The GSM: a dedicated monitor for wavefront optical parameter measurements

The EOS/SPIE Symposium on Remote Sensing - Sept. 1999 - Florence

A. ZiadDépartement d’Astrophysique - Parc Valrose - 06108 NICE Cedex 2 - France

The GSM: a dedicated monitor for wavefront

optical parameter measurements

GSM working layout at La Silla (Chile) Sept. 1997

A. Ziad,

F. Martin,

R. Conan,

J. Borgnino.


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Summary

Presentation of the GSM Principle Configuration and optical device

Atmospheric optical parameters (AOP) data Data of the outer scale L0, seeing and isoplanatic

angle measured at different sites over the world:

La Silla, Pachon, Paranal (Chile), Oukaïmeden (Morocco) and Maydanak (Uzbekistan)


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Presentation of the GSM

GSM is equipped with 4 telescopes : each one measures synchronously the angle of arrival (AA) of the wavefront spatial covariance L0 differential variance

scintillation

spatio-temporal correlation

GSM working layout at La Silla (Chile) Sept. 1997


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The GSM optical device

)(tan2

1 1

CA

BD


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GSM campaigns

GSM is operational since 2 years and different sites over the world has been visited

La Silla, Pachon, Paranal (Chile) Oukaïmeden (Morocco) Maydanak (Uzbekistan)


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Typical one night measurements

L0med = 45.3 m

0med = 0.99’’

0med = 1.7’’


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GSM/DIMM comparison

Surface layer effect:

GSM was installed at a height of 1.7 m.

DIMM was installed at a height of 5 m.

Exposure time effect:

5 ms for GSM 10 ms for DIMM


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Effect of the exposure time

Linear extrapolation is done to evaluate the differential variance at the origine

d2(0ms) = 2 d

2(5ms) - d2(10ms)


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L0, & resultsLa Silla (Chile) Aug. 28 - Sept. 18 1997

L0med = 25 m

0med = 1.68’’

0med = 1.26’’


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L0, & resultsOukaïmeden (Morocco) April 10-25

1998

L0med = 32 m

0med = 1.33’’

0med = 1.50’’


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L0, & resultsMaydanak (Uzbekistan) July 16-24 1998

L0med = 26 m

0med = 0.66’’

0med = 2.48’’


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L0, & resultsCerro Pachon (Chile) Oct. 1-10 1998

L0med = 27 m

0med = 0.83’’

0med = 2.82’’


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L0, & resultsParanal (Chile) Nov. 26 - Dec. 21 1998

L0med = 22 m

0med = 0.88’’

0DIMM = 0.87’’

0med = 1.9’’


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Data summary

Site Date Seeing 0 (as) Outer scale L0 (m) Isoplanatic angle 0 (as)

La Silla (Chile) 08/26/97 - 09/20/97 1.68 +/- 0.47 24.8 +/- 19.3 1.26 +/- 0.42

Oukaimeden (Morocco) 04/10/98 - 04/25/98 1.33 +/- 0.90 31.1 +/- 34,8 1.50 +/- 0.69

Maydanak (Uzbekistan) 07/16/98 - 07/25/98 0.66 +/- 0.25 25.9 +/- 19.0 2.48 +/- 0.70

Cerro Pachon (Chile) 10/02/98 - 10/09/98 0.83 +/- 0.46 26.7 +/- 3.5 2.82 +/- 0.97

Paranal (Chile) 11/27/98 - 12/20/98 0.88 +/- 0.40 22.1 +/- 33.9 1.90 +/- 0.69


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Temporal stability of the AOP

For an error of 5%, the change time is:

for the outer scale: 1.6 mn for the seeing: 9.2 mn for the isoplanatic angle: 4.6

mn

)()(

)()(

tXttX

tXttXNDX


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Conclusion

GSM is operational since 2 years 5 campaigns:

La Silla, Cerro Pachon, Paranal (Chile), Oukaïmden (Morocco) and Maydanak (Uzbekistan).

Important databank of the different sites over the world: Study of the temporal variability of the AOP and their

prediction via a modelization to optimize the HAR observations

Results on the Web: http://www-astro.unice.fr/GSM

Documents

The GSM: a dedicated monitor for wavefront optical parameter measurements