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Current GBT Performance. Systematic Focus Errors. Axial Focus Offset: air temperature versus elevation. Gravitational & Temperature Focus Effects. Temperature Effect. Gravitational Effect. Measure focus over short time period. NCP source 0117+8928. Systematic Pointing Errors.

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Presentation Transcript
systematic focus errors
Systematic Focus Errors

Axial Focus Offset: air temperature versus elevation

gravitational temperature focus effects
Gravitational & Temperature Focus Effects

Temperature Effect

Gravitational Effect

Measure focus over short time period

NCP source 0117+8928

plan of attack
Plan of Attack
  • Rationalize data acquisition
  • Rationalize data analysis
  • Implement temperature sensor system
  • Concentrate efforts on pointing and focus
  • Characterize performance with X-band (8 -10 GHz)
data quality
Data Quality

Gaussian Fits (Az, El, Focus)

Polarization (LCP – RCP)

Direction (Forward – Backward)

Jack Scan

data quality pointing lcp rcp1
Data Quality: Pointing (LCP – RCP)

Flux (9 GHz) > 0.08 Jy

RMS < 2.5 arcsec < 0.03 HPBW

data quality focus lcp rcp
Data Quality: Focus (LCP – RCP)

Flux (9 GHz) > 0.08 Jy

RMS < 3.8 mm << focus beamwidth

observational strategy
Observational Strategy
  • NCP source to probe temperature effects
  • Up-down sources at night to probe gravity effects
  • All-sky for a combination
initial results
Initial Results
  • All-sky (Az, El) pointing
    • Removed systematic pointing residuals
  • Simultaneous fits to gravity and temperature
    • Separate two effects
    • Refine focus and pointing models
current performance
Current Performance
  • Model:
    • Simultaneous solution to temperature and gravity effects
  • Datasets:
    • All-sky pointing run (2003 Nov 20)
    • Half-power tracking (2003 Nov 20)
  • Metrics
    • Blind pointing
    • Offset pointing
    • Continuous Tracking
current performance no temperature corrections
Current Performance: (NO temperature corrections)

Benign Conditions: (1) Exclude 10:00  18:00

(2) Wind < 2.5 m/s

Blind Pointing:

(1 point/focus)

Offset Pointing:

(90 min)

Continuous Tracking:

(30 min)

blind pointing 2 d rms
Blind Pointing: 2-D RMS

Raw Residuals

One PEAK at the start of

the evening

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