Sannino, Alessia (2017) Atmospheric Particles properties retrieval in China-Italy Aerosol Multi-wavelength Polarization Lidar Experiment (AMPLE) Systems. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Resource language: English
Title: Atmospheric Particles properties retrieval in China-Italy Aerosol Multi-wavelength Polarization Lidar Experiment (AMPLE) Systems
Date: 10 April 2017
Number of Pages: 112
Institution: Università degli Studi di Napoli Federico II
Department: Fisica
Dottorato: Fisica
Ciclo di dottorato: 29
Coordinatore del Corso di dottorato:
Spinelli, NicolaUNSPECIFIED
Boselli, AntonellaUNSPECIFIED
Date: 10 April 2017
Number of Pages: 112
Keywords: lidar, inversion, aerosols, desert dust, China, volcanic ash, Etna, AMPLE
Settori scientifico-disciplinari del MIUR: Area 02 - Scienze fisiche > FIS/01 - Fisica sperimentale
Date Deposited: 03 May 2017 15:20
Last Modified: 08 Mar 2018 11:14

Collection description

The Aerosol atmospheric particles give the major contribution to the uncertainties in the knowledge of the atmospheric processes and the radiation balance of the Earth. They play a strong role in the dynamics of the climate change and, at least, in the human health and safety. In fact the transport of huge mass of desert dust or volcanic ash related to eruption, but also still the air pollution in the high industrialized area of our planet, can have several consequences in the human cycles and can hinder the normal human activities as happen in some big city of the China and India, or also in the airports, when the presence of volcanic ash poses serious problems related to the flight safety. However, the great importance that have these particles, is not accompanied by a good knowledge of their properties, due to the vastness of their nature. At present there is a great interest in advancing ever more precise studies on these atmospheric components. In particular, in order to study the climate change, weather forecast and environmental pollution associated with fine particles, volcanic ashes transport information on aerosol sources and synoptic scale measurements (possibly with a time series perspective) are hence necessaries. A performing way to investigate the atmospheric particles is obtained by measuring of the properties of the light scattering and absorption that these particles produced when they interact with the light. This way is known as remote sensing technique. Several instruments are based on this technique but most of them perform measures on the integrated air column and are not able to give spatially resolved information. Conversely, the LIDAR (Light detection and ranging) technique is presently considered an ideal system for the investigation of the atmospheric particles being able to perform measurement in 4D (space and time) with high spatial and time resolution and high sounding range distance. A lidar system can be arranged in different configurations, making it sensible to specific optical interactions and allowing to obtain different levels of knowledge of the aerosol properties. Whatever the configuration, it is always possible to schematize a lidar as basically consisting of a transmitter and a receiver: short laser pulses are sent into the atmosphere and a telescope collects the backscatter photons; these are spectrally analyzed in order to obtain aerosol optical and microphysical information. If the required information are the microphysical properties of the particles a lidar based on single wavelength elastic is not enough, because it allows to know only a limited number of properties. More complex lidar configurations are then required to retrieve information about the shape and the thermodynamic phase of the particles. The present work deals with the problem of the aerosol characterization by using is new LIDAR system designed and developed in the frame of the AMPLE (Aerosol Multi-wavelength Polarization Lidar Experiment) project by the National Interuniversity Consortium for the Physical Sciences of Matter, CNISM, Unit of Napoli in the framework of two scientific cooperation programs with Istituto Nazionale di Geofisica e Vulcanologia, INGV, Section of Catania, (Italy) and the Beijing Research Institute for Telemetry, BRIT, (People's Republic of China). The AMPLE lidar represents a very innovation with respect to standard high performance atmospheric lidars, thanks to the relatively high repetition rate laser source, fast single photon counting, angular scanning and, for the first time, the depolarization ratio measurements at two wavelengths (355 nm and 532 nm). In this contest, as part of my personal PhD work, several data campaigns have been done in different sites (Dunhuang, Catania, Napoli, Beijing, Lijiang) with the AMPLE lidars and the data collected in two of these campaigns have been analyzed. A first observation is related to the data collected from fresh volcanic ash produced by the Strombolian Etna volcano eruption, occurred on 16th of December 2013. During the observed event, the AMPLE lidar was located close the active crater of mount Etna in order to characterize for the first time the fresh volcanic ash, in terms of aerosol backscatter, extinction, lidar ratio profiles, aerosol depolarization ratio and ash concentration. The second important observed phenomena is related to the campaign which took place in Dunhuang, a huge area close to the Gobi desert in China. During this campaign a strong dust event has been recorded, allowing for the first time to study the properties of dust at source and not after long travels in the atmosphere with consequent mixing with local aerosol. The properties are studied in terms of backscatter coefficients, their ratio at two different wavelengths (the Colour Index), ratio of backscattering to extinction coefficient (Lidar Ratio), and for the first time, the linear depolarization at two wavelengths. These works on data analysis are accompanied to another substantial modelling part inherent a new method for the retrieval of optical and micro-physical properties of the particles from lidar measurements of particles optical properties. In fact, unfortunately, also the best performing lidars are able to give a set of particles optical parameters constituted by the values of the extinction coefficient at two wavelengths and the backscattering coefficient at three wavelengths. These data are related in a complex way to the concentration, chemical-physical and geometrical particles properties. Until now there is no stable way to obtain, by lidar data a direct measurements of the microphysical parameters, since these properties are in complicated relationships in the formulation of the optical lidar products. Adding to this, the retrieval of the extinction parameter presents several critical points, it produces instable solution and some a-priori assumption are needed. For the modeling part of my thesis I worked on two new methods for the retrieval respectively of the optical and the microphysical parameters. The first part of this work has been done in collaboration with MIDA (Methods for Image and Data Analysis) group at the Dipartimento di Matematica, Università di Genova and ALA (Advanced Lidar Applications) srl; It consisted of the development of a new method for the inversion of the single Raman equation (related to atmospheric Raman process), to find a stable solution for the extinction parameter. In this frame we have proposed and tested a new discrete and iterative solution based on the well known EM (Expectation-Maximization) method. The second part of the modelling work has been carried out within a cooperation program between MIDA, CNR-SPIN groups and ALA srl, the work represents an important point in the lidar applications. In fact, the target is to obtain information about size, density and refractive index of aerosol particles and their spatial profiles, from a single lidar instrument able to provide at least measurements of 3 backscattering and 2 extinction coefficients.


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