Green Bank Telescope Performance
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Transcript of Green Bank Telescope Performance
July 2007 Pune, NCRAGBT Performance
Green Bank Telescope Performance
Dana S. Balser
GBT Performance July 2007 Pune, NCRA
Telescope Structure
GBT Performance July 2007 Pune, NCRA
Unblocked Aperture
GBT Performance July 2007 Pune, NCRA
Frequency Coverage
GBT Performance July 2007 Pune, NCRA
Telescope Control
Surface
Focus
Pointing
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
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
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
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
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
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
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
GBT Performance July 2007 Pune, NCRA
Pointing Model
Cos(E)A SeriesAzimuth E SeriesElevation
Balser et al. (2002)
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)
GBT Performance July 2007 Pune, NCRA
Finite Element Model – Gain Elevation Curve
K-band (20 GHZ)
GBT Performance July 2007 Pune, NCRA
Finite Element Model – Sidelobes
O12 EL
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
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
GBT Performance July 2007 Pune, NCRA
Thermal Pointing and Focus Corrections
Constantikes (2003)
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
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
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)
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)
GBT Performance July 2007 Pune, NCRA
Performance – Blind Pointing
GBT Performance July 2007 Pune, NCRA
Pointing Data Quality – Polarization
arcsec 0.57 0.13- RCP] - [LCP
GBT Performance July 2007 Pune, NCRA
Pointing Data Quality – Direction
arcsec 3.2B] - [F
arcsec 0.89- B] - F[
El
Az
GBT Performance July 2007 Pune, NCRA
Cross-Elevation Uncertainty
arcsec 2.7 Cos(E)]A [
GBT Performance July 2007 Pune, NCRA
Elevation Uncertainty
arcsec 4.8 E][
GBT Performance July 2007 Pune, NCRA
Focus Data Quality – Polarization
mm 0.810.0019- RCP] - [LCP
GBT Performance July 2007 Pune, NCRA
Focus Uncertainty
mm 1.2][ f
GBT Performance July 2007 Pune, NCRA
Performance – Offset Pointing
GBT Performance July 2007 Pune, NCRA
Offset Pointing Uncertainty
arcsec 7.22
GBT Performance July 2007 Pune, NCRA
Offset Focus Uncertainty
mm 2.1
mm 2.1
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
GBT Performance July 2007 Pune, NCRA
Power Spectrum
Servo resonance 0.28 Hz
GBT Performance July 2007 Pune, NCRA
Servo Error
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
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)
GBT Performance July 2007 Pune, NCRA
Zernike Polynomials
Zernike (1934)Maeda (2003)
GBT Performance July 2007 Pune, NCRA
OOF Holography – Gravity
c
Cos(E) b
Sin(E) a)E(zi
Nikolic et al. (2006)
GBT Performance July 2007 Pune, NCRA
Gain-Elevation Curve
Nikolic et al. (2006)
FEM only
FEM + OOF
GBT Performance July 2007 Pune, NCRA
OOF Holography – Thermal Effects
m300 rms m220 rms
m220 rms
m220 rms
m330 rms
GBT Performance July 2007 Pune, NCRA
Summary Surface Performance