scholarly journals Aerosol seasonal variations over urban sites in Ukraine and Belarus according to AERONET and POLDER measurements

2013 ◽  
Vol 6 (6) ◽  
pp. 10731-10759 ◽  
Author(s):  
G. Milinevsky ◽  
V. Danylevsky ◽  
V. Bovchaliuk ◽  
A. Bovchaliuk ◽  
Ph. Goloub ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Seasonal Variations ◽  
Urban Areas ◽  
Late Summer ◽  
Single Scattering ◽  
Aerosol Optical Thickness ◽  
Saharan Dust ◽  
Coarse Mode ◽  
Modal Radius ◽  
Urban Sites

Abstract. The paper presents an investigation of aerosol seasonal variations in several urban sites in the East European region. Our analysis of seasonal variations of optical and physical aerosol parameters is based on the sun-photometer 2008–2012 data from three urban ground-based AERONET sites in Ukraine (Kyiv, Kyiv-AO, and Lugansk) and one site in Belarus (Minsk), as well as on satellite POLDER instrument data for urban areas in Ukraine. Aerosol amount and optical thickness values exhibit peaks in the spring (April–May) and late summer (August), whereas minimum values are seen in late autumn over the Kyiv and Minsk sites. The results show that aerosol fine mode particles are most frequently detected during the spring and late summer seasons. The seasonal variation similarity in the two regions points to the resemblance in basic aerosol sources which are closely related to properties of aerosol particles. However the aerosol amount and properties change noticeably from year to year and from region to region. The analysis of seasonal aerosol optical thickness variations over the urban sites in the eastern and western parts of Ukraine according to both ground-based and POLDER data exhibits the same traits. In particular, over Kyiv, the values of the Angstrom exponent are lower in April of 2011 than in 2009 and 2010, while aerosol optical thickness values are almost the same, which can be explained by an increase in the amount of coarse mode particles in the atmosphere, such as Saharan dust. Moreover, the coarse mode particles prevailed over suburbs and the center of Kyiv during a third of all available days of observation in 2012. In general, the fine and coarse mode particles' modal radii averaged over 2008–2012 range from 0.1 to 0.2 μm and 2 to 5 μm, respectively, during the period from April to September. The single scattering albedo and refractive index values of these particles correspond to a mix of urban-industrial, biomass burning, and dust aerosols. In addition, strongly absorbing particles were observed in the period from October to March, and the modal radius of fine and coarse mode particles changed from month to month widely.

Consistent retrieval of cloud/aerosol single scattering properties and surface reflectance

2021 ◽  
Author(s):  
Marta Luffarelli ◽  
Yves Govaerts
Keyword(s):  
Radiative Transfer ◽  
Optical Thickness ◽  
Solution Space ◽  
Single Scattering ◽  
Aerosol Optical Thickness ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Surface Reflectance ◽  
Earth System ◽  
System Components

<p>The CISAR (Combined Inversion of Surface and AeRosols) algorithm is exploited in the framework of the ESA Aerosol Climate Change Initiatiave (CCI) project, aiming at providing a set of atmospheric (cloud and aerosol) and surface reflectance products derived from S3A/SLSTR observations using the same radiative transfer physics and assumptions. CISAR is an advance algorithm developed by Rayference originally designed for the retrieval of aerosol single scattering properties and surface reflectance from both geostationary and polar orbiting satellite observations.  It is based on the inversion of a fast radiative transfer model (FASTRE). The retrieval mechanism allows a continuous variation of the aerosol and cloud single scattering properties in the solution space.</p><p> </p><p>Traditionally, different approaches are exploited to retrieve the different Earth system components, which could lead to inconsistent data sets. The simultaneous retrieval of different atmospheric and surface variables over any type of surface (including bright surfaces and water bodies) with the same forward model and inversion scheme ensures the consistency among the retrieved Earth system components. Additionally, pixels located in the transition zone between pure clouds and pure aerosols are often discarded from both cloud and aerosol algorithms. This “twilight zone” can cover up to 30% of the globe. A consistent retrieval of both cloud and aerosol single scattering properties with the same algorithm could help filling this gap.</p><p> </p><p>The CISAR algorithm aims at overcoming the need of an external cloud mask, discriminating internally between aerosol and cloud properties. This approach helps reducing the overestimation of aerosol optical thickness in cloud contaminated pixels. The surface reflectance product is delivered both for cloud-free and cloudy observations.  </p><p> </p><p>Global maps obtained from the processing of S3A/SLSTR observations will be shown. The SLSTR/CISAR products over events such as, for instance, the Australian fire in the last months of 2019, will be discussed in terms of aerosol optical thickness, aerosol-cloud discrimination and fine/coarse mode fraction.</p>

