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Systematic Analysis of Gravitational and Temperature Effects on Pointing and Focus Accuracy

This study presents a detailed examination of systematic pointing errors associated with gravitational and temperature variations. By rationalizing data acquisition and analysis, and implementing advanced temperature sensors, we aim to refine pointing and focus models. The investigation focuses on using X-band (8-10 GHz) and Ku-band (14 GHz) data to characterize performance and assess the impacts of temperature and gravity. We employ observational strategies such as all-sky pointing and up-down sources to differentiate between these effects, ultimately enhancing data quality and accuracy in observations.

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Systematic Analysis of Gravitational and Temperature Effects on Pointing and Focus Accuracy

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  1. Current GBT Performance

  2. Systematic Focus Errors Axial Focus Offset: air temperature versus elevation

  3. Gravitational & Temperature Focus Effects Temperature Effect Gravitational Effect Measure focus over short time period NCP source 0117+8928

  4. Systematic Pointing Errors

  5. 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)

  6. Data Quality Gaussian Fits (Az, El, Focus) Polarization (LCP – RCP) Direction (Forward – Backward) Jack Scan

  7. Observational Strategy • NCP source to probe temperature effects • Up-down sources at night to probe gravity effects • All-sky for a combination

  8. 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

  9. 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

  10. Blind Pointing: Azimuth

  11. Blind Pointing: Elevation

  12. Blind Focus

  13. Offset Pointing: Azimuth and Elevation

  14. Offset Focus

  15. Tracking: Ku-band (14 GHz) El half-power track

  16. 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)

  17. Supplemental Material

  18. Data Quality: Pointing (LCP – RCP)

  19. Data Quality: Pointing (LCP – RCP) Flux (9 GHz) > 0.08 Jy RMS < 2.5 arcsec < 0.03 HPBW

  20. Data Quality: Focus (LCP – RCP) Flux (9 GHz) > 0.08 Jy RMS < 3.8 mm << focus beamwidth

  21. Data Quality: Pointing (F – B)

  22. Data Quality: Wind

  23. Blind Focus

  24. Blind Pointing: residuals versus (A, Z)

  25. Blind Pointing: residuals versus time

  26. Blind Pointing: 2-D RMS Raw Residuals One PEAK at the start of the evening

  27. Blind Pointing: Azimuth

  28. Blind Pointing: Elevation

  29. Blind Focus

  30. Tracking: Ku-band (14 GHz) El half-power track

  31. Tracking: Ku-band (14 GHz) El half-power track

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