Green Bank Telescope Performance
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Transcript of Green Bank Telescope Performance
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July 2007 Pune, NCRAGBT Performance
Green Bank Telescope Performance
Dana S. Balser
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GBT Performance July 2007 Pune, NCRA
Telescope Structure
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GBT Performance July 2007 Pune, NCRA
Unblocked Aperture
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GBT Performance July 2007 Pune, NCRA
Frequency Coverage
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GBT Performance July 2007 Pune, NCRA
Telescope Control
Surface
Focus
Pointing
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GBT Performance July 2007 Pune, NCRA
Pointing Requirements
2
2El
2Az
22
2
2
GHZ
arcsec 740
2ln4exp)(
f
g
Condon (2003)
20.0 10%)( Usable
14.0 5%)( Good
s
s
f
f
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GBT Performance July 2007 Pune, NCRA
Focus Requirements
2/8/)95.0( Usable
4/16/)99.0( Good
4
Axial 2ln4exp2
asa
asa
a
a
sa
yg
yg
yg
Srikanth (1990)Condon (2003)
5.03.17
mm 3.2 mm 7 :band-Q
mm/3.7Scale Plate
3/16/)99.0( Good
6
Lateral 2ln4exp
"
"
2
f
x
xg
xg
s
lsl
l
l
sl
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GBT Performance July 2007 Pune, NCRA
Surface Requirements
Ruze (1966)Condon (2003)
37.04/:Usable
54.016/ :Good
area.primary geometric theis A
.efficiency aperture theis
.atmosphere for the corrected re temperatuantenna theis T
constant. sBoltzmann' isk
density.flux theisS
A
kT2S
error. surface rms theis
surface. for the efficiency aperture theis
4exp
g
a
'A
ga
'A
s
2
s
s
s
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GBT Performance July 2007 Pune, NCRA
Repeatable Errors – Pointing
• Telescope misalignments:• Azimuth track tilt• Horizontal collimation• Elevation axle collimation• Encoder offsets
• Gravity: assume linear elastic structure
Cos(E)d Sin(E)b Cos(A)d Sin(A)c d E
E)Sin(A)Sin(a E)Cos(A)Sin(b
Cos(E)d Sin(E)bd Cos(E)A
0,10,11,01,00,0
1,11,1
0,10,10,0
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GBT Performance July 2007 Pune, NCRA
Repeatable Errors – Focus
• Gravity: assume linear elastic structure
Sin(E) C Cos(E) B A Z
Sin(E) C Cos(E) B A Y
Sin(E) C Cos(E) B A X
zzz
yyy
xxx
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GBT Performance July 2007 Pune, NCRA
Repeatable Errors – Surface
• Gravity: • Homologous design (almost)• Photogrammetry (50.3 deg) Zero-point • Finite Element Model (FEM)• Best Fit Parabola (BFP) Active Surface: 2004 Panels
2209 Actuators
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GBT Performance July 2007 Pune, NCRA
Point Source Calibrators
Condon & Yin (2005)
PCALS 4.0: 7108 sourcesTwo-dimensional rms error < 0.2 arcsec
3 mm pointing calibrators
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GBT Performance July 2007 Pune, NCRA
Pointing Model
Cos(E)A SeriesAzimuth E SeriesElevation
Balser et al. (2002)
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GBT Performance July 2007 Pune, NCRA
Focus Model
Axial Focus
mm Sin(E) 21.86 - Cos(E) 11.18 9.56 Z
mm Sin(E) 9.96 Cos(E) 183.74 148.39- Y
mm Sin(E) 25.55 - Cos(E) 301.98 - 212.55 X
Ghigo et al. (2001)
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GBT Performance July 2007 Pune, NCRA
Finite Element Model – Gain Elevation Curve
K-band (20 GHZ)
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GBT Performance July 2007 Pune, NCRA
Finite Element Model – Sidelobes
O12 EL
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GBT Performance July 2007 Pune, NCRA
Non-repeatable Errors – Thermal
GHz 30at 3 mm 30
2/8/)95.0( Usable
GHz 30 offrequency aat 3 mm 30
GHz 3 offrequency aat /3 mm 03
asa yg
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GBT Performance July 2007 Pune, NCRA
Non-repeatable Errors – Wind
0.20 f 10%) s
( Usable
GHz 20at 0.22 f 1sm6sat''8
wind1
2)wind(2
arcsec
2
1sm
s16.0)wind(
1
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GBT Performance July 2007 Pune, NCRA
Thermal Pointing and Focus Corrections
Constantikes (2003)
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GBT Performance July 2007 Pune, NCRA
Data Collection and Quality
Gaussian Fits (Az, El, Focus)
Polarization (LCP – RCP)
Direction (Forward – Backward)
Jack Scan
All-sky ObservationsSingle Source Track
Up-Down at Night GravityNCP Source Temperature
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GBT Performance July 2007 Pune, NCRA
