First results of the "Earth Radiation Budget and Clouds" operational algorithm

International audienceThe POLDER instrument is devoted to global observations of the solar radiation reflected by the Earth-atmosphere system. Algorithms of the "Earth Radiation Budget and Clouds" processing line implemented at the French Space Center are applied to ADEOS-POLDER data. First results on derived cloud properties are presented from POLDER level 2 data of 10 November 1996 and level 3 products of June 1997. A good correlation is observed between the POLDER cloud detection algorithm and the Dynamical Clustering Method applied to METEOSAT data. The multidirectional capability of POLDER appears useful to check schemes of cloud optical thickness retrieval. As expected, a water droplet model is suitable for liquid water clouds and inadequate for ice clouds. That indirectly validates the algorithm of cloud phase recognition. An apparent pressure is derived from O2-absorption measurements and a Rayleigh cloud pressure from polarization observations. For overcast conditions, the apparent pressure is larger (by more than 100 hPa) than the Rayleigh pressure chiefly due to the photon penetration effect. For partly cloudy conditions, it can be larger or weaker depending on the surface reflectivity. Preliminary comparisons between POLDER and ISCCP monthly mean products outline some differences resulting in part from the original characteristics of POLDE

Intercomparison between aerosol optical properties by a PREDE skyradiometer and CIMEL sunphotometer over Beijing, China

International audienceThis study compares the aerosol optical and physical properties simultaneously measured by a SKYNET PREDE skyradiometer and AERONET/PHOTONS CIMEL sunphotometer at a location in Beijing, China. Aerosol optical properties (AOP) including the Aerosol Optical Depth (AOD), Angstrom exponent (a), volume size distribution, single scattering albedo (?) and the complex refractive index were compared. The difference between the two types of instruments was less than 1.3% for the AOD and less than 4% for the single scattering albedo below the wavelength of 670 nm. There is a difference between the volume size distribution patterns derived from two instruments, which is probablely due to difference of measurement protocols and inversion algorithms for the respective instruments. AOP under three distinct weather conditions (background, haze, and dust days) over Beijing were compared by using the retrieved skyradiometer and sunphotometer data combined with MODIS satellite results, pyranometer measurements, PM10 measurements, and backtrajectory analysis. The results show that the significant difference of AOP under background, haze, and dust days over Beijing is probablely due to different aerosol components under distinct weather conditions

Global Analysis of Aerosol Properties Above Clouds

The seasonal and spatial varability of Aerosol Above Cloud (AAC) properties are derived from passive satellite data for the year 2008. A significant amount of aerosols are transported above liquid water clouds on the global scale. For particles in the fine mode (i.e., radius smaller than 0.3 m), including both clear sky and AAC retrievals increases the global mean aerosol optical thickness by 25(+/- 6%). The two main regions with man-made AAC are the tropical Southeast Atlantic, for biomass burning aerosols, and the North Pacific, mainly for pollutants. Man-made AAC are also detected over the Arctic during the spring. Mineral dust particles are detected above clouds within the so-called dust belt region (5-40 N). AAC may cause a warming effect and bias the retrieval of the cloud properties. This study will then help to better quantify the impacts of aerosols on clouds and climate

On the Derivation of Vector Radiative Transfer Equation for Polarized Radiative Transport in Graded Index Media

Light transport in graded index media follows a curved trajectory determined by the Fermat's principle. Besides the effect of variation of the refractive index on the transport of radiative intensity, the curved ray trajectory will induce geometrical effects on the transport of polarization ellipse. This paper presents a complete derivation of vector radiative transfer equation for polarized radiation transport in absorption, emission and scattering graded index media. The derivation is based on the analysis of the conserved quantities for polarized light transport along curved trajectory and a novel approach. The obtained transfer equation can be considered as a generalization of the classic vector radiative transfer equation that is only valid for uniform refractive index media. Several variant forms of the transport equation are also presented, which include the form for Stokes parameters defined with a fixed reference and the Eulerian forms in the ray coordinate and in several common orthogonal coordinate systems.Comment: This paper has been submitted to JQSR

Comparison of aerosol optical properties above clouds between POLDER and AeroCom models over the South East Atlantic Ocean during the fire season

Aerosol properties above clouds have been retrieved over the South East Atlantic Ocean during the fire season 2006 using satellite observations from POLDER (Polarization and Directionality of Earth Reflectances). From June to October, POLDER has observed a mean Above-Cloud Aerosol Optical Thickness (ACAOT) of 0.28 and a mean Above-Clouds Single Scattering Albedo (ACSSA) of 0.87 at 550 nm. These results have been used to evaluate the simulation of aerosols above clouds in 5 AeroCom (Aerosol Comparisons between Observations and Models) models (GOCART, HadGEM3, ECHAM5-HAM2, OsloCTM2 and SPRINTARS). Most models do not reproduce the observed large aerosol load episodes. The comparison highlights the importance of the injection height and the vertical transport parameterizations to simulate the large ACAOT observed by POLDER. Furthermore, POLDER ACSSA is best reproduced by models with a high imaginary part of black carbon refractive index, in accordance with recent recommendations

Remote sensing of aerosols by using polarized, directional and spectral measurements within the A-Train: the PARASOL mission

