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Polarization Calibration of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) |
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| Authors: | J Schou J M Borrero A A Norton S Tomczyk D Elmore G L Card |
| Institution: | 1. W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, 94305-4085, USA 2. High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green CG-1, Boulder, CO, 80301, USA 5. Kiepenheuer-Institut für Sonnenphysik, Sch?neckstr. 6, 79104, Freiburg, Germany 3. School of Engineering & Physical Sciences, James Cook University, Townsville, QLD, 4810, Australia 4. National Solar Observatory/Sacramento Peak, 3010 Coronal Loop, Sunspot, NM, 88349, USA |
| Abstract: | As part of the overall ground-based calibration of the Helioseismic and Magnetic Imager (HMI) instrument an extensive set of polarimetric calibrations were performed. This paper describes the polarimetric design of the instrument, the test setup, the polarimetric model, the tests performed, and some results. It is demonstrated that HMI achieves an accuracy of 1% or better on the crosstalks between Q, U, and V and that our model can reproduce the intensities in our calibration sequences to about 0.4%. The amount of depolarization is negligible when the instrument is operated as intended which, combined with the flexibility of the polarimeter design, means that the polarimetric efficiency is excellent. |
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