrossRef]

J. Opt. Soc. Am. A (1)

Mon. Not. R. Astron. Soc. (1)

T. Butterley, R. Wilson, and M. Sarazin, "Determination of the profile of atmospheric optical turbulence strength from SLODAR data," Mon. Not. R. Astron. Soc. 369, 835-845 (2006).
[CrossRef]

Nature (1)

J. Lawrence, M. Ashley, A. Tokovinin, and T. Travouillon, "Exceptional astronomical seeing conditions above Dome C in Antarctica," Nature 431, 278-281 (2004).
[CrossRef] [PubMed]

Other (3)

A. Tokovinin, National Optical Astronomy Observatory: MASS presentation, http://www.ctio.noao.edu/∼atokovin/profiler/(2006).

M. Sarazin and A. Tokovinin, "The statistics of isoplanatic angle and adaptive optics time constant derived from DIMM data," in Beyond Conventional Adaptive Optics, S. Esposito and R. Ragazzoni, eds., Vol. 58 of ESO Conference and Workshop Proceedings (European Southern Observatory, 2001), pp. 321-328.

European Centre for Medium-Range Weather Forecasts, http://www.ecmwf.int/.

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Figures (9)

Fig. 1
Fig. 1

Structure functions of the fringe position relative to the combined Airy disks for an interferometer with mirror diameters D and baseline length B. The atmosphere is assumed to consist of a single layer displaced with wind speed V at an angle α from the baseline. The values of α are indicated in the bottom right box.

Fig. 2
Fig. 2

Example of an image recorded with 1 ms exposure time at Paranal on the night of 23–24 April 2006 at 02:03:55 UT and fitted intensity profile along the axial direction.

Fig. 3
Fig. 3

Theoretical structure functions (dashed curve) fitted onto data obtained at Paranal, the resulting seeing ϵ 0 , velocity V, wind orientation α, and coherence time τ 0 are indicated.

Fig. 4
Fig. 4

Seeing values measured at Paranal with the DIMM and the piston scope. The uncertainties of the piston scope values correspond to a twofold increase in the quality of the data adjustment.

Fig. 5
Fig. 5

Wavefront velocities obtained with the piston scope ( V ps ) , wind velocities measured by sensors at 30   m above the ground of Paranal ( V g ) and interpolated at 200   mB from ECMWF data ( V 200   mB ) .

Fig. 6
Fig. 6

Coherence times obtained at Paranal through three different methods.

Fig. 7
Fig. 7

(Color online) Profiles of the free atmosphere turbulence obtained by MASS at Paranal. On 22–23 April (left panel) 2006 the turbulence was contained in several layers of similar intensity, while on 23–34 April (right panel) one layer at 4   km was predominant at approximately 2:00 UT.

Fig. 8
Fig. 8

Atmospheric parameter values derived from measurements at Dome C.

Fig. 9
Fig. 9

Seeing values measured at Dome C with the DIMM and the piston scope.

Equations (11)

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W φ ( f ) = 0.00969 k 2 0 + f 11 / 3 C n 2 d h ,
M ˜ ( f ) = λ / ( 2 π ) A ( f ) FT [ ( δ B δ 0 ) / B ( δ B + δ 0 ) / 2 d / d x ] ( f ) ,
M ˜ ( f ) = λ / ( 2 π ) A ( f ) [ 2   sin ( π f B ) 2 π f B   cos ( π f B ) ] / B ,
W ϕ ( f ) = M ˜ 2 ( f ) W φ ( f ) .
w ϕ ( ν ) = 1 V + W ϕ ( f x   cos   α + f y   sin   α , f y   cos   α f x   sin   α ) d f y .
D ϕ ( t ) = 2 + ( 1 cos ( 2 π ν t ) ) w ϕ ( ν ) d ν ,
= 2 × 0.00969 C n 2 d h / B 2 0 + f 8 / 3 ( 2 J 1 ( π f d ) / ( π f d ) ) 2 d f × 0 2 π ( 1 cos ( 2 π f   cos ( θ + α ) V t ) ) [ 2   sin ( π B f   cos   θ ) 2 π f B   cos   θ   cos ( π f B   cos   θ ) ] 2 d θ .
D ϕ ( t τ 0 ) r 0 5 / 3 0 + π C n 2 d h ,
V ps V ¯ 5 / 3 = [ 0 + V ( h ) 5 / 3 C n 2 ( h ) d h 0 + C n 2 ( h ) d h ] 3 / 5 .
V ¯ 5 / 3 max ( V g , 0.4 V 200   mB ) .
D ϕ ( t ) = D ϕ ( t t c ) × ( 1 exp ( ( t / t c ) 5 / 3 ) ) . 

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