Instruments dedicated to aerosol monitoring are recently available and the POLDER (POLarization and Directionality of the Earth's Reflectances) instrument on board the PARASOL (Polarization & Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) mission is one of them. By measuring the spectral, angular and polarization properties of the radiance at the top of the atmosphere, in coordination with the other A-Train instruments, PARASOL provides the aerosol optical depths (AOD) as well as several optical and microphysical aerosol properties. The instrument, the inversion schemes and the list of aerosol parameters are described. Examples of retrieved aerosol parameters are provided as well as innovative approaches and further inversion techniques

Aerosol Seasonal Variations over Urban-Industrial Regions in Ukraine According to AERONET and POLDER Measurements

The paper presents an investigation of aerosol seasonal variations in several urban-industrial regions in Ukraine. Our analysis of seasonal variations of optical and physical aerosol parameters is based on the sun-photometer 2008-2013 data from two urban ground-based AERONET (AErosol RObotic NETwork) sites in Ukraine (Kyiv, Lugansk) as well as on satellite POLDER instrument data for urban-industrial areas in Ukraine. We also analyzed the data from one AERONET site in Belarus (Minsk) in order to compare with the Ukrainian sites. Aerosol amount and optical depth (AOD) values in the atmosphere columns over the large urbanized areas like Kyiv and Minsk have maximum values in the spring (April-May) and late summer (August), whereas minimum values are observed in late autumn. The results show that fine-mode particles are most frequently detected during the spring and late summer seasons. The analysis of the seasonal AOD variations over the urban-industrial areas in the eastern and central parts of Ukraine according to both ground-based and POLDER data exhibits the similar traits. The seasonal variation similarity in the regions denotes the resemblance in basic aerosol sources that are closely related to properties of aerosol particles. The behavior of basic aerosol parameters in the western part of Ukraine is different from eastern and central regions and shows an earlier appearance of the spring and summer AOD maxima. Spectral single-scattering albedo, complex refractive index and size distribution of aerosol particles in the atmosphere column over Kyiv have different behavior for warm (April-October) and cold seasons. The seasonal features of fine and coarse aerosol particle behavior over the Kyiv site were analyzed. A prevailing influence of the fine-mode particles on the optical properties of the aerosol layer over the region has been established. The back-trajectory and cluster analysis techniques were applied to study the seasonal back trajectories and prevailing directions of the arrived air mass for the Kyiv and Minsk sites

Reduction of Aerosol Absorption in Beijing Since 2007 from MODIS and AERONET

An analysis of the time series of MODIS-based and AERONET aerosol records over Beijing reveals two distinct periods, before and after 2007. The MODIS data from both the Terra and Aqua satellites were processed with the new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. A comparison of MAIAC and AERONET AOT shows that whereas MAIAC consistently underestimated peak AOT values by 10-20% in the prior period, the bias mostly disappears after mid-2007. Independent analysis of the AERONET dataset reveals little or no change in the effective radii of the fine and coarse fractions and of the Angstrom exponent. At the same time, it shows an increasing trend in the single scattering albedo, by approx.0.02 in 9 years. As MAIAC was using the same aerosol model for the entire 2000-2010 period, the decrease in AOT bias after 2007 can be explained only by a corresponding decrease of aerosol absorption caused by a reduction in local black carbon emissions. The observed changes correlate in time with the Chinese government's broad measures to improve air quality in Beijing during preparations for the Summer Olympics of 2008

Preparation of polycaprolactone nanoparticles via supercritical carbon dioxide extraction of emulsions

Polycaprolactone (PCL) nanoparticles were produced via supercritical fluid extraction of emulsions (SFEE) using supercritical carbon dioxide (scCO2). The efficiency of the scCO2 extraction was investigated and compared to that of solvent extraction at atmospheric pressure. The effects of process parameters including polymer concentration (0.6–10% w/w in acetone), surfactant concentration (0.07 and 0.14% w/w) and polymer-to-surfactant weight ratio (1:1–16:1 w/w) on the particle size and surface morphology were also investigated. Spherical PCL nanoparticles with mean particle sizes between 190 and 350 nm were obtained depending on the polymer concentration, which was the most important factor where increase in the particle size was directly related to total polymer content in the formulation. Nanoparticles produced were analysed using dynamic light scattering and scanning electron microscopy. The results indicated that SFEE can be applied for the preparation of PCL nanoparticles without agglomeration and in a comparatively short duration of only 1 h

Protein adsorption on preadsorbed polyampholytic monolayers

The adsorption behaviour of five different globular proteins on pure silicon substrates and on preadsorbed polyampholytic monolayers has been investigated as a function of protein concentration. The prelayers were prepared by adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly ((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA). This polyampholyte adsorbs in densely packed micelles directly from aqueous solution. Ellipsometry was used to determine the amount of adsorbed polyampholyte and protein. While ATR-IR spectroscopy gives information about the adsorption and desorption behaviour of the preadsorbed polyampholytic layer, the lateral structures of the dried films were investigated by scanning force microscopy (SFM). The amount of protein adsorbed was found to be strongly influenced by the preadsorbed polyampholyte compared to the adsorption on the pure silicon substrates. No displacement of the polyampholyte by the proteins was detected. In most cases the protein adsorption was reduced by the preadsorbed polyampholytic layer. The observed trends are explained by the change in electrostatic and hydrophilic characteristics of the substrates. Furthermore, the entropy of adsorption has to be taken into account.Peer reviewe