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Polarization Calibration of HMI

Polarization Calibration of HMI. A. Norton, J. Schou, D. Elmore, J. Borrero, S. Tomczyk, G. Card + High Altitude Observatory National Center for Atmospheric Research. Polarization Modulation Schemes. Mod A - 4 observations mix linear & circular (80 sec) I Q U V

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Polarization Calibration of HMI

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  1. Polarization Calibration of HMI • A. Norton, J. Schou, D. Elmore, • J. Borrero, S. Tomczyk, G. Card + • High Altitude Observatory • National Center for Atmospheric Research

  2. Polarization Modulation Schemes Mod A - 4 observations mix linear & circular (80 sec) I Q U V I Q U V Mod C - 6 obs separate linear & circular I±Q, I±U, I±V (120 sec) Can correct for velocity during Mod C.

  3. Polarization Calibration Unit (PCU)G. Card, D. Elmore, S. Tomczyk, K. Streander + Linear Polarizer & a 1/4 Waveplate: *Moved in/out of beam (1.25  resolution) *Rotate optics (0.001° resolution) Inputs fixed states of polarization into HMI for calibration purposes

  4. PCU HMI Tel HMI Polarizer Sout Sin Lin 1/4 Pol WP 1/2 1/4 1/2 Lin WP WP WP Pol HMI Tel Ret (,) 17 Unknowns in optical path: 3 - Input light - Slamp= ([1.0], [q], [u], [v]) 4 - PCU - transmissions, retardation error and mount error of WP 2 - HMI tel - retardation and angle 6 - HMI Polarizer - mount errors and retardation errors for WPs, 2 - CCD - gain, bias

  5. Calculating theT-Matrix & Polarimeter Response Matrix • Calibration sequences selected to constrain unknowns: With PCU elements in/out of beam and at various angles, step through a variety of HMI waveplate orientations. Short sequence - 69 exposures, includes Mod A Long sequence - 140 exposures, includes Mod C. • Forward model light path. • Use least squares fitting routine to solve for unknowns. • Combine for Telescope matrix & Polarimeter Response Matrix.

  6. Monte Carlo Simulations - Photon Noise Calibration requirement are that uncertainties in [XT] < 0.1%

  7. Calibration in Progress Polarization data taken Feb 9-10 With PCU in beam. Work in progress. Please check HAO website for updates http://web.hao.ucar.edu/hmi 1st magnetogram 2/7/06 courtesy of J. Schou

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