Models of the ground layer and free atmosphere at some sites
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Modelsof the ground layer and free atmosphere
at some sites
A. Tokovinin, CTIO
Need for OTP “models”: Adaptive Optics!
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OutlineOutline
Present MASS and DIMM MASS “overshoots” Free atmosphere model SODAR and balloons Ground layer model
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MASS = Multi-Aperture Scintillation Sensor
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/profilerhttp://www.ctio.noao.edu/~atokovin/profiler
MASS database: http://mass.ctio.noao.edu
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MASS-SCIDAR: MK2002
MASS-SCIDAR: MK2002
SCIDAR
MASS
PASP, 2005
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Combine MASS with DIMM GL
Combine MASS with DIMM GL
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MASS-DIMM instrumentsMASS-DIMM instruments
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MASS-DIMM + Meade
MASS-DIMM + Meade
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“Overshoots”
“Overshoots”
MASS
DIM
M
???Strong scintillationshould besaturated?
Cerro Pachon, 2003
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Strong scintillation
Strong scintillation
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Index distortion…
Index distortion…
Some over-correction for exp. time remains!
…and correction
…and correction
SAB SAB0/(1 + 0.7 SAB0)SAB SAB0/(1 + 0.7 SAB0)
J J0/(1 + 0.7 SAB)J J0/(1 + 0.7 SAB)
Semi-empiricalformula
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“Overshoots” corrected!
“Overshoots” corrected!
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MASS-DIMM: CP, 2005
MASS-DIMM: CP, 2005
MASS
DIM
M
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Histograms (CP, 2005)
Histograms (CP, 2005)
Tot
al
Gro
und
Free
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FA and GL are independent!FA and GL are independent!
1”
Can model FA and GL separately
Same plot for MK
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FA: calm or turbulent?
FA: calm or turbulent?
When free atmosphere
is calm, it is stable!When free atmosphere
is calm, it is stable!
Turbulence comes in bursts
Turbulence comes in bursts
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CP data overviewCP data
overview
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Data for Mauna Kea (2002)
Data for Mauna Kea (2002)
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OTP model: Pachon
OTP model: Pachon h,
kmGood Typ. Bad
0 2.2 2.7 3.3
0.5 0.2 0.4 0.7
1 0.03 0.1 0.2
2 0.02 0.1 0.4
4 0.2 0.4 0.6
8 0.15 0.2 0.3
16 0.25 0.3 0.3
All 3.05 4.2 5.8
Integrals, 10-13 m1/3
MASS-DIMM, 2005 0.62” 0.75” 0.91”
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Testing the model
Testing the model SAM AO system:
Rayleigh LGS at 10km+ 2 t-t NGS,45 Zernike modes
SAM AO system:Rayleigh LGS at 10km+ 2 t-t NGS,45 Zernike modes
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SODAR campaign at CP
SODAR campaign at CP
Goal: define the thickness of the Ground Layer
Duration: Oct. 30 to Nov. 15, 2004Equipment: XFAS from Scintec
Altitude range: 40m – 800mVertical resolution: 20mTime resolution: 20 min.
Results: 505 profiles (168 hours)
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SODAR profilesSODAR profiles
Nov 3 Nov 4
Nov 5 Nov 6
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SODAR vs. MASS-DIMM (CTIO)SODAR vs. MASS-DIMM (CTIO)
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GL model: SODARGL model: SODAR
best 25%
typicalworst 25%
Split data in groups and average separately!
Cn2(h) = A e-h/h0 + B e-h/h1Cn
2(h) = A e-h/h0 + B e-h/h1Abahamid et al.:
Cn2(h) = A h-1.5
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GL model: balloons
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
43 profiles
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What is “seeing”?What is
“seeing”?Seeing isthe HF powerof opticalturbulence (J)expressedin “arcseconds”[Kolmogorov]
Seeing isthe HF powerof opticalturbulence (J)expressedin “arcseconds”[Kolmogorov]
” = (J / 6.8x10-13)3/5
Do not mix “seeing” with image quality!Do not mix “seeing” with image quality!
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Atmospheric IQ at Pachon (2005)
Atmospheric IQ at Pachon (2005)
medianworst 25%
best 25%
L0 =25m
Seeing
Why do we use “seeing”? – to avoid a mess!Why do we use “seeing”? – to avoid a mess!
CP site monitorDec 2004-Apr 2005
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ConclusionsConclusions
We know integrals in FA and GL and their variationFA and GL are independentTurbulence in FA: lower when stronger Periods of calm FA: “sweet spot” for AO!Profile models for CP: good, typical, badGL: exponential models