07 Jul 2022
07 Jul 2022
Status: a revised version of this preprint is currently under review for the journal AMT.

First assessment of Aeolus L2A particle backscatter coefficient retrievals in the Eastern Mediterranean

Antonis Gkikas1, Anna Gialitaki1,5,6, Ioannis Binietoglou1, Eleni Marinou1, Maria Tsichla1, Nikolaos Siomos1, Peristera Paschou1,5, Anna Kampouri1,7, Kalliopi Artemis Voudouri1,5, Emmanouil Proestakis1, Maria Mylonaki2, Christina-Anna Papanikolaou2, Konstantinos Michailidis5, Holger Baars3, Anne Grete Straume4, Dimitris Balis5, Alexandros Papayannis2, Tomasso Parrinello8, and Vassilis Amiridis1 Antonis Gkikas et al.
  • 1Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Athens, Greece
  • 2Laser Remote Sensing Unit, Department of Physics, National and Technical University of Athens, Athens, Greece
  • 3Leibniz-Institut für Troposphärenforschung e.V., Leipzig, Germany
  • 4European Space Agency (ESA/ESTEC), Noordwijk, Netherlands
  • 5Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
  • 6Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom
  • 7Department of Meteorology and Climatology, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
  • 8European Space Agency (ESA/ESRIN), Frascati, Italy

Abstract. Since 2018, the Aeolus satellite of the European Space Agency (ESA) acquires wind HLOS (horizontal line-of-sight) profiles throughout the troposphere and up to the lower stratosphere, filling a critical gap of the Global Observing System (GOS). Aeolus, carrying ALADIN, the first UV HSRL Doppler lidar ever placed in space, along with wind HLOS profiles provides also vertically resolved optical properties of particulates (aerosols, hydrometeors). The present study focuses on the assessment of Aeolus L2A particulate backscatter coefficient, retrieved by the Standard Correct Algorithm (SCA), in the Eastern Mediterranean, a region hosting a variety of aerosol species. Ground-based retrievals acquired by lidar instruments operating in Athens (capital of Greece), Thessaloniki (north Greece) and Antikythera (southwest Greece) serve as reference. All lidar stations provide routine measurements to the PANACEA (PANhellenic infrastructure for Atmospheric Composition and climatE chAnge) network. A set of ancillary data including sunphotometric observations (AERONET), reanalysis products (CAMS, MERRA-2), satellite observations (MSG-SEVIRI, MODIS-Aqua) and backward trajectories (FLEXPART) are utilized towards an optimum characterization of the probed atmospheric conditions under the absence of a classification scheme in Aeolus profiles. First, emphasis is given on the assessment of Aeolus L2A backscatter coefficient under different aerosol scenarios over Antikythera island. Due to the misdetection of the cross-polar component of the backscattered lidar signal, Aeolus underestimates backscatter by up to 33 % when non-spherical mineral particles are recorded (10th July 2019). A very good performance is revealed on 3rd July 2019, when homogeneous loads of fine spherical particles are confined below 4 km. The level of agreement between spaceborne and ground-based retrievals varies with altitude when aerosol layers, composed of particles of different origin, are stratified (8th July 2020, 5th August 2020). According to the statistical assessment analysis for 46 identified cases, it is revealed a poor-to-moderate performance for the unfiltered (aerosols plus clouds) Aeolus profiles which improves substantially when cloud contaminated profiles are excluded from the collocated sample. This positive tendency is evident at both Aeolus vertical scales (regular, 24 bins and mid-bin, 23 bins) and it is justified by the drastic reduction of the bias and root-mean-square-error scores. In vertical, Aeolus performance downgrades at the lowermost bins (attributed to either the surface reflectance or the increased noise levels for the Aeolus retrievals and to the overlap issues for the ground-based profiles). Among the three PANACEA stations, the best agreement is found at the remote site of Antikythera with respect to the urban sites of Athens and Thessaloniki. Finally, all key Cal/Val aspects necessary for future relevant studies, the recommendations for a possible Aeolus follow-on mission and an overview of the ongoing related activities are thoroughly discussed.

Antonis Gkikas et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-205', Anonymous Referee #1, 01 Aug 2022
  • RC2: 'Comment on amt-2022-205', Anonymous Referee #2, 08 Aug 2022
  • RC3: 'Comment on amt-2022-205', Anonymous Referee #3, 09 Aug 2022

Antonis Gkikas et al.

Antonis Gkikas et al.


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Short summary
We perform an assessment analysis of Aeolus L2A backscatter coefficient retrievals against reference observations acquired at three Greek lidar stations (Athens, Thessaloniki, Antikythera) of the PANACEA network. Overall, 46 cases are analyzed whereas emphasis is given of specific aerosol scenarios in the vicinity of the Antikythera island (SW Greece). All key Cal/Val aspects and recommendations as well as the ongoing related activities are thoroughly discussed.