1. May 2001Venice Workshop1 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

2. May 2001Venice Workshop2 List of Themes How 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

3. May 2001Venice Workshop3 Automated DIMM Operation 35cm Telescope for the automated DIMM at the VLT Observatory Pixel size=0.7”Pixel size=0.7” Pupil Diameter=11cmPupil Diameter=11cm Pupil Separation=20cmPupil Separation=20cm Exposure Time=5msExposure Time=5ms 600 frames/mn600 frames/mn

4. May 2001Venice Workshop4 Fried parameter: ( meter,  ^6/5) Seeing: (arcsec,  ^-0.2) Optical Propagation The Signature of Atmospheric Turbulence

5. May 2001Venice Workshop5 Correlation time: Isoplanatic angle: High Resolution Imaging

6. May 2001Venice Workshop6 Statistics of Tau0 Comparison of wavefront velocity V0 and 200mb wind speed during Paranal and Gemini balloon campaigns V0 = 0.4 V 200mb

7. May 2001Venice Workshop7 Statistics of Tau0 Estimate of the coherence time from 200mb wind velocity during Paranal and Gemini balloon campaigns V0 fit = Max(V ground, 0.4 V 200mb ) Tau0 fit =0.31 r0/ V0 fit

8. May 2001Venice Workshop8 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) H bar =0.314 r0 / Theta0

9. Venice Workshop9 Statistics of Tau0 Geographical Location and 200mb wind velocity 16 years statistics ( line:0, dash:180, tr:La Silla, dia:Paranal, sq:Mauna Kea)

10. May 2001Venice Workshop10 Statistics of tau0 16-year average 200mb wind velocity at known observatories (Latitude and Longitude +/- 2.5 degree) ObservatoryJuneDecembermean Jun+Dec Chirripo (Costa Rica)17.810.314.1 Mauna Kea19.524.722.1 Gamsberg (Nam)32.020.026.0 Paranal34.522.228.4 La Silla36.027.631.8 La Palma24.042.633.3 Maidanak (Uz)27.149.636.4 San Pedro Martir 23.063.343.2

11. May 2001Venice Workshop11 Isoplanatic angle at zenith: Measuring teta0 with a DIMM Scintillation index at zenith:

12. May 2001Venice Workshop12 Measuring teta0 with a DIMM Choose an aperture such as: and

13. May 2001Venice Workshop13 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.

14. May 2001Venice Workshop14 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

15. May 2001Venice Workshop15 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

16. May 2001Venice Workshop16 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

17. May 2001Venice Workshop17 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

18. May 2001Venice Workshop18 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

19. May 2001Venice Workshop19 Statistics of tau0 and theta0 Paranal 2000 measurements at zenith, 0.5 micron, 10mn average Parameterbest 5%best 20%50%mean Seeing, arcsec0.430.560.750.86 200mb wind, m/s12192932 Tau0, ms8.55.83.63.9 Theta0, arcsec4.13.32.62.6