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Models of the ground layer and free atmosphere at some sites

Models of the ground layer and free atmosphere at some sites. A. Tokovinin, CTIO. Need for OTP “models”: Adaptive Optics!. Outline. Present MASS and DIMM MASS “overshoots” Free atmosphere model SODAR and balloons Ground layer model. MASS = Multi-Aperture Scintillation Sensor.

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Models of the ground layer and free atmosphere at some sites

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  1. Modelsof the ground layer and free atmosphereat some sites A. Tokovinin, CTIO Need for OTP “models”: Adaptive Optics! Vancouver, June 2005

  2. Outline • Present MASS and DIMM • MASS “overshoots” • Free atmosphere model • SODAR and balloons • Ground layer model Vancouver, June 2005

  3. MASS = Multi-Aperture Scintillation Sensor • 6 “layers” with triangular response • Good integrals • AO time constant • S/N~10% (better sensitivity at low turbulence) http://www.ctio.noao.edu/~atokovin/profiler MASS database: http://mass.ctio.noao.edu Vancouver, June 2005

  4. MASS-SCIDAR: MK2002 SCIDAR PASP, 2005 MASS Vancouver, June 2005

  5. Combine MASS with DIMM  GL Vancouver, June 2005

  6. MASS-DIMM instruments Vancouver, June 2005

  7. MASS-DIMM + Meade Vancouver, June 2005

  8. “Overshoots” DIMM ??? Strong scintillation should be saturated? MASS Cerro Pachon, 2003 Vancouver, June 2005

  9. Strong scintillation Vancouver, June 2005

  10. Index distortion… …and correction Semi-empirical formula SAB SAB0/(1 + 0.7 SAB0) Some over-correction for exp. time remains! J  J0/(1 + 0.7 SAB) Vancouver, June 2005

  11. “Overshoots” corrected! Vancouver, June 2005

  12. MASS-DIMM: CP, 2005 DIMM MASS Vancouver, June 2005

  13. Histograms (CP, 2005) Ground Free Total Vancouver, June 2005

  14. FA and GL are independent! 1” Same plot for MK Can model FA and GL separately Vancouver, June 2005

  15. FA: calm or turbulent? Turbulence comes in bursts When free atmosphere is calm, it is stable! Vancouver, June 2005

  16. CP data overview Vancouver, June 2005

  17. Data for Mauna Kea (2002) Vancouver, June 2005

  18. OTP model: Pachon Integrals, 10-13 m1/3 0.62” 0.75” 0.91” MASS-DIMM, 2005 Vancouver, June 2005

  19. SAM AO system: Rayleigh LGS at 10km + 2 t-t NGS, 45 Zernike modes Testing the model Vancouver, June 2005

  20. SODAR campaign at CP • Goal: define the thickness of • the Ground Layer • Duration: Oct. 30 to Nov. 15, 2004 • Equipment: XFAS from Scintec • Altitude range: 40m – 800m • Vertical resolution: 20m • Time resolution: 20 min. • Results: 505 profiles (168 hours) Vancouver, June 2005

  21. SODAR profiles Nov 3 Nov 4 Nov 6 Nov 5 Vancouver, June 2005

  22. SODAR vs. MASS-DIMM (CTIO) Vancouver, June 2005

  23. GL model: SODAR Split data in groups and average separately! worst 25% typical best 25% Cn2(h) = A e-h/h0 + B e-h/h1 Abahamid et al.: Cn2(h) = A h-1.5 Vancouver, June 2005

  24. GL model: balloons 43 profiles Vancouver, June 2005

  25. What is “seeing”? Seeing is the HF power of optical turbulence (J) expressed in “arcseconds” [Kolmogorov] ” = (J / 6.8x10-13)3/5 Do not mix “seeing” with image quality! Vancouver, June 2005

  26. Atmospheric IQ at Pachon (2005) Seeing worst 25% median best 25% L0 =25m CP site monitor Dec 2004-Apr 2005 Why do we use “seeing”? – to avoid a mess! Vancouver, June 2005

  27. Conclusions • We know integrals in FA and GL and their variation • FA and GL are independent • Turbulence in FA: lower when stronger • Periods of calm FA: “sweet spot” for AO! • Profile models for CP: good, typical, bad • GL: exponential models Vancouver, June 2005

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