MASS-DIMM and SODAR at Cerro Pachon A. Tokovinin Gemini, May 3, 2005

Outline “Seeing” and delivered image quality MASS-DIMM instrument Free atmosphere and Ground layer Detailed GL models from SODAR Operational use of MASS-DIMM data Gemini, May 3, 2005

Contributors to DIQ Gemini, May 3, 2005

What is “seeing”? ” = (J / 6.8x10-13)3/5 Seeing is the HF power of optical turbulence (J) expressed in “arcseconds” [Kolmogorov] ” = (J / 6.8x10-13)3/5 Gemini, May 3, 2005

Atmospheric IQ at Pachon Seeing worst 25% median best 25% L0 =25m CP site monitor Dec 2004-Apr 2005 Why do we use “seeing”? – to avoid a mess! Gemini, May 3, 2005

What is MASS? 6-layer model Weighting functions 4 normal indices 6 diff. indices PROFILE Gemini, May 3, 2005

Restoration of profile Response is “triangular” Good integrals (βf, θ0) S/N~10% (better sensitivity at low turbulence) http://www.ctio.noao.edu/~atokovin/profiler Gemini, May 3, 2005

Combine MASS with DIMM! Gemini, May 3, 2005

MASS-DIMM instruments Gemini, May 3, 2005

MASS-DIMM + Meade Gemini, May 3, 2005

MASS-DIMM: details 5.5mm diam. Gemini, May 3, 2005

Measured parameters Seeing β (Fried parameter) Free-atmosphere seeing βf Isoplanatic angle θ0 AO time constant τ0 (without ground layer, but…) Low-resolution profile: 6 layers at 0.5,1,2,4,8,16km NOT MEASURED: Outer scale, detailed profile, wind MASS database: http://mass.ctio.noao.edu Gemini, May 3, 2005

MASS-DIMM expansion TMT site-testing program (6) Chilean observatories (3) ESO 1 (+5) Antarctica (1) Palomar (1+) … 2002-2005: 3 years Gemini, May 3, 2005

What can go wrong with CP site monitor? MASS: Low flux Cirrus cloud Dirty optics Bad alignment Wrong param. Overshoots DIMM: Bad focus (over-estimate seeing) Pointing problems Wind shake Un-friendly control Join DIMM and MASS data in the common database! Gemini, May 3, 2005

“Overshoots” Gemini, May 3, 2005

Strong scintillation Gemini, May 3, 2005

MASS-DIMM: CP, 2005 DIMM MASS Gemini, May 3, 2005

Histograms Free Ground Total Gemini, May 3, 2005

FA and GL are independent! artifacts Gemini, May 3, 2005

FA: calm or turbulent? Turbulence comes in bursts When free atmosphere is calm, it is stable! Gemini, May 3, 2005

Free atmosphere in detail Strong turbulence = low altitude Gemini, May 3, 2005

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) Gemini, May 3, 2005

SODAR profiles Nov 3 Nov 4 Nov 6 Nov 5 Gemini, May 3, 2005

SODAR vs. MASS-DIMM Gemini, May 3, 2005

GL model worst 25% typical best 25% Gemini, May 3, 2005

GL model: balloons J, 10-13 m1/3 h(1/e), m Good 0.9-1.2 15-30 Typical 1.6-3 20-40 Bad 6.5-10 50-100 Gemini, May 3, 2005

CP model The model is an independent combination of FA and GL. FA: one layer with changing strength and altitude. GL: exponential model 25% 50% 75% FA 0.29 0.41 0.56 GL 0.53 0.67 Total 0.63 0.77 0.91 Gemini, May 3, 2005

Operational use of MASS-DIMM data Periods of calm (<0.3”) FA (25%): extreme value for AO! (can be predicted from jet stream?) MASS gives on-line isoplanatic angle and AO time constant select critical/non-critical AO programs Periods of bad (>1”) FA seeing (5%): hopeless! use telescope as a “light bucket” for spectroscopy GL seeing can be as bad as 1” (under strong wind?) will be corrected by GLAO! Match DIQ to site seeing (critical in IR) Good seeing: product of FA and GL probabilities Bad seeing: sum of FA and GL probabilities Gemini, May 3, 2005

Last FA-calm night: May1/2, 2005 The “sweet spot” for AO! Gemini, May 3, 2005