CCD detector performance of the space-borne Doppler wind lidar ALADIN during the Aeolus mission

Kurzfassung

The Aeolus mission, launched by the European Space Agency in August 2018, was a landmark in Earth observation by providing global wind profiles in near-real time using the first Doppler wind lidar in space: the Atmospheric Laser Doppler Instrument (ALADIN). Despite challenges such as systematic errors affecting data quality at the beginning of the mission, Aeolus surpassed its planned lifetime of three years and proved invaluable for weather prediction and scientific research until its conclusion in July 2023. A permanent challenge throughout the mission involved mitigating the impact of hot pixels on the ALADIN charge-coupled device (CCD) detectors on the wind data. The related dark current anomalies, which manifested as random telegraph signal noise and sporadic shifts in median dark current signal, necessitated the development of dedicated calibration techniques to minimize the induced systematic wind speed errors. The regular dark current calibrations of up to eight times per day yielded a comprehensive dataset that was used to categorize the hot pixels according to their characteristics and to derive statistical parameters that are of relevance for the reprocessing of the Aeolus data products. Following the end of the operational mission in April 2023, a series of specialized in-orbit tests, referred to as end-of-life (EOL) activities, provided valuable insights into the temperature dependence of the dark currents, shedding light on potential root causes of the hot pixels. Additionally, the EOL tests revealed other detector anomalies that had caused significant wind biases in certain altitudes following strong cosmic ray events in 2022. This work summarizes the performance of the ALADIN detectors during the Aeolus mission, with a focus on hot pixel characterization and mitigation strategies. Furthermore, it highlights findings from the EOL activities that are relevant for future space lidar missions and other satellite missions using CCD detectors.