scholarly journals Atmospheric aerosol characterization with a ground-based SPEX spectropolarimetric instrument

2014 ◽  
Vol 7 (12) ◽  
pp. 4341-4351 ◽  
Author(s):  
G. van Harten ◽  
J. de Boer ◽  
J. H. H. Rietjens ◽  
A. Di Noia ◽  
F. Snik ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Atmospheric Aerosols ◽  
Complex Refractive Index ◽  
Random Noise ◽  
Aerosol Optical Thickness ◽  
Clear Sky ◽  
Field Deployment ◽  
Scattering Phase Function ◽  
Aerosol Parameters ◽  
Low Degrees

Abstract. Characterization of atmospheric aerosols is important for understanding their impact on health and climate. A wealth of aerosol parameters can be retrieved from multi-angle, multi-wavelength radiance and polarization measurements of the clear sky. We developed a ground-based SPEX instrument (groundSPEX) for accurate spectropolarimetry, based on the passive, robust, athermal, and snapshot spectral polarization modulation technique, and is hence ideal for field deployment. It samples the scattering phase function in the principal plane in an automated fashion, using a motorized pan/tilt unit and automatic exposure time detection. Extensive radiometric and polarimetric calibrations were performed, yielding values for both random noise and systematic uncertainties. The absolute polarimetric accuracy at low degrees of polarization is established to be ~5 × 10−3. About 70 measurement sequences have been performed throughout four clear-sky days at Cabauw, the Netherlands. Several aerosol parameters were retrieved: aerosol optical thickness, effective radius, and complex refractive index for fine and coarse mode. The results are in good agreement with the colocated AERONET products, with a correlation coefficient of ρ = 0.932 for the total aerosol optical thickness at 550 nm.

scholarly journals Atmospheric aerosol characterization with a ground-based SPEX spectropolarimetric instrument

2014 ◽  
Vol 7 (6) ◽  
pp. 5741-5768 ◽  
Author(s):  
G. van Harten ◽  
J. de Boer ◽  
J. H. H. Rietjens ◽  
A. Di Noia ◽  
F. Snik ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Atmospheric Aerosols ◽  
Complex Refractive Index ◽  
Random Noise ◽  
Aerosol Optical Thickness ◽  
Clear Sky ◽  
Field Deployment ◽  
Scattering Phase Function ◽  
Aerosol Parameters ◽  
Low Degrees

Abstract. Characterization of atmospheric aerosols is important for understanding their impact on health and climate. A wealth of aerosol parameters can be retrieved from multi-angle, multi-wavelength radiance and polarization measurements of the clear sky. We developed a ground-based SPEX instrument (groundSPEX) for accurate spectropolarimetry, based on the passive, robust, athermal and snapshot spectral polarization modulation technique, and hence ideal for field deployment. It samples the scattering phase function in the principal plane in an automated fashion, using a motorized pan/tilt unit and automatic exposure time detection. Extensive radiometric and polarimetric calibrations were performed, yielding values for both random noise and systematic uncertainties. The absolute polarimetric accuracy at low degrees of polarization is established to be ~ 5 × 10−3. About 70 measurement sequences have been performed throughout four clear-sky days at Cabauw, the Netherlands. Several aerosol parameters were retrieved: aerosol optical thickness, effective radius, and complex refractive index for fine and coarse mode. The results are in good agreement with the co-located AERONET products, with a correlation coefficient of ρ = 0.932 for the total aerosol optical thickness at 550 nm.

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 Retrieval of Aerosol Optical Thickness with Custom Aerosol Model Using SKYNET Data over the Chiba Area

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1144
Author(s):  
Zixuan Xue ◽  
Hiroaki Kuze ◽  
Hitoshi Irie
Keyword(s):  
Radiative Transfer ◽  
Optical Thickness ◽  
Surface Albedo ◽  
Spectral Response ◽  
Aerosol Optical Thickness ◽  
Observation Data ◽  
Aerosol Model ◽  
Clear Sky ◽  
Wide Range ◽  
Sky Conditions

The retrieval of the aerosol optical thickness (AOT) from remotely-sensed data relies on the adopted aerosol model. However, the method of this technique has been rather limited because of the high variability of the surface albedo, in addition to the spatial variability in the aerosol properties over the land surfaces. To overcome unsolved problems, we proposed a method for the visibility-derived AOT estimation from SKYNET-based measurement and daytime satellite images with a custom aerosol model over the Chiba area (35.62° N, 140.10° E), which is located in the greater Tokyo metropolitan area in Japan. Different from conventionally-used aerosol models for the boundary layer, we created a custom aerosol model by using sky-radiometer observation data of aerosol volume size distribution and refractive indices, coupled with spectral response functions (SPFs) of satellite visible bands to alleviate the wide range of path-scattered radiance. We utilized the radiative transfer code 6S to implement the radiative transfer calculation based on the created custom aerosol model. The concurrent data from ground-based measurement are used in the radiative analysis, namely the temporal variation of AOT from SKYNET. The radiative estimation conducted under clear-sky conditions with minimum aerosol loading is used for the determination of the surface albedo, so that the 6S simulation yields a well-defined relation between total radiance and surface albedo. We made look-up tables (LUTs) pixel-by-pixel over the Chiba area for the custom aerosol model to retrieve the satellite AOT distribution based on the surface albedo. Therefore, such a reference of surface albedo generated from clear-sky conditions, in turn, can be employed to retrieve the spatial distribution of AOT on both clear and relatively turbid days. The value for the AOTs retrieved using the custom aerosol model is found to be stable than conventionally-used typical aerosol models, indicating that our method yields substantially better performance.

