Katcha Winther is a PhD student at the Measurement and Instrumentation division at DTU Space, the National Space Institute.
Here, she is working on the juLIET (Lunar Imaging Earthshine Telescope) instrument from design to final integration. juLIET will be the first space-based earthshine telescope.
The goal of the mission is to measure earthshine reflected from the Moon to estimate the Earth’s albedo, i.e., the ratio of sunlight which is reflected back into space contra the light which is absorbed by Earth – a key parameter in the energy balance equations of our planet’s climate.
Similarly to how moonlight is sunlight reflected of the lunar surface, the reverse – earthlight – illuminates the lunar night. This light, re-reflected back to Earth, can be seen from Earth as earthshine.
The apparent albedo of Earth is proportional to the ratio in intensities of earthshine and moonlight. If the same sensor measures both, common errors like calibration drift, often affecting visual light satellite instruments, cancel out.
However, due to the additional light path, earthshine is several orders of magnitude dimmer than moonlight. Measuring both intensities with a sufficient precision, despite the high dynamic range of the signals, pose the main technological challenge of the mission.
juLIET is a collaboration with DMI (Danish Meteorological Institute) and IRS (Institute of Space Systems) at the University of Stuttgart responsible for the satellite ROMEO (Research and Observation in Medium Earth Orbit), on which juLIET is the primary scientific payload. The project is partially funded by ESA, the European Space Agency, and launch is planned in the end of 2025.
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