gbt performance

20 June 2006 Green BankGBT Performance

GBT Performance

Dana S. Balser

GBT Performance 20 June 2006 Green Bank

Telescope Structure

Surface

Focus

Pointing

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Point Source Calibrators

Condon & Yin (2005)

PCALS 4.0: 7108 sourcesTwo-dimensional rms error < 0.2 arcsec

3 mm pointing calibrators

GBT Performance 20 June 2006 Green Bank

Pointing Model

Cos(E)A SeriesAzimuth E SeriesElevation

Balser et al. (2002)

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Finite Element Model – Gain Elevation Curve

K-band (20 GHZ)

GBT Performance 20 June 2006 Green Bank

Finite Element Model – Sidelobes

O12 EL

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Non-repeatable Errors – Wind

1''

12

2

11

68

2)(

sec16.0)(

smsat

windwind

arcsm

swind

GBT Performance 20 June 2006 Green Bank

Thermal Pointing and Focus Corrections

Constantikes (2003)

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Performance – Blind Pointing

GBT Performance 20 June 2006 Green Bank

Pointing Data Quality – Polarization

arcsec 0.57 0.13- RCP] - [LCP

GBT Performance 20 June 2006 Green Bank

Pointing Data Quality – Direction

arcsec 3.2B] - [F

arcsec 0.89- B] - F[

El

Az

GBT Performance 20 June 2006 Green Bank

Cross-Elevation Uncertainty

arcsec 2.7 Cos(E)]A [

GBT Performance 20 June 2006 Green Bank

Elevation Uncertainty

arcsec 4.8 E][

GBT Performance 20 June 2006 Green Bank

Focus Data Quality – Polarization

mm 0.810.0019- RCP] - [LCP

GBT Performance 20 June 2006 Green Bank

Focus Uncertainty

mm 1.2][ f

GBT Performance 20 June 2006 Green Bank

Performance – Offset Pointing

GBT Performance 20 June 2006 Green Bank

Offset Pointing Uncertainty

arcsec 7.22

GBT Performance 20 June 2006 Green Bank

Offset Focus Uncertainty

mm 2.1

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Power Spectrum

Servo resonance 0.28 Hz

GBT Performance 20 June 2006 Green Bank

Servo Error

GBT Performance 20 June 2006 Green Bank

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 20 June 2006 Green Bank

Surface Improvements – Holography

Traditional Holography(Phase Coherent Holography)

Out-of-Focus Holography(Phase Retrieval Holography)

Maddalena

Nikolic et al. (2006)

GBT Performance 20 June 2006 Green Bank

Zernike Polynomials – Radial Terms

Zernike (1934)Wyant & Creath (1992)

GBT Performance 20 June 2006 Green Bank

Zernike Polynomials – Images

Wyant & Creath (1992)

GBT Performance 20 June 2006 Green Bank

OOF Holography – Gravity

c )Cos( b )Sin( a)(zi

Nikolic et al. (2006)

GBT Performance 20 June 2006 Green Bank

Gain-Elevation Curve

Nikolic et al. (2006)

FEM only

FEM + OOF

GBT Performance 20 June 2006 Green Bank

OOF Holography – Thermal Effects

m300 rms m220 rms

m220 rms

m220 rms

m330 rms