QUASAR: QUantum-based Absolute in-SAtellite Radiometric-calibration

The reliability and long-term stability of Earth Observation (EO) data products depend fundamentally on the accurate calibration of optical and infrared detectors. Current spaceborne radiometers, spectrometers, and imaging payloads rely on onboard blackbody sources, sun diffusers, deep space calibration port and ground-based reference targets. Although these techniques are mature, they remain limited by ageing effects and degradation, contamination, spectral non-uniformity, and the absence of true absolute traceability. These limitations impact climate data records, the reliability and stability of the data, the performances and quality of the products, inter-mission consistency, and the ability to meet increasingly stringent scientific and user requirements in domains such as environmental monitoring, atmospheric composition, disaster management, and climate services. The QUASAR concept proposes a quantum-based on-board calibration architecture that derives detector efficiency from fundamental photon pair correlations. By exploiting the absolute properties of quantum states, this approach removes the dependence on external radiometric reference standards and enables intrinsically traceable, self-contained, and highly stable in-flight calibration. The study investigates the feasibility of implementing a compact quantum optical source within EO payloads, with the objective of providing real-time, absolute calibration of Charge-Coupled Device, Complementary Metal-Oxide-Semiconductor, and Single-Photon Avalanche Diode-array detectors across the visible to short-wave infrared spectrum. The work presented assesses QUASAR as an integrated application that links advanced quantum technologies with the operational needs of EO user communities. The study addresses four dimensions essential to end-to-end solution development: 1. Scientific relevance, by identifying EO application sectors where improved calibration stability directly enhances societal and environmental decision-making; 2. Future potential, by quantifying performance improvements relative to current techniques and evaluating benefits for users who depend on long-term climate records and high-precision retrievals; 3. Feasibility, through architectural and engineering analyses that consider mass, power, thermal stability, and optical integration constraints for space deployment; 4. Strategic alignment, by situating the concept within the broader service value chain that supports climate services, environmental monitoring, and policy-driven EO programmes. By introducing an absolute radiometric reference that is independent of ageing and external targets, QUASAR has the potential to reinforce the robustness and societal impact of EO applications that rely on continuous, high-quality and stable data streams. The concept represents a cross-disciplinary pathfinder that bridges quantum technology, space engineering, and user-driven climate services, and offers a promising avenue for future integrated EO systems. The study is conducted as part of an activity funded by the European Space Agency and carried out in collaboration between INRIM, Starion Italia S.p.A., ASTRO S.r.l., and Politecnico di Torino.