PhD in Physics, Discipline Sciences de la Matière, du Rayonnement et de l'Environnement
Thesis defended on 19th December 2018
Laboratoire d'Optique Atmosphérique (LOA)
Advanced aerosol characterization using sun/sky photometer and multi-wavelength Mie-Raman lidar measurements
There are two objectives in this study : (i) aerosols characterization using multi-wavelength Mie-Raman lidar and (ii) the retrieval of aerosol properties through lidar and sun/sky pho- tometer joint measurements. The measurements investigated were recorded in two obser- vation sites : Lille (France) and M’bour, (Senegal). The measurements in M’bour were conducted in the SHADOW2 (Study of SaHAran Dust Over West Africa) campaign, in the framework of Labex CaPPA.
Aerosol characterization presented in this study concerns Saharan dust in M’Bour, long- range transported dust and Canadian smoke, as well as dust-smoke mixtures. Dust proper- ties during the dry season and the transition period from dry to wet season, are characteri- zed with lidar measurements in M’Bour. We found the contrast of dust properties during the two periods, explained by the intrusion of marine aerosols. Long-range transported Saharan dust in Lille showed distinct properties compared to the observations in M’Bour, indicating the impact of the transport process. Transported Canadian smoke plumes were detected at high altitude over Lille and exhibit surprisingly high depolarization ratios, which is possibly caused by the smoke ageing process. Additionally, dust-smoke mix- tures measured in M’Bour and Lille point out the differences of aerosol origins.
In the second part of this study, lidar volume linear depolarization ratio has been inclu- ded in the aerosol retrieval algorithm GARRLiC/GRASP. Sensitivity tests are performed to test the performance of GARRLiC/GRASP under different aerosol content, with dif- ferent sphere fraction and with different error levels of molecular depolarization ratio and calibration coefficient. Then GARRLiC/GRASP is applied to real sun/sky photometer and lidar measurements and the retrievals are compared with results from independent methods for verification. The comparison shows that GARRLiC/GRASP retrievals are very consistent with the results from independent methods, but tend to produce 10% lo- wer dust particle depolarization ratio compared to the lidar measurements.
Over all, our results are relevant to the European scientific community since GARR- LiC/GRASP is being implemented in the ACTRIS data and service center. This work will benefit to the evaluation of future European space missions.
Key words : Aerosol characterization ; remote sensing ; inversion algorithm
Thesis supervisor :
Philippe GOLOUB, LOA
Thesis co-supervisor :
Oleg Dubovik, LOA
Lucas Alados Arboledas
Financing: Agence spatiale européenne (ESA)