Download using the scintillation of extended objects to probe lower

USING THE SCINTILLATION OF
EXTENDED OBJECTS TO PROBE
LOWER ATMOSPHERIC TURBULENCE
Concept & First Results Published in:
Experimental Astronomy 12, 1, 2001
Jacques M. Beckers
US National Solar Observatory
“SHADOW BANDS” DURING SOLAR ECLIPSE
Images taken by Franz Kerschbaum (Vienna) during 2006 eclipse
~ 60 cm
¾ CLOSE TO “TOTALITY” AT A TOTAL ECLIPSE OF THE SUN RAPIDLY VARYING, LOW
CONTRAST LIGHT PATTERNS ARE SEEN ON THE GROUND OR BUILDINGS.THESE ARE
REFERRED TO AS “SHADOW BANDS”. IT IS THE SAME AS SOLAR SCINTILLATION.
¾ SHADOW BAND PATTERN IS ELONGATED IN THE DIRECTION OF THE CRESCENT
¾ CONTRAST APPEARS TO VARY FROM ECLIPSE TO ECLIPSE AND PROBABLY WITH LOCATION
¾ IT IS CLEARLY A PHENOMENON ASSOCIATED WITH ATMOSPHERIC TURBULENCE
¾ ED SEYKORA DETERMINED IN 1993 THAT PHENOMENON IS ALSO PRESENT OUTSIDE SOLAR
ECLIPSE BUT WITH MUCH LOWER CONTRAST ( ≤ 0.1 % RMS)
¾ HE ALSO FOUND AT SAC PEAK A STRONG CORRELATION BETWEEN CONTRAST AND SEEING
CORRELATION OF
SOLAR SCINTILLATION
&
SOLAR LIMB MOTION
Seykora
CORRELATION OF
SOLAR SCINTILLATION
&
GRANULATION CONTRAST
Rimmele
NOTE: AT SAC PEAK SEEING IS DOMINATED BY BOUNDARY LAYER TURBULENCE
ATMOSPHERIC OPTICS
(using Roddier, Progress in Optics XIX, 283, 1981)
Notations:
σI2 = (ΔIRMS/I)2 = Scintillation Index
r0 = Fried Parameter at 500 nm
ζ = Zenith Distance
Cn2(h) = Refractive Index Structure Constant
σI2 (for Stars) = 19.2*λ-7/6*cos-11/6ζ*,h+5/6*Cn2(h)dh
™ LOOKING AT THE SUN ONE RECEIVES A CONE OF LIGHT ~ 0.01 RADIAN IN WIDTH Ö ONE
AVERAGES THE ATMOSPHERIC EFFECTS OVER AN AREA WHICH INCREASES WITH
INCREASING DISTANCE Ö HIGHER LAYERS CONTRIBUTE LESS TO SCINTILLATION INDEX
σI2 (for Sun) = 0.955x106*cos-2/3ζ*,h-1/3*Cn2(h)dh (independent of λ!)
™ ALSO:
r0-5/3 = 0.060*λ2*cosζ*,Cn2(h)dh (:) FWHMseeing5/3
⇒ σI(Sun)2/FWHM5/3 = const.* ,h-1/3*Cn2(h)dh/ ,Cn2(h)dh
™ THIS RATIO IS DOMINATED BY BOUNDARY LAYER OPTICAL TURBULENCE. WHEN IT
DOMINATES (as it does in daytime) THIS RATIO DOES NOT VARY MUCH WITH TIME
AND LOCATION Ö EXPLAINS SEYKORA RELATION
EARLY “ADVANCED TECHNOLOGY SOLAR TELESCOPE” SITE SURVEY
Used Single Scintillometers Pointed
at Meridional Transit of Sun
Sites Tested:
Big Bear Lake,CA
Lake Heron,NM
La Palma/ORM
Mauna Loa,HI
Sac Peak,NM
“lakeshine”
SHABAR = SHAdow BAnd Ranger
NON-REDUNDANT SOLAR SCINTILLOMETER ARRAY
Correlation of ►
SHABAR pairs
SHABAR Pair
Light Path
DIMM
Yunnan’s Fuxian Hu Seeing Monitor
Correlation
Coefficient
vs Separation
16 cm
2 cm
20 cm
6 cm
4 cm
SHABAR
100 cm
200 cm
S-DIMM PANEL
SHABAR PANELS
CCD IMAGE
OF SLITS
ACROSS
SOLAR LIMB
INTERPRETATION OF THE ATST SHABAR DATA
DEVELOPED BY P. HICKSON, F. HILL, M. COLLADAS & H. SOCAS-NAVARRO
USE: H. Socas-Navarro, J. Beckers, et al. PASP 117, 1296, 2005
CVobs(d)
“missing scintillation”
(due to L0 & time filtering)
constant*CVtheory(h,d)
d=0 mm
h-1/3 curve
d=12mm
d=12mm
¾ Inversion of Equation ⇒ Cn2(h)
¾ Inclusion of DIMM Results (r0)
⇒ ∆s
d=468mm
16 curves corresponding to 16 spacings
¾ Since 10 mm < d < 500 mm
Height Range is Limited to
~ 0.2m< h < 500m
TEST OF SHABAR Cn2(h)
DETERMINATIONS USING
100+ METER DASH TOWER
IN ERIE, COLORADO
NEXT TO AN ATST
SEEING MONITOR
FINAL ATST SITE SURVEY INCLUDED 6 SITES IN USA, MEXICO AND EUROPE
Big Bear, CA
Haleakala, HI
La Palma, Spain
Panguitch Lake (UT)
Sacramento Peak, NM
San Pedro Martir, MX
LAKE SITES
LAND SITES
HEIGHT VARIATION OF Cn2 AND SEEING (r0)
Collados
Socas-Navarro
STATISTICAL RESULTS OF TWO INVERSION PROGRAMS
(full: Collados analysis; dashed: Socas-Navarro analysis)
CONCLUSIONS:
• Place Telescope
at h > 25m
• Haleakala is
best site
• Conclusion based
also on number
of periods with
continuous very
good seeing
THE SCINTILLATION OF
MOON AND PLANETS
™ FULL MOON ONLY (= like Sun)
™ PLANETS AT OPPOSITION ONLY
™ DO NOT INCLUDE SATURN BECAUSE OF ITS RINGS
™ PLANETS: URANUS (dia 3.60 arcsec,; mV = 5.5)
MARS
(dia 17.9 arcsec.; mV = -2.0)
JUPITER (dia 46.9 arcsec.: mV = -2.6)
0 arcsec.
3.6 arcsec.
h+5/6
17.9 arcsec.
46.9 arcsec.
h-1/3
1920 arcsec.
• SCINTILLATION OF MARS IS ALMOST PROPORTIONAL TO THE SEEING
• L0 (Ö “missing scintlillation ∆s”) IS OF NO CONCERN FOR STARS & PLANETS
SUN/
MOON
100
m
1000
m
m
0000
h =1
h=
h=
0m
h=1
STARS
JUPITER
MARS
URANUS
THANK YOU