Dr. Thierry G. Elias Profile

Dr. Thierry G. Elias

Researcher/Climate Change-Air Quality at Hygeos

SPIE Involvement:

Author

Publications (5)

Proceedings Article | 1 November 2012 Paper

Preliminary results of the PreViBOSS project: description of the fog life cycle by ground-based and satellite observation

Thierry Elias, Dominique Jolivet, Jean-Charles Dupont, Martial Haeffelin, Frédéric Burnet

Proceedings Volume 8534, 853406 (2012) https://doi.org/10.1117/12.974709

KEYWORDS: Fiber optic gyroscopes, Visibility through fog, Visibility, Clouds, Magnesium, Atmospheric particles, Particles, Mass attenuation coefficient, Refractive index, Aerosols

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The instrument set-up designed by the PreViBOSS project for the ParisFog field campaign is suitable to sound microphysical properties of droplets and interstitial aerosols during developed fog in a semi-urban environment. Developed fog is defined as LWC < 7 mg m^-3 and the temperature vertical gradient over 30 m, ΔT, smaller than 0.04 K/m. Visibility averaged over November 2011 is 385±340 m (with rare values larger than 1000 m), and month average of LWC is 60±60 mg m^-3. The droplet effective radius decreases from 14 to 4 μm when the number concentration increases from less than 10 to 220 cm^-3. Particle extinction coefficient is computed by Mie theory applied on size distribution observed during developed fog in ambient conditions by both PALAS WELAS and DMT FM100. Comparison with particle extinction coefficient directly measured by the Degreanne DF20 visibilimeter demonstrates satisfying agreement, within combined uncertainties. Ratio of computed over measured particle extinction coefficient is 1.15±0.35. Visibility smaller than 1000 m at 3 m above ground level is observed not only during developed fog but also during shallow fog, which presents a significant vertical gradient, as ΔT > 0.4 K/m. In this case, LWC is highly variable and may be observed below 7 mg m^-3. The consequent month average of LWC is 30±80 mg m^-3. The optical counters miss large droplets significantly contributing to extinction in shallow fogs. Consequently, it is not possible to reproduce with satisfaction the particle extinction coefficient in shallow fog. Fog type may be distinguished by association of groundbased visibilimeter and MSG/SEVIRI. When clear-sky is given by EUMETSAT/NWCSAF cloud type product while visibility is observed smaller than 1000 m at SIRTA, in 75% cases a shallow fog occurs, and in other cases, horizontal heterogeneity characterises the developed fog within the SIRTA pixel, as during the dissipation phase. Moreover, consistently, low and very low clouds are mostly detected by the satellite product when developed fog is observed by ground-based instrumentation.

Proceedings Article | 30 November 2004 Paper

Aerosol extinction and absorption in Évora, Portugal, during the European 2003 summer heat wave

Thierry Elias, Ana Silva, Maria Figueira, Nuno Belo, Sergio Pereira, Paola Formenti, Gunter Helas

Proceedings Volume 5571, (2004) https://doi.org/10.1117/12.566579

KEYWORDS: Aerosols, Scattering, Atmospheric particles, Absorption, Ocean optics, Clouds, Optical testing, Radiometry, Particles, Optical properties

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Proceedings Article | 16 February 2004 Paper

Correction of the ground-based measurements of radiance by the surface contribution for a better estimate of the aerosol radiative forcing

Thierry Elias, Ana Silva

Proceedings Volume 5235, (2004) https://doi.org/10.1117/12.514226

KEYWORDS: Aerosols, Sun, Scattering, Refractive index, Atmospheric modeling, Radiative transfer, Atmospheric particles, Reflection, Vegetation, Atmospheric optics

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