Impact of source-monochromator spectral coupling on absolute radiance calibration of spectrometers

Abstract High-precision absolute radiometric calibration is essential for establishing a rigorous metrological traceability system. In monochromator-based calibration chains, the nonlinear spectral coupling between the slit function and the relative spectral distribution of the light source is a critical factor limiting accuracy, yet quantitative assessments remain scarce. To address this, we deduce an equivalent analytical model based on a second-order Taylor series expansion to explicitly reveal the error propagation laws of this bandwidth coupling effect. For rigorous validation, a high-precision absolute calibration system was established using a high-brightness broadband source and an integrating sphere to fully overfill the spectrometer’s field of view. Cross-validation was performed with a combined standard uncertainty of 0.95% ( k = 1). Experimental results are in high agreement with the theoretical analysis: within the 775–805 nm range, the absolute calibration deviation introduced by the finite bandwidth is less than 0.8%. Crucially, this deviation is fully bounded within the total uncertainty limit of the system. This study provides a systematic analysis of the complex spectral coupling mechanism, offering a universal metrological framework for error compensation and solid theoretical support for bandwidth optimization in space radiometric benchmark missions like LIBRA.