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Zero Point Correction

Zero Point Correction. Basic Steps - I. For a given site on a given day: Create a magnetic flat field from the east & west calibration images. Using the magnetic flat, create a “reference magnetogram” from the calibration solar image and the observations near the calibration sequence

llewellyn-timothy
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Zero Point Correction

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  1. Zero Point Correction

  2. Basic Steps - I • For a given site on a given day: • Create a magnetic flat field from the east & west calibration images. • Using the magnetic flat, create a “reference magnetogram” from the calibration solar image and the observations near the calibration sequence • Create 10-min averages of the magnetograms during the day. • Register, rotate and remap the averages and reference to a common scale and time

  3. Basic Steps II • Subtract the reference from each 10-min average. • Fit the differences with Zernicke polynomials. • Fit the time series of Zernicke coefficients with 24-hr and 12-hr sinusoids. • Smooth the harmonic fit coefficients over several days. • These final coefficients can be used to compute a correction for the magnetogram at any time

  4. Zernickes

  5. Time Series of Zernicke Coefficients

  6. Before processing, zero point varies across image by about 5-10 G. After processing, variation is about 1 G at best Not good enough, want 0.1-0.3 G Seeing noise is a significant problem How well does it work?

  7. Questions • Will a software correction be needed after the new modulator is installed? • If so, will the current method be adequate? • If not, how can it be improved? • How can it be tested?

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