Ground observations of a space laser for the assessment of its in-orbit performance

TL;DR

This paper demonstrates how ground-based observations of a space laser can assess and improve the in-orbit performance of the laser instrument, with implications for space laser calibration and cosmic-ray observatories.

Contribution

It introduces a novel method using ground-based fluorescence detectors to evaluate and calibrate space laser performance over time.

Findings

Laser energy at the instrument exit was estimated for multiple days.

Ground observations improved laser beam ground track accuracy.

The method offers a new way to monitor space laser health and calibration.

Abstract

The wind mission Aeolus of the European Space Agency was a groundbreaking achievement for Earth observation. Between 2018 and 2023, the space-borne lidar instrument ALADIN onboard the Aeolus satellite measured atmospheric wind profiles with global coverage which contributed to improving the accuracy of numerical weather prediction. The precision of the wind observations, however, declined over the course of the mission due to a progressive loss of the atmospheric backscatter signal. The analysis of the root cause 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 estimation of the laser energy at the exit of the instrument for several days in 2019, 2020 and 2021. The reconstruction of the laser beam not only allowed for an independent assessment of the Aeolus performance, but also helped to improve the accuracy in the determination of the laser beam's ground track on single pulse level. The results presented in this paper set a precedent for the monitoring of space lasers by ground-based telescopes and open new possibilities for the calibration of cosmic-ray observatories.