Towards a demonstrator setup for a wide-field-of-view visible to near-infrared camera aiming to characterize the solar radiation reflected by the Earth

Climate change monitoring is still a major challenge, which is currently typically addressed using radiometers monitoring the radiative fluxes at the top of the atmosphere. To improve the current state-of-the-art monitoring instruments, we pursue the development of novel space instrumentation, combining a radiometer with two additional imagers, improving the spatial resolution to a few kilometers allowing scene identification, while enabling a spectral distinction between the reflected solar radiation (RSR) using a visible to near-infrared (400 – 1100 nm) camera, and the Earth’s emitted thermal radiation using a thermal infrared (8 – 14 µm) camera. In this paper, we present a novel camera design optimized towards RSR monitoring, while targeting a compact design and minimizing the number of aspheric components. More specifically, our optimized imaging design shows a wide field of view (138°) enabling to observe the Earth from limb to limb, a compact volume fitting within 1 CubeSat Unit (1U), a wide spectral range (400 – 900 nm) to retrieve the RSR with a certainty of more than 95%, a spatial resolution better than 5 km at nadir, and a close to diffraction-limited performance. After optimization towards the nominal design, possible design alternatives are considered and discussed, enabling a cost-efficient design choice. Following, the mechanical and optical design tolerances are evaluated using a statistical Monte Carlo analysis, indicating a robust and tolerant design that can be manufactured using ultra-precision diamond tooling. Finally, stray-light analysis was performed enabling evaluation of ghost reflection and evaluating the necessity of an anti-reflection coating. Consequently, we can conclude our proposed imaging designs show a promising performance optimized towards Earth observation, paving the way to an improved climate change monitoring.