The wind mission Aeolus of the European Space Agency was a seminal achievement in Earth observation and space laser technology. During its nearly five-year lifetime, the space-borne Doppler wind lidar instrument ALADIN onboard the Aeolus satellite employed two switchable ultraviolet laser transmitters to measure atmospheric wind profiles with global coverage, contributing to improving the accuracy of numerical weather prediction. Despite the excellent performance of the nominal and redundant laser which was optimized during the mission through thermal adjustments, the atmospheric return signal levels declined between 2019 and 2022 due to decreasing transmission of the optics between the redundant laser and the telescope. The root cause analysis of the signal loss was supported by the Pierre Auger Observatory in Argentina whose fluorescence detector registered the ultraviolet laser pulses emitted from the instrument in space, thereby offering an independent measurement of the laser energy.
Lux et al. (Thu,) studied this question.