Upload
buddy-stokes
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Vancouver, June 2005 1
Modelsof the ground layer and free atmosphere
at some sites
A. Tokovinin, CTIO
Need for OTP “models”: Adaptive Optics!
Vancouver, June 2005 2
OutlineOutline
Present MASS and DIMM MASS “overshoots” Free atmosphere model SODAR and balloons Ground layer model
Vancouver, June 2005 3
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
Vancouver, June 2005 4
MASS-SCIDAR: MK2002
MASS-SCIDAR: MK2002
SCIDAR
MASS
PASP, 2005
Vancouver, June 2005 5
Combine MASS with DIMM GL
Combine MASS with DIMM GL
Vancouver, June 2005 6
MASS-DIMM instrumentsMASS-DIMM instruments
Vancouver, June 2005 7
MASS-DIMM + Meade
MASS-DIMM + Meade
Vancouver, June 2005 8
“Overshoots”
“Overshoots”
MASS
DIM
M
???Strong scintillationshould besaturated?
Cerro Pachon, 2003
Vancouver, June 2005 9
Strong scintillation
Strong scintillation
Vancouver, June 2005 10
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
Vancouver, June 2005 11
“Overshoots” corrected!
“Overshoots” corrected!
Vancouver, June 2005 12
MASS-DIMM: CP, 2005
MASS-DIMM: CP, 2005
MASS
DIM
M
Vancouver, June 2005 13
Histograms (CP, 2005)
Histograms (CP, 2005)
Tot
al
Gro
und
Free
Vancouver, June 2005 14
FA and GL are independent!FA and GL are independent!
1”
Can model FA and GL separately
Same plot for MK
Vancouver, June 2005 15
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
Vancouver, June 2005 16
CP data overviewCP data
overview
Vancouver, June 2005 17
Data for Mauna Kea (2002)
Data for Mauna Kea (2002)
Vancouver, June 2005 18
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”
Vancouver, June 2005 19
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
Vancouver, June 2005 20
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)
Vancouver, June 2005 21
SODAR profilesSODAR profiles
Nov 3 Nov 4
Nov 5 Nov 6
Vancouver, June 2005 22
SODAR vs. MASS-DIMM (CTIO)SODAR vs. MASS-DIMM (CTIO)
Vancouver, June 2005 23
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
Vancouver, June 2005 24
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
Vancouver, June 2005 25
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!
Vancouver, June 2005 26
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
Vancouver, June 2005 27
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