scholarly journals Retrieval of spectral aerosol optical thickness over land using ocean color sensors MERIS and SeaWiFS

2010 ◽  
Vol 3 (3) ◽  
pp. 2107-2164 ◽  
Author(s):  
W. von Hoyningen-Huene ◽  
J. Yoon ◽  
M. Vountas ◽  
L. G. Istomina ◽  
G. Rohen ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Vegetation Index ◽  
Single Scattering ◽  
Aerosol Optical Thickness ◽  
Visible Range ◽  
Surface Reflectance ◽  
Spectral Determination ◽  
Aerosol Retrieval ◽  
Phase Functions

Abstract. For the determination of aerosol optical thickness (AOT) Bremen AErosol Retrieval (BAER) has been developed. Method and main influences on the aerosol retrieval are described together with validation and results. The retrieval separates the spectral aerosol reflectance from surface and Rayleigh path reflectance for the shortwave range of the measured spectrum of top-of-atmosphere reflectance less than 0.670 μm. The advantage of MERIS (Medium Resolution Imaging Spectrometer on ENVISAT) and SeaWiFS (Sea viewing Wide Fiels Sensor on OrbView-2) observations are the existence of several spectral channels in the blue and visible range enabling the spectral determination of AOT in 7 (or 6) channels (0.412–0.670 μm) and additionally channels in the NIR, which can be used to characterize the surface properties. A dynamical spectral surface reflectance model for different surface types is used to obtain the spectral surface reflectance for this separation. Normalized differential vegetation index (NDVI), taken from the satellite observations, is the model input. Further surface BRDF is considered by the Raman-Pinty-Verstraete (RPV) model. Spectral AOT is obtained from aerosol reflectance using look-up-tables, obtained from radiative transfer calculations with given aerosol phase functions and single scattering albedos either from aerosol models, given by OPAC or from experimental campaigns. Validations of the obtained AOT retrieval results with AERONET data over Europe gave a preference for experimental phase functions derived from almucantar measurements. Finally long-term observations of SeaWiFS have been investigated for trends in AOT.

scholarly journals Seasonal distribution of aerosol properties over Europe and their impact on UV irradiance

2009 ◽  
Vol 2 (4) ◽  
pp. 1863-1899
Author(s):  
N. Y. Chubarova
Keyword(s):  
Optical Thickness ◽  
Spectral Region ◽  
Single Scattering ◽  
Temporal Variations ◽  
Aerosol Optical Thickness ◽  
Asymmetry Factor ◽  
Uv Irradiance ◽  
Aerosol Parameters ◽  
Radiative Transfer Modeling

Abstract. Using the aerosol optical thickness at 550 nm (τ550) from MODIS (collection 5) combined with the aerosol products from the ground-based AERONET network, key aerosol parameters have been obtained with 1 degree resolution over Europe. Additional tests have revealed a satisfactory quality of the MODIS data, except in a few cases. Quality assured AERONET data are used for evaluating the Angstrom exponent, single scattering albedo and asymmetry factor, and for validating the final aerosol optical thickness in the UV spectral region. A method for extrapolating the aerosol parameters into the UV spectral region is discussed. The aerosol optical thickness distributions are considered together with meteorological fields from NOAA_NCEP_CPC_CAMS_OPI climatology. The τ340 is shown to vary significantly from approximately 0.01 to 0.9 depending on the season and location. Permanent elevated aerosol loading over several industrial areas is observed, which agrees with the output of chemical transport models. Using radiative transfer modeling, monthly mean UV loss due to aerosol was estimated. The absolute decrease in UV indices varies from less than 0.1 to 1.5. The relative UV attenuation has large spatial and temporal variations (from −1% to −17%) with a minimum towards the northwest and maxima over several southern local areas (Northern Italy, etc.) during the warm period.

