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The Statistics of Isoplanatic Angle and Adaptive Optics Time Constant derived from DIMM data

The Statistics of Isoplanatic Angle and Adaptive Optics Time Constant derived from DIMM data. Marc Sarazin (1) and Andrei Tokovinine (2) (1) European Southern Observatory (2) Cerro Tololo Inter-American Observatory. List of Themes How to find the ideal site...and keep it good?.

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The Statistics of Isoplanatic Angle and Adaptive Optics Time Constant derived from DIMM data

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  1. The Statistics of Isoplanatic Angle and Adaptive Optics Time Constant derived from DIMM data Marc Sarazin (1) and Andrei Tokovinine (2) (1) European Southern Observatory (2) Cerro Tololo Inter-American Observatory Venice Workshop

  2. List of ThemesHow to find the ideal site...and keep it good? • Optical Propagation through Turbulence • Mechanical and Thermal • Index of Refraction • Signature on ground based observations • Correction methods • Integral Monitoring Techniques • Seeing Monitoring • Scintillation Monitoring • Profiling Techniques • Microthermal Sensors • Scintillation Ranging • Modelling Techniques Venice Workshop

  3. Automated DIMM Operation 35cm Telescope for the automated DIMM at the VLT Observatory • Pixel size=0.7” • Pupil Diameter=11cm • Pupil Separation=20cm • Exposure Time=5ms • 600 frames/mn Venice Workshop

  4. Optical PropagationThe Signature of Atmospheric Turbulence Seeing: (arcsec, ^-0.2) Fried parameter: ( meter, ^6/5) Venice Workshop

  5. High Resolution Imaging Correlation time: Isoplanatic angle: Venice Workshop

  6. Statistics of Tau0 Comparison of wavefront velocity V0 and 200mb wind speed during Paranal and Gemini balloon campaigns V0 = 0.4 V200mb Venice Workshop

  7. Statistics of Tau0 Estimate of the coherence time from 200mb wind velocity during Paranal and Gemini balloon campaigns V0fit= Max(Vground, 0.4 V200mb) Tau0fit=0.31 r0/ V0fit Venice Workshop

  8. Statistics of Tau0 The error on the estimate of the coherence time from 200mb wind velocity increases when low level turbulence dominates (Paranal and Gemini balloon campaigns) Hbar =0.314 r0 / Theta0 Venice Workshop

  9. Statistics of Tau0 Geographical Location and 200mb wind velocity 16 years statistics ( line:0, dash:180, tr:La Silla, dia:Paranal, sq:Mauna Kea) Venice Workshop

  10. Statistics of tau0 16-year average 200mb wind velocity at known observatories (Latitude and Longitude +/- 2.5 degree) Observatory June December mean Jun+Dec Chirripo (Costa Rica) 17.8 10.3 14.1 Mauna Kea 19.5 24.7 22.1 Gamsberg (Nam) 32.0 20.0 26.0 Paranal 34.5 22.2 28.4 La Silla 36.0 27.6 31.8 La Palma 24.0 42.6 33.3 Maidanak (Uz) 27.1 49.6 36.4 San Pedro Martir 23.0 63.3 43.2 Venice Workshop

  11. Measuring teta0 with a DIMM Isoplanatic angle at zenith: Scintillation index at zenith: Venice Workshop

  12. Measuring teta0 with a DIMM Choose an aperture such as: and Venice Workshop

  13. Statistics of Theta0 Chromatic effects Comparison of scintillation index and isoplanatic angle for Paranal Cn2 profiles at various wavelengths (0,4, 0.5, 0.7, and 0.9 micron, top to bottom) The dispersion from the linear relation is about 5%. The chromatic error at 0.5 micron is [+2%,-5%] from 0.4 to 0.9 micron. Venice Workshop

  14. Statistics of Theta0 Time Averaging Effects True bias from 200mb wind speed for Paranal Cn2 profiles compared to bias calculated from a single-layer model The best agreement is obtained using half the wind velocity at 200mb. The mean correction due to time averaging was 12% in 2000 with the 5ms Paranal DIMM Venice Workshop

  15. Statistics of Tau0 and Theta0 Statistical Distribution of the seeing at Paranal in 2000 mean r0=11.6cm for photometric sky observations at 0.5 micron and at zenith, averaged over 10mn Venice Workshop

  16. Statistics of Tau0 Statistical Distribution of the coherence time at Paranal in 2000 mean tau0=3.9ms for photometric sky observations at 0.5 micron and at zenith, averaged over 10mn Venice Workshop

  17. Statistics of Theta0 Statistical Distribution of the isoplanatic angle at Paranal in 2000 mean Theta0=2.6” for photometric sky observations at 0.5 micron and at zenith, averaged over 10mn Venice Workshop

  18. Statistics of Tau0 and Teta0 Statistical Distribution of the isoplanatic angle at Paranal in 2000 for high and low wind speed at the tropopause The mean Theta0 increases by 10% for each 10m/s speed decrease The mean Tau0 is 30% larger for the best 50% values of Theta0 Venice Workshop

  19. Statistics of tau0 and theta0 Paranal 2000 measurements at zenith, 0.5 micron, 10mn average Parameter best 5% best 20% 50% mean Seeing, arcsec 0.43 0.56 0.75 0.86 200mb wind, m/s 12 19 29 32 Tau0, ms 8.5 5.8 3.6 3.9 Theta0, arcsec 4.1 3.3 2.6 2.6 Venice Workshop

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