Spectral performance analysis of the Aeolus Fabry–Pérot and Fizeau interferometers during the first years of operation

Benjamin Witschas,Thomas Flament,Uwe Marksteiner,Oliver Lux,Christian Lemmerz,Oliver Reitebuch,Michael Vaughan,Frederic Fabre,Alain Dabas,Dorit Huber,Fabian Weiler

doi:10.5194/amt-15-1465-2022

Abstract

Abstract. In August 2018, the European Space Agency (ESA) launched the first Doppler wind lidar into space, which has since then been providing continuous profiles of the horizontal line-of-sight wind component at a global scale. Aeolus data have been successfully assimilated into several numerical weather prediction (NWP) models and demonstrated a positive impact on the quality of the weather forecasts. To provide valuable input data for NWP models, a detailed characterization of the Aeolus instrumental performance as well as the realization and minimization of systematic error sources is crucial. In this paper, Aeolus interferometer spectral drifts and their potential as systematic error sources for the aerosol and wind products are investigated by means of instrument spectral registration (ISR) measurements that are performed on a weekly basis. During these measurements, the laser frequency is scanned over a range of 11 GHz in steps of 25 MHz and thus spectrally resolves the transmission curves of the Fizeau interferometer and the Fabry–Pérot interferometers (FPIs) used in Aeolus. Mathematical model functions are derived to analyze the measured transmission curves by means of non-linear fit procedures. The obtained fit parameters are used to draw conclusions about the Aeolus instrumental alignment and potentially ongoing drifts. The introduced instrumental functions and analysis tools may also be applied for upcoming missions using similar spectrometers as for instance EarthCARE (ESA), which is based on the Aeolus FPI design.

Highlights

Since 22 August 2018, the first European spaceborne lidar and the first ever spaceborne Doppler wind lidar, Aeolus, developed by the European Space Agency (ESA), has been circling on its sun-synchronous orbit at about 320 km altitude with a repeat cycle of 7 d (ESA, 2008)
During an instrument spectral registration (ISR) measurement, the laser frequency is scanned over a range of 11 GHz and thereby resolves the entire free spectral range (FSR) of the double-edge Fabry–Pérot
During an ISR measurement, the laser frequency is scanned over a range of 11 GHz to cover one FSR of the Fabry–Pérot interferometers (FPIs) and with that about five FSRs of the Fizeau interferometer

Summary

Introduction

Since 22 August 2018, the first European spaceborne lidar and the first ever spaceborne Doppler wind lidar, Aeolus, developed by the European Space Agency (ESA), has been circling on its sun-synchronous orbit at about 320 km altitude with a repeat cycle of 7 d (ESA, 2008). Aeolus carries a single payload, namely the Atmospheric Laser Doppler Instrument (ALADIN), which provides profiles of the wind component along the instruments’ line-of-sight (LOS) direction on a global scale from the ground up to about 30 km (e.g., ESA, 1999; Stoffelen et al, 2005; Reitebuch, 2012; Kanitz et al, 2019; Reitebuch et al, 2020; Straume et al, 2020). For the use of Aeolus observations in NWP models, a detailed characterization of the data quality as well as the minimization of systematic errors is crucial. Several scientific and technical studies have been performed and published in the addressing the performance of ALADIN and the quality of the Aeolus data products

Methods

Findings

Discussion

Conclusion