Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory
| Autor: | Philip H. Scherrer, R. S. Bogart, Sebastien Couvidat, Yijin Liu, J. T. Hoeksema, T. L. Duvall, Jesper Schou, R. I. Bush, Aimee A. Norton |
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| Rok vydání: | 2016 |
| Předmět: |
Physics
Photosphere Orbital speed 010504 meteorology & atmospheric sciences Spacecraft Pixel business.industry Astrophysics::Instrumentation and Methods for Astrophysics FOS: Physical sciences Astronomy and Astrophysics Observable Polarization (waves) 01 natural sciences Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Physics::Space Physics 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics Helioseismology business 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) 0105 earth and related environmental sciences Physical quantity Remote sensing |
| Zdroj: | Solar Physics. 291:1887-1938 |
| ISSN: | 1573-093X 0038-0938 |
| DOI: | 10.1007/s11207-016-0957-3 |
| Popis: | NASA's Solar Dynamics Observatory (SDO) was launched 11 February 2010 with 3 instruments on board, including the Helioseismic and Magnetic Imager (HMI). Since beginning normal operations on 1 May 2010, HMI has observed the Sun's entire visible disk almost continuously. HMI collects sequences of polarized filtergrams taken at a fixed cadence with two 4096 x 4096 cameras from which are computed arcsecond-resolution maps of photospheric observables: the line-of-sight (LoS) velocity and magnetic field, continuum intensity, line width, line depth, and the Stokes polarization parameters, I Q U V, at 6 wavelengths. Two processing pipelines implemented at the SDO Joint Science Operations Center (JSOC) at Stanford University compute observables from calibrated Level-1 filtergrams. One generates LoS quantities every 45s, and the other, primarily for the vector magnetic field, computes averages on a 720s cadence. Corrections are made for static and temporally changing CCD characteristics, bad pixels, image alignment and distortion, polarization irregularities, filter-element uncertainty and non-uniformity, as well as Sun-spacecraft velocity. This report explains issues affecting the resulting physical quantities, describes the impact of regular updates to the instrument calibration, and shows how the computations are optimized for actual HMI observations. During the 5 years of the SDO prime mission, regular calibration sequences have been used to regularly improve and update the instrument calibration and to monitor instrument changes. The instrument more than satisfies the original specifications for data quality and continuity. The procedures described here still have significant room for improvement. The most significant remaining systematic errors are associated with the spacecraft orbital velocity. Accepted for publication in Solar Physics |
| Databáze: | OpenAIRE |
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