Going beyond hardware limitations with advanced stray light calibration for the Metop-3MI space instrument

Space optical instruments play a pivotal role in enhancing our understanding of the universe and our planet, and are crucial in addressing the urgent challenges posed by climate change. In this context, stray light has emerged as a primary performance limitation. Originating from ghost reflections or scattering, it obscures essential details and introduces false information into images. With the demand for increasingly high-performing instruments, mitigation through hardware optimization is becoming insufficient. We are entering an era where future instruments require a stray light correction algorithm to meet user specifications, necessitating extensive on-ground calibration. This paper examines the Metop-3MI Earth observation instrument, which, with wide field of view, broad spectral range, and multi-polarization capabilities, epitomizes the challenges of stray light calibration and correction. A custom calibration apparatus was constructed to evaluate the complex stray light dependence on field-of-view, wavelength, and polarization. Data were processed, and stray light kernels database was derived, which then fed into a specially developed correction algorithm. Applied to the image of an extended scene, it effectively reduces stray light by a remarkable factor of 91. This achievement sets a new standard for low-stray-light instruments and provides a comprehensive case study for future missions.