Validation of an extreme-ultraviolet desaturation technique for the atmospheric imaging assembly on board the solar dynamics observatory using observations from the extreme ultraviolet imager on board solar orbiter

Abstract

High-dynamic-range imaging in the extreme-ultraviolet regime is frequently compromised by detector saturation and charge blooming during intense solar flares, preventing reliable photometry of flare cores. This study presents, for the first time, a direct validation of a sparsity-regularized inverse-diffraction desaturation algorithm applied to saturated images from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory, using contemporaneous short-exposure, unsaturated observations from the Extreme Ultraviolet Imager on Solar Orbiter. The validation exploits a near-radial spacecraft alignment on 2024 March 19, when an M2.1 flare erupted in active region 13615. To obtain coregistered intensity maps, the data were processed with reprojection onto a common helioprojective grid, exposure-time normalization, light-travel-time correction, and field-of-view pointing refinement. Photometric comparisons were performed using peak-based statistics within a rigorously defined region of interest. Results show close morphological agreement and a temporally stable ratio between the desaturated and reference intensities through the impulsive and early decay phases. An early-phase discrepancy is observed and attributed to rapid subexposure evolution, sampling effects, and bandpass/response differences. These findings demonstrate that the desaturation procedure successfully recovers physically meaningful time-dependent core fluxes and, for the first time, provide independent empirical support for the use of desaturated archive frames in quantitative studies of large flares.