Preprints
https://doi.org/10.5194/amt-2021-74
https://doi.org/10.5194/amt-2021-74

  11 Mar 2021

11 Mar 2021

Review status: this preprint is currently under review for the journal AMT.

ALADIN laser frequency stability and its impact on the Aeolus wind error

Oliver Lux1, Christian Lemmerz1, Fabian Weiler1, Thomas Kanitz2, Denny Wernham2, Gonçalo Rodrigues2, Andrew Hyslop3, Olivier Lecrenier4, Phil McGoldrick5, Frédéric Fabre6, Paolo Bravetti7, Tommaso Parrinello8, and Oliver Reitebuch1 Oliver Lux et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, 82234 Oberpfaffenhofen, Germany
  • 2European Space Agency, European Space Research and Technology Centre, Noordwijk, 2201 AZ, The Netherlands
  • 3Vitrociset (a Leonardo company), for ESA, Noordwijk, 2201 DK, The Netherlands
  • 4Airbus Defence and Space (Toulouse), Rue des Cosmonautes, 31400 Toulouse, France
  • 5Formerly Airbus Defence and Space (Stevenage), Gunnels Wood Rd, Stevenage SG1 2AS, United Kingdom
  • 6Les Myriades SAS, Consultancy for Optical Systems, 2 Rue Temponières, 31000 Toulouse
  • 7Airbus Italia S.p.A., Via dei Luxardo, 22-24, 00156 Rome, Italy
  • 8European Space Agency, European Space Research Institute, 00044 Frascati RM, Italy

Abstract. The acquisition of atmospheric wind profiles on a global scale was realized by the launch of the Aeolus satellite, carrying the unique Atmospheric LAser Doppler INstrument (ALADIN), the first Doppler wind lidar in space. One major component of ALADIN is its high-power, ultraviolet (UV) laser transmitter which is based on an injection-seeded, frequency-tripled Nd:YAG laser and fulfills a set of demanding requirements in terms of pulse energy, pulse length, repetition rate as well as spatial and spectral beam properties. In particular, the frequency stability of the laser emission is an essential parameter which determines the performance of the lidar instrument, as the Doppler frequency shifts to be detected are on the order of 108 smaller than the frequency of the emitted UV light. This article reports the assessment of the ALADIN laser frequency stability and its influence on the quality of the Aeolus wind data. Excellent frequency stability with pulse-to-pulse variations of about 10 MHz (root mean square) is evident for over more than two years of operations in space despite the permanent occurrence of short periods with significantly enhanced frequency noise (> 30 MHz). The latter were found to coincide with specific rotation speeds of the satellite's reaction wheels, suggesting that the root cause are micro-vibrations that deteriorate the laser stability on time scales of a few tens of seconds. Analysis of the Aeolus wind error with respect to ECMWF model winds shows that the temporally degraded frequency stability of the ALADIN laser transmitter has only minor influence on the wind data quality on a global scale, which is primarily due to the small percentage of wind measurements for which the frequency fluctuations are considerably enhanced. Hence, although the Mie wind bias is increased by 0.3 m·s−1 at times when the frequency stability is worse than 20 MHz, the small contribution of 4 % from all wind results renders this effect insignificant (< 0.1 m·s−1) when all winds are considered. The impact on the Rayleigh wind bias is negligible even at high frequency noise. Similar results are demonstrated for the apparent speed of the ground returns that are measured with the Mie and Rayleigh channel of the ALADIN receiver. Here, the application of a frequency stability threshold that sorts out wind observations with variations larger than 20 MHz changes the accuracy of the Mie and Rayleigh ground velocities by less than 0.15 m·s−1.

Oliver Lux et al.

Status: open (until 06 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-74', Weibiao Chen, 23 Mar 2021 reply

Oliver Lux et al.

Oliver Lux et al.

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Short summary
The work assesses the frequency stability of the laser transmitters on-board Aeolus and discusses its influence on the quality of the global wind data. Excellent frequency stability of the space lasers is evident, although enhanced frequency noise occurs at certain locations along the orbit due to micro-vibrations that are introduced by the satellite’s reaction wheels. The study elaborates on this finding and investigates the extent to which the enhanced frequency noise increases the wind error.