Temporal Pointing Variations of the Solar Dynamics Observatory’s HMI and AIA Instruments on Subweekly Time Scales
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Achieving subarcsecond co-registration across varying time-lines of multi-wavelength and instrument images is difficult and requires an accurate characterization of the instrument pointing jitter. We investigated the internal pointing errors on daily and yearly time-scales that occur across the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI). Using cross-correlation techniques on the AIA 1700 Å passband and the HMI line-of-sight magnetograms from three years of observational image pairs at approximately three-day intervals, internal pointing errors were quantified. Pointing variations of ± 0.26″ (jitter-limited) and ± 0.50″ in the solar East–West (x) and North–South (y) directions, respectively, were measured. AIA observations of the Venus transit in June 2012 were used to measure existing coalignment offsets in all passbands. We found that the AIA passband pointing variations are 〈ΔX CO〉=1.10″±1.41″ and 〈ΔY CO〉=1.25″±1.24″ when aligned to the HMI nominal image center, referred to here as the CutOut technique. Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that the image-center positions provided by the instrument teams achieve single-pixel accuracy on time scales shorter than their characterization. However, daily AIA passband pointing variations of ≲ 1.18″ indicate that autonomous subarcsecond co-registration is not fully achieved yet.
KeywordsCo-alignment AIA HMI Venus transit
The authors are very grateful for discussions and comments from P. Boerner, and to R. Shine for providing us with extensive AIA pointing data. The authors are very grateful for the referee’s constructive comments and suggestions on this article. This research was supported by the National Aeronautics and Space Administration (NASA) grant NNX-07AT01G. N.B. Orange was also supported by the Florida Space Grant Consortium, a NASA sponsored program administered by the University of Central Florida, grant NNX-10AM01H. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF or NASA.
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