Nasti, Libera (2009) Development of a Multiparametric Lidar with the depolarization sensor. [Tesi di dottorato] (Unpublished)

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Item Type: Tesi di dottorato
Uncontrolled Keywords: Lidar, depolarization sensor, atmospheric aerosols
Date Deposited: 10 Mar 2010 13:08
Last Modified: 30 Apr 2014 19:40
URI: http://www.fedoa.unina.it/id/eprint/4146

Abstract

The topic of this work was the design, the realization and the calibration of the depolarization sensor added in the Napoli Lidar (Light Detection and Ranging) system. In addition a complete rebuilding of the receiving system was operated, and a new characterization of all the components of the apparatus was done. From the advent of Lidar technology in 1970 the study of the composition of the atmosphere gets a speed up. Lidar is an active sensor that sends into the atmosphere a short laser pulse and measures the elastic and Raman shifted optical backscattered power from molecules and aerosols. From the delay of the received pulse, the position of the scattering elements is obtained. Analyzing the backscattered radiation some important optical properties of the atmospheric aerosols can be derived: backscattering and extinction coefficients, position and altitude of the layers, colour index and so on. In this context, a depolarization-sensitive Lidar can help to characterize the particle’s shape. The discrimination of the shape of the aerosols is very important, for example to distinguish the phase of the clouds (ice-clouds are strongly asymmetric scatterers while low clouds are made by spherical water’s drops) and the type of aerosols (Saharan dust is constituted by non-spherical particles while urban aerosols by little spherical particles). The depolarization measurements can be performed by using a linearly polarized laser source and a hardware configuration of the receiving system including two channels detecting simultaneously the backscattered radiation in the parallel and orthogonal direction with respect to the laser beam. The total depolarization ratio, due both to molecular and aerosol contributions, is simply the calibrated ratio of the orthogonal signal to the parallel one. So, a key question to obtain high quality depolarization measurements is performing a good calibration of the Lidar system. In this work different calibration techniques were analyzed by simulating lidar signals in different atmospheric conditions. In Napoli the sensor was realized and then calibrated while in Potenza the depolarization sensor was only calibrated. These two systems were calibrated with different techniques, due to different apparatus conditions. My scientific activity was spent for the most in the Atomic and Laser Applications Laboratory in Physics Department of University Federico II of Napoli. A period of three months was also spent in C.N.R.-I.S.A.C.(Istituto di Scienze Atmosferiche e Climatiche), in Bologna, where some theoretical models about the atmospheric dynamic were developed. Two months period was also spent in C.N.R.-I.M.A.A. (Istituto di Metodologie per l’Analisi Ambientale- Tito Scalo-Potenza), working under the supervision of Dr. Gelsomina Pappalardo.

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