POINT-SPREAD FUNCTIONS FOR THE EXTREME-ULTRAVIOLET CHANNELS OFSDO/AIA TELESCOPES

Abstract

We present the stray-light point-spread functions (PSFs) and their inverses we characterized for the Atmospheric Imaging Assembly (AIA) EUV telescopes on board the Solar Dynamics Observatory (SDO) spacecraft. The inverse kernels are approximate inverses under convolution. Convolving the original Level 1 images with them produces images with improved stray-light characteristics. We demonstrate the usefulness of these PSFs by applying them to two specific cases: photometry and differential emission measure (DEM) analysis. The PSFs consist of a narrow Gaussian core, a diffraction component, and a diffuse component represented by the sum of a Gaussian-truncated Lorentzian and a shoulder Gaussian. We determined the diffraction term using the measured geometry of the diffraction pattern identified in flare images and the theoretically computed intensities of the principal maxima of the first few diffraction orders. To determine the diffuse component, we fitted its parameterized model using iterative forward-modeling of the lunar interior in the SDO/AIA images from the 2011 March 4 lunar transit. We find that deconvolution significantly improves the contrast in dark features such as miniature coronal holes, though the effect was marginal in bright features. On a percentage-scattering basis, the PSFs for SDO/AIA are better by a factor of two than that of the EUV telescope on board the Transition Region And Coronal Explorer mission. A preliminary analysis suggests that deconvolution alone does not affect DEM analysis of small coronal loop segments with suitable background subtraction. We include the derived PSFs and their inverses as supplementary digital materials.

The multi-thermal emission in solar active regions

“…4). We corrected for the AIA stray light using the results of Poduval et al (2013). We note that the correction for the stray light is significant (up to 50% changes) for some active regions and enhances the contrast between the loop structures and the background.…”

“…To increase the S/N, we averaged the AIA images over a minute, between 11:40 and 11:41 UT. We corrected for the AIA stray light using the results of Poduval et al (2013) and applied our corrections for the AIA plate scale. We then calculated the predicted radiances in a sample of EIS lines.…”

“…In principle these observations allow the study of the thermal structure of active regions at high spatial resolution. Another significant advance compared to previous instruments is the low stray light, which has been recently assessed by Poduval et al (2013).…”

Non-parametric PSF estimation from celestial transit solar images using blind deconvolution

“…A similar method was used to estimate the PSF of the SWAP instrument on board the PROBA2 satellite (Seaton et al 2013). Finally, Poduval et al (2013) provided a semi-empirical model for the Atmospheric Imaging Assembly (AIA) on board SDO, similar to the one used by DeForest et al (2009) for TRACE. In all these works, the complete set of parameters that were fitted is in the range of 5-11 values, just a few compared to the resolution of the PSF (millions of pixels).…”

“…In addition to building a parametric model of the PSF using the specifications of the instruments, some works (DeForest et al 2009;Shearer et al 2012;Poduval et al 2013) have used the information from a celestial transit to help in inferring the PSF of a given instrument. A celestial transit, shown in Figure 1, is an astronomical event where the Moon or a planet moves across the disk of the sun, hiding a part of it, as seen from the telescope.…”