Geostationary Environment Monitoring Spectrometer (GEMS): Long-Term Radiometric Accuracy and Spectral Stability From 4.5 Years of On-Orbit Solar Irradiance Observations

作者：Juseon Bak, Kai Yang, Arno Keppens, Mijeong Kim, Xiong Liu, Jae-Hwan Kim, Jhoon Kim, Myoung‐Hwan Ahn, Heesung Chong, Sungjae Hong, Kyunghwa Lee, Mina Kang, Won‐Jin Lee, Hyunkee Hong · 发表于：IEEE Transactions on Geoscience and Remote Sensing · 年份：2025 · DOI：10.1109/tgrs.2025.3627802 · 被引用次数：2 · 研究领域：Calibration and Measurement Techniques、Atmospheric Ozone and Climate、Optical Polarization and Ellipsometry

The Geostationary Environment Monitoring Spectrometer (GEMS), the first ultraviolet-visible hyperspectral imager in geostationary orbit, has been operating since its launch in February 2020. This paper evaluates and discusses the on-orbit performance of GEMS using 4.5 years of irradiance measurements (300-500 nm), with particular emphasis on the long-term changes in its radiometric accuracy and spectral stability. As part of this assessment, we examine various super-Gaussian forms used for deriving on-orbit slit functions and conclude that applying symmetry constraints to both shape and width parameters enhances fitting stability and accuracy. During the initial phase of operation, the full width at half maximum (FWHM) of the derived slit functions ranged from 0.56 to 0.58 nm across spatial and spectral dimensions. The wavelength shift remains spatially uniform and varies smoothly within ± 0.05 nm, showing a consistent, repeating pattern in 300-400 nm and 400-500 nm. However, over time, instrument degradation has led to pronounced spectral and spatial variations, particularly at shorter wavelengths. Slit widths (FWHM) at the center pixels fluctuate between 0.54 and 0.60 nm, and a “frown-shaped” spatial pattern emerges in the wavelength shift. Radiometric offsets exhibit a steady increase—approximately 5 % per year at shorter wavelengths below 330 nm and 0.2 % above 460 nm. By 2024, irradiance values are up to 35 % lower near 325 nm and about 10 % lower above 460 nm compared t...