On-Orbit Spectral Calibration of FY-3E/SSIM: Shifts in Asymmetric Spectral Broadening

Solar Fraunhofer lines used for on-orbit wavelength calibration of spaceborne hyperspectral instruments are not universally applicable across all payloads. Existing calibration methods often overlook asymmetric shifts introduced by spectral broadening and lack a unified criterion for standard line selection, which significantly limits cross-comparison of spectral data among different instruments. In this study, we developed a theoretical model of asymmetric broadening and proposed a symmetry-based metric derived from energy integration. Using Kurucz and TSIS-1 HSRS spectra, we verified a strong correlation between asymmetric wavelength shifts and line symmetry. These shifts are jointly influenced by the asymmetric distribution of nearby spectral features within the convolution bandwidth and the instrument’s spectral resolution. After evaluating 22 Fraunhofer lines, we established a line selection guideline with potential applicability to other payloads and applied it to the spectral calibration of FY-3E/SSIM. This work provides key insights into on-orbit wavelength calibration for spaceborne hyperspectral instruments.