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Calibration and Data reduction Strategies

Calibration and Data reduction Strategies. Cormac Purcell & Ned Ladd Mopra Training Weekend May 2005. I Calibration. Measuring Source Intensity. Background Emission (CMB). Source. Atmosphere … t ( Opacity). Electronic Noise. Measuring Source Intensity.

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Calibration and Data reduction Strategies

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  1. Calibration and Data reduction Strategies Cormac Purcell & Ned Ladd Mopra Training Weekend May 2005

  2. I Calibration

  3. Measuring Source Intensity

  4. Background Emission (CMB) Source Atmosphere … t (Opacity) Electronic Noise

  5. Measuring Source Intensity Pon-src = C [ Isrc e-t + J(Tatm)(1-e-t) + Ibg e-t+ IRx ] Source Atmosphere Microwave Background Electronic Noise Poff-src = C [ J(Tatm)(1-e-t) + Ibg e-t+ IRx ] Isrc = (Pon-source – Poff-source) (et/C)

  6. Measuring Source Intensity Tsys Isrc Tsys = Poff-source et/C Tsys is a measure of noise in the whole system. TA* = (Pon-source – Poff-source) Poff-source Poff-source et C = C [ J(Tatm)(1-e-t) + Ibge-t + Irx ] et/C Tsys = J(Tatm)et – J(Tatm) + Ibg + Irxet . . . (1)

  7. Measuring Tsys with a Hot Load Compare blank sky to a known temperature standard: Psky Pload

  8. Compare power from blank sky and known load: Poff-src J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Poff-src Iload + IRx - J(Tatm)(1-e-t) - Ibge-t - IRx = Measuring Tsys with a Hot Load Power measered from blackbody paddle: Pload = C[Iload + Irx]

  9. Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky J(Tatm) e-t - Ibge-t = Measuring Tsys with a Hot Load Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky Iload - J(Tatm)(1-e-t) - Ibge-t = Assume: Tload = Tatm i.e. Iload = J(Tatm)

  10. Tsys J(Tatm)et – J(Tatm) + Ibg + IRxet J(Tatm) - Ibg = Psky Pload – Psky Tsys J(Tatm) - Ibg = Measured Assumed : 300 K & < 1K Measuring Tsys with a Hot Load Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky J(Tatm) e-t - Ibge-t =

  11. What if Tload = Tatm? Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky Iload - J(Tatm)(1-e-t) - Ibge-t = Cannot merge terms.

  12. What if Tload = Tatm? Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky (Iload – J(Tatm)) + J(Tatm)e-t - Ibge-t = J(Tatm)et – J(Tatm) + Ibg + IRxet (Iload – J(Tatm))et + J(Tatm) - Ibg = Tsys (Iload – J(Tatm))et + J(Tatm) - Ibg = Tsys no longer depends on Measurable Quantities

  13. Calibration to TA* scale (Pon-source – Poff-source) Poff-source TA* = Tsys Psky Pload- Psky Tsys= (J(Tload) – Ibg) Assumed 300 K (Ambient temperature) <1 K From CMB

  14. TA* is Not Enough:Calibrating to a Telescope-Independent Scale • TA* scale assumes source emission fills the forward hemisphere • TA* = Tsource only if this is true • In practice, one needs to consider the coupling between the source intensity distribution and the telescope response as a function of angle

  15. Antenna Temperature from an Extended Source Tsource(f) Pb(f) dW TA* = 2p Tsource(f) Pb(f) dW 2p Pb(f) f need to know something about the beam…

  16. 2003 Beam Greyscale: 10% - 100% Contours: 1% - 10%

  17. 2004 Beam Greyscale: 10% - 100% Contours: 1% - 10%

  18. Pb(f)

  19. Extended beam +/- 80’’ Main Beam +/- 40’’

  20. Tsource(f)Pmb(f) dW TA* = hmb 2p Pmb(f) dW 2p Main Beam brightness temperature Tmb = TA*/hmb Main Beam Efficiency, hmb Pmb(f) dW Tsource(f)Pmb(f) dW TA* = 2p 2p Pb(f) dW Pmb(f) dW 2p 2p

  21. Main Beam Brightness Temperature Scale • Tmb = Tsource for a source which fills only the main beam • @Mopra, this means sources with size ~80” • For smaller sources, need to consider beam dilution • i.e., Tmb = <TR> over the main beam • hmb = 0.4 @86 GHz in 2004

  22. Tsource(f)Pxb(f) dW TA* = hxb 2p Pxb(f) dW 2p Extended Beam brightness temperature Txb = TA*/hxb Extended Beam Efficiency, hxb Pxb(f) dW Tsource(f)Pxb(f) dW TA* = 2p 2p Pb(f) dW Pxb(f) dW 2p 2p

  23. Extended Beam Brightness Temperature Scale • Txb = Tsource for a source which fills both the main and extended beams • @Mopra, this means sources with size >150” • hmb ~ 0.6 @86 GHz in 2003

  24. Calibration of Mopra Data • Frequent Tsys measurements • Every 20 minutes in good weather • Always after changing target source •  TA* scale • Knowledge of source size • Choose efficiency based on coupling between source intensity distribution and beam pattern •  Tmb, Txb, or Tsource

  25. II Data Reduction

  26. Reduction Steps • Remove band-pass (off position) • Fit a polynomial to the baseline • Average individual spectra • Scale to required temperature scale • Measure line profiles - e.g. fit with Gaussian

  27. ATNF Single-dish Analysis Package

  28. ATNF Single-dish Analysis Package

  29. ATNF Single-dish Analysis Package

  30. Exporting your data • Export from ASAP • Export as an ASCII text file (e.g. TA* vs V) • Export from SPC • Export as FITS & use perl script to fix headers • Import to CLASS • Read ASCII file & manualy fill headers • Use CFITS to convert from SPC-FITS

  31. Exporting your data Direct export from ASAP to FITS coming soon!

  32. Questions?

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