scholarly journals Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their Direct Radiative Effect

2014 ◽  
Vol 14 (18) ◽  
pp. 25533-25579 ◽  
Author(s):  
F. Peers ◽  
F. Waquet ◽  
C. Cornet ◽  
P. Dubuisson ◽  
F. Ducos ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Single Scattering ◽  
Saharan Dust ◽  
Aerosol Layer ◽  
Radiative Effect ◽  
East Atlantic ◽  
Aerosol Absorption ◽  
Cloud Optical Thickness ◽  
The Mean ◽  
Aerosol Properties

Abstract. The albedo of clouds and the aerosol absorption are key parameters to evaluate the direct radiative effect of an aerosol layer above clouds. While most of the retrievals of above clouds aerosol characteristics rely on assumptions on the aerosol properties, this study offers a new method to evaluate aerosol and cloud optical properties simultaneously (i.e. aerosol and cloud optical thickness, aerosol single scattering albedo and angström exponent). It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER – Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate the scattering aerosol optical thickness and the aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and the cloud optical thickness. In addition, a procedure has been developed to process the shortwave direct radiative effect of aerosols above clouds based on exact modeling. Besides the three case studies (i.e. biomass burning aerosols from Africa and Siberia and Saharan dust), both algorithms have been applied on the South East Atlantic Ocean and results have been averaged through August 2006. The mean direct radiative effect is found to be 33.5 W m−2. Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not much the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

scholarly journals A new method for deriving aerosol solar radiative forcing and its first application within MILAGRO/INTEX-B

2010 ◽  
Vol 10 (16) ◽  
pp. 7829-7843 ◽  
Author(s):  
K. S. Schmidt ◽  
P. Pilewskie ◽  
R. Bergstrom ◽  
O. Coddington ◽  
J. Redemann ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Radiative Forcing ◽  
Field Experiments ◽  
Single Scattering ◽  
Aerosol Optical Thickness ◽  
Spectral Irradiance ◽  
New Method ◽  
Horizontal Gradient ◽  
Aerosol Radiative Forcing ◽  
Aerosol Forcing

Abstract. We introduce a method for deriving aerosol spectral radiative forcing along with single scattering albedo, asymmetry parameter, and surface albedo from airborne vertical profile measurements of shortwave spectral irradiance and spectral aerosol optical thickness. The new method complements the traditional, direct measurement of aerosol radiative forcing efficiency from horizontal flight legs below gradients of aerosol optical thickness, and is particularly useful over heterogeneous land surfaces and for homogeneous aerosol layers where the horizontal gradient method is impractical. Using data collected by the Solar Spectral Flux Radiometer (SSFR) and the Ames Airborne Tracking Sunphotometer (AATS-14) during the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiment, we validate an over-ocean spectral aerosol forcing efficiency from the new method by comparing with the traditional method. Retrieved over-land aerosol optical properties are compared with in-situ measurements and AERONET retrievals. The spectral forcing efficiencies over ocean and land are remarkably similar and agree with results from other field experiments.

scholarly journals Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

2015 ◽  
Vol 15 (8) ◽  
pp. 4179-4196 ◽  
Author(s):  
F. Peers ◽  
F. Waquet ◽  
C. Cornet ◽  
P. Dubuisson ◽  
F. Ducos ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Case Studies ◽  
Biomass Burning ◽  
Optical Thickness ◽  
Single Scattering ◽  
Original Method ◽  
Saharan Dust ◽  
Radiative Effect ◽  
Cloud Optical Thickness ◽  
The Mean

