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Brewer characterization challenges (mostly questions)

Brewer characterization challenges (mostly questions). Volodya Savastiouk EUBREWNET, Manchester, UK September 26, 2013. Why do we care?. Any data are only as good as is our understanding of what the instrument is doing

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Brewer characterization challenges (mostly questions)

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  1. Brewer characterization challenges(mostly questions) Volodya Savastiouk EUBREWNET, Manchester, UK September 26, 2013

  2. Why do we care? Any data are only as good as is our understanding of what the instrument is doing Brewer is a complex instrument with many electronic, mechanical and optical elements that interact in complicated ways

  3. What is involved in Brewer characterization: partial list (assuming it is working!) • Voltages – must be just right • High Voltage on PMT • HG and SL voltages/currents • Run/Stop – can we claim counting is working? • Dead Time – is the system linear? • Temperature Coefficients • Dispersion – micrometer vs diff.grating positions • Neutral density filter attenuations (spectral) • Focusing (fore-optics, monochromator) • HG and Sun Scan – how are these related?

  4. Voltages • PMT high voltage • How do we select it? • What are the implications of getting it wrong? • Lamps’ voltages • Is there a/the correct voltage for SL?

  5. Run/Stop and Dead Time • Again, what are the implications of RS being out of specs? • Why the direct-sun observations sometimes suggest a different Dead Time value than the one calculated from the DT test on the internal lamp?

  6. Dispersion and ND filters • Which lamps/lines to use? • Does it make a difference? • What about repeatability of both tests? • How do we calculate ozone and SO2 absorption coefficients? • Which xsecs set is right and why? • We need to include the sun and ozone in calculations of absorption coefficients

  7. Focusing • Do we get in trouble if we have the fore-optics out of focus? • What happens to HG tests if the monochromator is out of focus in the UV?

  8. HG, Sun Scans and focusing, again • If the monochromator is out of focus HG reference may change with time and or with bulbs • The sun doesn’t change spectrally (less than HG anyway) so Sun Scans are a more reliable wavelength check

  9. Moving forward • Standard Operating Procedures • Many of the stated issues are mostly inconsistencies and EUBREWNET can and should help by (continue) developing and implementing consistent procedures for every Brewer characterization test • Studies • Dispersion • Dead Time • Neutral Density Filters

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