Lionel Clermont, an engineer at the Centre Spatial de Liège (CSL/ULiège), has just been awarded prestigious funding from the European Research Council (ERC). His project, called nGHOST, aims to push the boundaries of space imaging by developing new methods to study and correct stray light that interferes with optical instruments. Ultimately, his work will make space telescopes and cameras more accurate and reliable, paving the way for unprecedented scientific discoveries.
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n the constantly evolving field of space instrumentation, scientists are striving to design instruments capable of capturing the universe with ever-greater clarity. But for the most demanding applications, stray light—unwanted light reaching the detector through uncontrolled paths—remains a major limiting factor. Ghost reflections, scattering or diffraction degrade resolution and introduce artefacts that can compromise the success of a mission. In Earth observation, for example, it directly affects radiometric accuracy.
The reduction of this stray light must be integrated from the design stage, via the opto-mechanical architecture and the choice of materials, and then validated by ground characterisation. However, current methods are struggling to meet the growing demands of new-generation instruments. "Several missions have revealed unexpected stray light phenomena once in orbit," explains Lionel Clermont, an engineer at the Liège Space Centre. "Reducing these risks is essential to enable the emergence of new instruments and new scientific discoveries."
Illustration of a stray light effect in a camera. Instead of observing a star as a bright spot on a dark background, various artefacts appear on the image, skewing its interpretation. | © Université de Liège/L. Clermont
With more than ten years of experience working with the European Space Agency (ESA), Lionel Clermont led the stray light correction for the 3MI instrument, recently launched aboard MetOp-SG-A1. He has also pioneered time-of-flight stray light characterisation, an innovative method that discriminates stray components according to their optical path length. This approach, applied to several missions such as ERO (Mars exploration) and FLEX (Earth observation), has paved the way for a more detailed understanding of stray light phenomena.
With his ERC nGHOST project, Lionel Clermont aims to push the boundaries of this method. His research will focus on the development of advanced analysis and processing tools capable of systematically identifying defects in an optical system, whether it be a large space telescope or a compact camera.
Thanks to unprecedented sensitivity that can distinguish extremely weak light signals while supporting sources up to a million billion billion times more intense (dynamic range of 10-15), and digital approaches such as machine learning and automatic , his goal is to design correction algorithms capable of improving current performance by two to three orders of magnitude.
Beyond space telescopes, the benefits of this ERC project will find multiple applications in other fields: commercial cameras, microscopes and even smartphones. Ultimately, the goal is to make the invisible visible and enable new scientific discoveries.
See also : A revolutionary method for drastically reducing stray light on space telescopes.
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