Thermal Model – Focus
Constantikes (2003)
Term Coefficient Min-Max Significance Parameter
M1 1.086 13.1 14.3 SR-PriM2 -0.697 6.2 -4.3 VFA-PriM3 3.981 15.6 62.0 HFAM4 -7.326 0.9 -6.8 BUS V1M5 -0.688 12.1 -8.3 BUS V2M6 -2.576 12.1 -31.2 BUS FM7 -180.630 0.0 0.0 Offset
M8 66.189 .7 43.1 sin term
M9 196.949 0.6 110.8 cos term
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GBT Performance July 2007 Pune, NCRA
Thermal Model – Azimuth
Constantikes (2003)
Term Coefficient Min-Max Significance Parameter
M1 5.5862 4.0 22.4 Alidade M2 -8.0331 2.7 21.3 HFAM3 -1.6289 2.4 3.8 BUSM4 1.3683 2.0 2.8 VFAM5 3.4124 0.0 0.0 CA, d(0,0)M6 1.3223 0.7 1.0 NPAE, b(0,1)M7 3.5152 0.9 3.0 IA, d(0,1)M8 -2.4960 1.9 4.8 AW, b(1,1)M9 -1.3360 1.8 2.5 AN, a(1,1)
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GBT Performance July 2007 Pune, NCRA
Thermal Model – Elevation
Constantikes (2003)
Term Coefficient Min-Max Significance Parameter
M1 -4.6455 1.2 -5.3 BUSM2 1.7830 15.6 -27.8 HFAM3 4.4488 5.9 26.4 VFAM4 -8.4477 1.6 -14.0 AlidadeM5 62.2218 0.0 +0.000 -IE,d(0,0)M6 -55.8624 0.7 -62.792 HZCZ,b(0,1)M7 -22.8268 0.9 -38.216 HZSZ,d(0,1)M8 2.4960 2.0 +2.169 -AW,c(1,0)M9 -1.3360 2.0 -1.750 AN,d(1,0)
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GBT Performance July 2007 Pune, NCRA
Performance – Blind Pointing
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GBT Performance July 2007 Pune, NCRA
Pointing Data Quality – Polarization
arcsec 0.57 0.13- RCP] - [LCP
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GBT Performance July 2007 Pune, NCRA
Pointing Data Quality – Direction
arcsec 3.2B] - [F
arcsec 0.89- B] - F[
El
Az
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GBT Performance July 2007 Pune, NCRA
Cross-Elevation Uncertainty
arcsec 2.7 Cos(E)]A [
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GBT Performance July 2007 Pune, NCRA
Elevation Uncertainty
arcsec 4.8 E][
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GBT Performance July 2007 Pune, NCRA
Focus Data Quality – Polarization
mm 0.810.0019- RCP] - [LCP
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GBT Performance July 2007 Pune, NCRA
Focus Uncertainty
mm 1.2][ f
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GBT Performance July 2007 Pune, NCRA
Performance – Offset Pointing
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GBT Performance July 2007 Pune, NCRA
Offset Pointing Uncertainty
arcsec 7.22
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GBT Performance July 2007 Pune, NCRA
Offset Focus Uncertainty
mm 2.1
mm 2.1
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GBT Performance July 2007 Pune, NCRA
Performance – Tracking
arcsec 2.12 )/'10,/'2(,
)5,1(),(
)58,290(),(
mmt
El
t
Az
ElAz
ElAz
)m/'7.11,m/'8.10(t
El,
t
Az
)9.3,6.3()El,Az(
)37,99()El Az,(
Half-power in Azimuth Half-power in Elevation
)m/'4.11,m/'0.12(t
El,
t
Az
)8.3,0.4()El,Az(
)43,105()El Az,(
arcsec 2.12
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GBT Performance July 2007 Pune, NCRA
Power Spectrum
Servo resonance 0.28 Hz
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GBT Performance July 2007 Pune, NCRA
Servo Error
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GBT Performance July 2007 Pune, NCRA
Performance – Summary
mm 2.5 focus)(
arcsec 5pointing)(1
mm 1.5 focus)(
arcsec 7.2pointing)(2
Benign Conditions: (1) Exclude 10:00 18:00 (2) Wind < 3.0 m/s
Blind Pointing: (1 point/focus)
Offset Pointing: (90 min)
Continuous Tracking: (30 min)
arcsec 12
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GBT Performance July 2007 Pune, NCRA
Surface Improvements – Holography
Traditional Holography(Phase Coherent Holography)
Out-of-Focus Holography(Phase Retrieval Holography)
Maddalena
Nikolic et al. (2006)
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GBT Performance July 2007 Pune, NCRA
Zernike Polynomials
Zernike (1934)Maeda (2003)
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GBT Performance July 2007 Pune, NCRA
OOF Holography – Gravity
c
Cos(E) b
Sin(E) a)E(zi
Nikolic et al. (2006)
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GBT Performance July 2007 Pune, NCRA
Gain-Elevation Curve
Nikolic et al. (2006)
FEM only
FEM + OOF
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GBT Performance July 2007 Pune, NCRA
OOF Holography – Thermal Effects
m300 rms m220 rms
m220 rms
m220 rms
m330 rms
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GBT Performance July 2007 Pune, NCRA
Summary Surface Performance