Abstract. This study presents an original method to evaluate key parameters for the estimation of the direct radiative effect (DRE) of aerosol above clouds: the absorption of the the cloud albedo. It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER – Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate scattering aerosol optical thickness and aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and cloud optical thickness. The retrieval of aerosol and clouds properties (i.e., aerosol and cloud optical thickness, aerosol single scattering albedo and Ångström exponent) is restricted to homogeneous and optically thick clouds (cloud optical thickness larger than 3). In addition, a procedure has been developed to process the shortwave DRE of aerosols above clouds. Three case studies have been selected: a case of absorbing biomass burning aerosols above clouds over the southeast Atlantic Ocean, a Siberian biomass burning event and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies, both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. The mean DRE is found to be 33.5 W m−2 (warming). Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not greatly the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

scholarly journals Seasonal variability of aerosol optical properties observed by means of a Raman lidar at an EARLINET site over Northeastern Spain

2011 ◽  
Vol 11 (1) ◽  
pp. 175-190 ◽  
Author(s):  
M. Sicard ◽  
F. Rocadenbosch ◽  
M. N. M. Reba ◽  
A. Comerón ◽  
S. Tomás ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Planetary Boundary Layer ◽  
Optical Thickness ◽  
Seasonal Variability ◽  
Aerosol Optical Thickness ◽  
Saharan Dust ◽  
Raman Lidar ◽  
Aerosol Optical Properties ◽  
Lidar Ratio

Abstract. The annual and seasonal variability of aerosol optical properties observed by means of a Raman lidar over Northeastern Spain has been assessed. The lidar representativeness has first been checked against sun-photometer measurements in terms of aerosol optical thickness. Then the annual cycle and the seasonal variability of the planetary boundary layer aerosol optical thickness and its fraction compared to the columnar optical thickness, the lidar ratio, the backscatter-related Ångström exponent and the planetary boundary layer height are analyzed and discussed. Winter and summer mean profiles of extinction, backscatter and lidar ratio retrieved with the Raman algorithm are presented. The analysis shows the impact of most of the natural events (Saharan dust intrusions, wildfires, etc.) and meteorological situations (summer anticyclonic situation, the formation of the Iberian thermal low, winter long-range transport from North Europe and/or North America, re-circulation flows, etc.) occurring in the Barcelona area. A detailed study of a special event including a combined intrusion of Saharan dust and biomass-burning particles proves the suitability of combining the retrieval of aerosol optical properties from Raman and pure elastic lidar measurements to discriminate spatially different types of aerosols and to follow their spatial and temporal evolution.

scholarly journals Aerosol vertical distribution and optical properties over M'Bour (16.96° W; 14.39° N), Senegal from 2006 to 2008

2009 ◽  
Vol 9 (4) ◽  
pp. 16295-16330 ◽  
Author(s):  
J.-F. Léon ◽  
Y. Derimian ◽  
I. Chiapello ◽  
D. Tanré ◽  
T. Podvin ◽  
...  
Keyword(s):  
Optical Properties ◽  
Vertical Distribution ◽  
Biomass Burning ◽  
Optical Thickness ◽  
North Atlantic Ocean ◽  
Late Summer ◽  
Ground Level ◽  
Dust Storms ◽  
Aerosol Optical Thickness ◽  
Aerosol Layer

Abstract. We present ground-based measurements of aerosol mass, optical properties and vertical extinction profiles acquired in M'Bour, Senegal (16.96° W; 14.39° N) from January 2006 to September 2008. This place of the word is all year long affected by the export of mineral dust as it moves westward to the north Atlantic ocean. The maximum in the dust activity is observed in summer (June–July), corresponding to a maximum in the aerosol optical thickness (above 0.5) and single scattering albedo (above 0.95). It also corresponds to a maximum in the top altitude of the transported aerosol layer (up to 6 km) and aerosol optical thickness scale height (up to 3.5 km) due to the presence of the Saharan Air Layer located between 2 and 6 km. The late summer shows an additional low level aerosol layer that increases in thickness in autumn. Severe dust storms are also systematically observed in spring (March) but with a lower vertical development and a stronger impact (factor 2 to 3) on the ground-level mass compared to summer. Sporadic events of biomass burning aerosols are observed in winter (January) and particularly in January 2006 when the biomass burning aerosol are advected between 1.5 and 3.5 km high. On average, the seasonal signal in the aerosol optical properties and vertical distribution is very similar from year to year over our 3 year monitoring.

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