A.A. Norton1, T.L. Duvall Jr.1,2, J. Schou2, R.S. Bogart1, Junwei Zhao1, M.C. Rabello-Soares1, P.J. Levens1, J.T. Hoeksema1, C.S. Baldner1
1. W.W. Hansen Experimental Physics Laboratory, Solar Physics, Stanford University, Stanford, CA 94301-4085, USA
2. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
We report a point spread function (PSF) and deconvolution procedure to remove stray light from data acquired by HMI[1,2]. In 2018, the HMI team began providing full-disk, stray-light-corrected data daily. Intensity, Doppler, magnetogram, and vector magnetic field data are provided. The deconvolution uses a Richardson-Lucy algorithm and takes less than one second per full-disk image. The results, on average, show decreases in umbral continuum intensity, a doubling of the granulation intensity contrast, increases in the total field strength, most notably in plage by ∼1.4–2.5 the original value, and a partial correction for the convective blueshift. Local helioseismology analyses using corrected data yield results that are consistent with those from uncorrected data, with only negligible differences, except in sunspot regions.
Pre-launch calibration observations, post-launch Venus transit and lunar transit data were used to develop the PSF and evaluate how well it reproduced the observed scattering. The PSF is a Lorenztian convolved with an Airy function. The deconvolution uses a Richardson-Lucy algorithm[3] and takes less than one second per full-disk image.
Figure 1. A 150 x 150 pixel field of view containing a sunspot (NOAA 13110) from 2022.09.28 19 UT is shown comparing the original (left), deconvolved (middle), and difference (right) for the 720-second Ic data (top), field strength (middle) and Doppler velocity (bottom). Colored contours indicate the fraction of the quiet-Sun continuum intensity. Differences are shown as a % difference for Ic (original minus the deconvolved divided by the original), in units of Gauss for B, and units of m s-1 for the Dopplergram. Grayscale minimum and maximum values are the same for the left and middle plots.
Figure 2. Location of plage are denoted as blue points in a 700 x 700 pixel Ic image (left) with a corresponding field strength image, saturated at a low value of 400 Mx cm-2, to show location of plage (middle). A scatter plot of VFISV solutions for the total field strength, B, of original and deconvolved data is shown (right). The slope of the red dashed line, m=1.56, represents a fit to the deconvolved and original plage field strengths. Plage are defined as locations where the deconvolved field strength is greater than or equal to 400 Mx cm-2, the intensity is greater than 0.9 of the mean intensity, and it is located at least 100 pixels away from the center of the umbra (otherwise penumbral fields will be included). The field strengths for penumbra and umbra are less affected than those of plage, as evident in the field strengths in the range of 2000-3000 seen in the scatter plot with a solid red line showing unity.
The new data are found in JSOC with names similar to the original but with the qualifying term ’_dcon’ or ’_dconS’ appended, denoting whether the deconvolution was applied to the filtergrams or Stokes images[4]. For example, one would search in JSOC for hmi.M_45s_dcon to find stray light corrected hmi.M_45s data, or hmi.sharp_cea_720s_dconS for stray light corrected hmi.sharp_cea_720s data. The HMI team recommends using the corrected data for improved visual clarity, more accurate irradiance reconstruction, better co-alignment with high-resolution data, reduced errors in tracking algorithms, and improved magnetic field strengths. For more details about the stray light correction, please read the paper here.
[1] Norton et al. 2026,
[2] Scherrer, P. H., Schou, J., Bush, R. I., et al. 2012, SoPh, 275, https://doi.org/10.1007/s11207-011-9834-2
[3] Richardson, W. H. 1972,
[4] Couvidat et al. 2016, Sol. Phys., 291, 1887, https://doi.org/10.1007/s11207-016-0957-3