SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING
description
Transcript of SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING
![Page 1: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/1.jpg)
SITE PARAMETERS RELEVANT FOR
HIGH RESOLUTION IMAGING
Marc Sarazin
European Southern Observatory
![Page 2: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/2.jpg)
2Zanjan, July 2001
List of Themes Optical Propagation through Turbulence
– Mechanical and Thermal effects
– Index of Refraction
– Signature on ground based observations
– Correction methods Integral monitoring Techniques
– Seeing Monitoring
– Scintillation Monitoring Profiling Techniques
– Instrumented Masts
– Balloon Borne Sensors
– Scintillation Ranging Modelling Techniques Conclusions - How to find the ideal site...and keep it good?
![Page 3: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/3.jpg)
3Zanjan, July 2001
Fried parameter: ( meter, ^6/5)
Seeing: (arcsec, ^-0.2) 0
98.0)(r
FWHM
53
0
22
0 )()sec(2
423.0)(
dhhCr n
Optical Propagation
The Signature of Atmospheric Turbulence
Easy to remember: r0=10cmFWHM=1” in the visible (0.5m)
![Page 4: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/4.jpg)
4Zanjan, July 2001
Optical Propagation
The Signature of Atmospheric Turbulence
S= 0.7 à 2.2 um FWHM=0.056 “
S=0.3 à 2.2 um FWHM=0.065 “
0I
IS
0rFWHM
Seeing = FWHM
Strehl Ratio
![Page 5: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/5.jpg)
5Zanjan, July 2001
Optical Propagation
The Signature of Atmospheric Turbulence
A Speckle structure appears when the exposure is shorter than the atmosphere coherence time 0
1ms exposure at the focus of a large telescope
v
r031.0
![Page 6: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/6.jpg)
6Zanjan, July 2001
53
0
22
0 )()()sec(2
91.2)( 35
dhhChv n
53
0
22
0 )()sec(2
91.2)( 35
dhhCh n
Correlation time:
Isoplanatic angle:
High Resolution Imaging
![Page 7: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/7.jpg)
7Zanjan, July 2001
High Resolution Imaging
Active or Adaptive optics?
dc 0.01 0.1 1 10 100 Temporalfrequency
(Hz)
Spatial
frequency
1/D
10/D
GravityThermal
Local
air
Wind
Atmosphere
D: Diameter ofthe telescope
Figuring
Active Optics Adaptive optics
0.1/D
Active optics can correct large amplitudes on slowly varying effects of smaller spatial frequency
![Page 8: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/8.jpg)
8Zanjan, July 2001
High Resolution Imaging
Correction Methods based on
Adaptive Optics use
natural or artificial
reference stars for wave front
sensing
![Page 9: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/9.jpg)
9Zanjan, July 2001
High Resolution Imaging
Small Field Correction by
adaptive optics(simulation by M. Le Louarn, ESO)
![Page 10: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/10.jpg)
10Zanjan, July 2001
High Resolution Imaging
Correction Methods
based on
Adaptive Optics:
Anisoplanatismsets a limit to the
distance of the reference star
Strehl=0.38 at =0
Reference Star
Télescope
ScienceObject
Turbulence
Common Atmospheric Path
![Page 11: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/11.jpg)
11Zanjan, July 2001
Atmospheric Turbulence
Poor sky coverage with natural guide stars
![Page 12: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/12.jpg)
12Zanjan, July 2001
High Resolution Imaging
![Page 13: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/13.jpg)
13Zanjan, July 2001
High Resolution Imaging
Wide Field Correction by
adaptive optics(simulation by
R.Rigaut, Gemini project)
(A)
Uncorrected Field, showing speckle structure and global image motion
![Page 14: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/14.jpg)
14Zanjan, July 2001
High Resolution Imaging
Wide Field Correction by
adaptive optics(simulation by
R.Rigaut, Gemini project)
(B)
Single guide star in the center of the field
![Page 15: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/15.jpg)
15Zanjan, July 2001
High Resolution Imaging
Wide Field Correction by
adaptive optics(simulation by
R.Rigaut, Gemini project)
(C)
Multiple guide stars
(one per field corner)
![Page 16: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/16.jpg)
16Zanjan, July 2001
Atmospheric Turbulence
![Page 17: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/17.jpg)
![Page 18: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/18.jpg)
![Page 19: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/19.jpg)
19Zanjan, July 2001
Performances of Adaptive Optics Correction
Finite number of actuator (fitting error):
2fit=0.34 (D/ro)5/3
Finite number of sub apertures (spatial aliasing)
2al=0.17 (D/ro)5/3
Finite lag between measure and actions:
2sl~ (fg/f3dB)5/3 fg=1/ o
Noise in the measurements:
2m~1/(Nph.ro
2.o)5/3
Wave front from object and guide star cross different layers sections (anisoplanatism): 2
isop~(/ o)5/3
Total error variance: 2tot =2
fit +2al +2
sl +2m +2
isop
Strehl~exp(- 2tot)
Atmospheric Turbulence
![Page 20: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/20.jpg)
20Zanjan, July 2001
The new tools for site surveys
The development of new automated monitoring instruments is necessary, in particular:
•Sky monitor-CONCAM (Kitt Peak): cloud imager, fisheye lens, ST8 CCD on a fixed mount-IR All-Sky camera (APO-SLOAN):cloud imager, scanning mirror, 10-11.4m filter, pyroelectric detector-All Sky Imager (ESO project): wide field photometry of reference stars, 50mm lens, BVI filters, 2kx2k CCD on a scanning mount.
•Sodium Layer Monitor?
•Portable (single star?) turbulence profiler
![Page 21: SITE PARAMETERS RELEVANT FOR HIGH RESOLUTION IMAGING](https://reader035.fdocuments.net/reader035/viewer/2022062422/56813fd0550346895daab1e6/html5/thumbnails/21.jpg)
21Zanjan, July 2001
The new tools for site surveys
The development of new automated monitoring instruments is necessary, in particular: