Articles | Volume 9, issue 10
Atmos. Meas. Tech., 9, 4935–4953, 2016

Special issue: EARLINET, the European Aerosol Research Lidar Network

Atmos. Meas. Tech., 9, 4935–4953, 2016

Research article 07 Oct 2016

Research article | 07 Oct 2016

Assessment of lidar depolarization uncertainty by means of a polarimetric lidar simulator

Juan Antonio Bravo-Aranda1,2,3, Livio Belegante4, Volker Freudenthaler5, Lucas Alados-Arboledas1,2, Doina Nicolae4, María José Granados-Muñoz1,2, Juan Luis Guerrero-Rascado1,2, Aldo Amodeo6, Giusseppe D'Amico6, Ronny Engelmann7, Gelsomina Pappalardo6, Panos Kokkalis8, Rodanthy Mamouri9, Alex Papayannis8, Francisco Navas-Guzmán1,2,a, Francisco José Olmo1,2, Ulla Wandinger7, Francesco Amato6, and Martial Haeffelin3 Juan Antonio Bravo-Aranda et al.
  • 1Andalusian Institute for Earth System Research (IISTA-CEAMA), Granada, Spain
  • 2Dpt. Applied Physics, University of Granada, Granada, Spain
  • 3Institute Pierre-Simon Laplace, CNRS-Ecole Polytechnique, Paris, France
  • 4National Institute of Research & Development for Optoelectronics – INOE 2000, Magurele, Ilfov, Romania
  • 5Ludwig-Maximilians-Universität Meteorologisches Institut, München, Germany
  • 6Consiglio Nazionale delle Ricerche Istituto di Metodologie per l'Analisi Ambientale I.M.A.A. – C.N.R., Potenza, Italy
  • 7Leibniz Institute for Tropospheric Research (TROPOS), Permoserstr. 15, 04318 Leipzig, Germany
  • 8Laser Remote Sensing Unit, National Technical University of Athens, Physics Dept., 15780 Zografou, Greece
  • 9Department of Civil Engineering and Geomatics, Cyprus University Of Technology, Lemesos, Cyprus
  • anow at: Institute of Applied Physics (IAP), University of Bern, Bern, Switzerland

Abstract. Lidar depolarization measurements distinguish between spherical and non-spherical aerosol particles based on the change of the polarization state between the emitted and received signal. The particle shape information in combination with other aerosol optical properties allows the characterization of different aerosol types and the retrieval of aerosol particle microphysical properties. Regarding the microphysical inversions, the lidar depolarization technique is becoming a key method since particle shape information can be used by algorithms based on spheres and spheroids, optimizing the retrieval procedure. Thus, the identification of the depolarization error sources and the quantification of their effects are crucial. This work presents a new tool to assess the systematic error of the volume linear depolarization ratio (δ), combining the Stokes–Müller formalism and the complete sampling of the error space using the lidar model presented in Freudenthaler (2016a). This tool is applied to a synthetic lidar system and to several EARLINET lidars with depolarization capabilities at 355 or 532 nm. The lidar systems show relative errors of δ larger than 100 % for δ values around molecular linear depolarization ratios (∼ 0.004 and up to ∼  10 % for δ = 0.45). However, one system shows only relative errors of 25 and 0.22 % for δ = 0.004 and δ = 0.45, respectively, and gives an example of how a proper identification and reduction of the main error sources can drastically reduce the systematic errors of δ. In this regard, we provide some indications of how to reduce the systematic errors.

Short summary
This work analyses the lidar polarizing sensitivity by means of the Stokes–Müller formalism and provides a new tool to quantify the systematic error of the volume linear depolarization ration (δ) using the Monte Carlo technique. Results evidence the importance of the lidar polarizing effects which can lead to systematic errors larger than 100 %. Additionally, we demonstrate that a proper lidar characterization helps to reduce the uncertainty.