scholarly journals Enhancement of aerosol characterization using synergy of lidar and sun-photometer coincident observations: the GARRLiC algorithm

2013 ◽  
Vol 6 (8) ◽  
pp. 2065-2088 ◽  
Author(s):  
A. Lopatin ◽  
O. Dubovik ◽  
A. Chaikovsky ◽  
P. Goloub ◽  
T. Lapyonok ◽  
...  
Keyword(s):  
Complex Refractive Index ◽  
Random Noise ◽  
Microphysical Properties ◽  
Aerosol Retrieval ◽  
Sensitivity Tests ◽  
Multi Wavelength ◽  
Fine Mode ◽  
Aerosol Parameters ◽  
Coarse Aerosol ◽  
Combined Data

Abstract. This paper presents the GARRLiC algorithm (Generalized Aerosol Retrieval from Radiometer and Lidar Combined data) that simultaneously inverts coincident lidar and radiometer observations and derives a united set of aerosol parameters. Such synergetic retrieval results in additional enhancements in derived aerosol properties because the back-scattering observations by lidar improve sensitivity to the columnar properties of aerosol, while radiometric observations provide sufficient constraints on aerosol amount and type that are generally missing in lidar signals. GARRLiC is based on the AERONET algorithm, improved to invert combined observations by radiometer and multi-wavelength elastic lidar observations. The algorithm is set to derive not only the vertical profile of total aerosol concentration but it also differentiates between the contributions of fine and coarse modes of aerosol. The detailed microphysical properties are assumed height independent and different for each mode and derived as a part of the retrieval. The GARRLiC inversion retrieves vertical distribution of both fine and coarse aerosol concentrations as well as the size distribution and complex refractive index for each mode. The potential and limitations of the method are demonstrated by the series of sensitivity tests. The effects of presence of lidar data and random noise on aerosol retrievals are studied. Limited sensitivity to the properties of the fine mode as well as dependence of retrieval accuracy on the aerosol optical thickness were found. The practical outcome of the approach is illustrated by applications of the algorithm to the real lidar and radiometer observations obtained over Minsk AERONET site.

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

2009 ◽  
Vol 2 (2) ◽  
pp. 593-608 ◽  
Author(s):  
N. Y. Chubarova
Keyword(s):  
Optical Thickness ◽  
Spectral Region ◽  
Single Scattering ◽  
Temporal Variations ◽  
Aerosol Optical Thickness ◽  
Asymmetry Factor ◽  
Mean Values ◽  
Uv Irradiance ◽  
Aerosol Parameters

Abstract. Using the aerosol optical thickness at 550 nm (τ550) from MODIS (collection 5) for the 2000–2008 period combined with the aerosol products from the ground-based AERONET network since 1996, monthly mean values of 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 (−1%–−17%) with a minimum towards the northwest and maxima over several southern local areas (Northern Italy, etc.) during the warm period.

scholarly journals Validation of SCIAMACHY top-of-atmosphere reflectance for aerosol remote sensing using MERIS L1 data

2007 ◽  
Vol 7 (1) ◽  
pp. 97-106 ◽  
Author(s):  
W. von Hoyningen-Huene ◽  
A. A. Kokhanovsky ◽  
M. W. Wuttke ◽  
M. Buchwitz ◽  
S. Noël ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Optical Thickness ◽  
Current Data ◽  
Aerosol Optical Thickness ◽  
Aerosol Retrieval ◽  
L1 Data ◽  
The Status ◽  
Aerosol Remote Sensing ◽  
Scanning Imaging ◽  
Aerosol Parameters

Abstract. Aerosol remote sensing is very much dependent on the accurate knowledge of the top-of-atmosphere (TOA) reflectance measured by a particular instrument. The status of the calibration of such an instrument is reflected in the quality of the aerosol retrieval. Current data of the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument (operated with the data processor version 5 and earlier) give too small values of the TOA reflectance, compared e.g. to data from MERIS (Medium Resolution Imaging Spectrometer), both operating on ENVISAT (ENVIronmental SATellite). This effect causes retrievals of wrong aerosol optical thickness and disables the processing of aerosol parameters. From an inter-comparison of MERIS and SCIAMACHY TOA reflectance, for collocated scenes correction factors are derived to improve the insufficient SCIAMACHY L1 data calibration for data obtained with the processor 5 for the purpose of aerosol remote sensing. The corrected reflectance has been used for tests of remote sensing of the aerosol optical thickness by the BAER (Bremen AErosol Retrieval) approach using SCIAMACHY data.

Mathematical modelling of remote detection of molecular air pollutants

1987 ◽  
Vol 52 (6) ◽  
pp. 1397-1406
Author(s):  
František Zrcek ◽  
Milan Horák
Keyword(s):  
Atmospheric Aerosols ◽  
Air Pollutants ◽  
Complex Refractive Index ◽  
Mie Scattering ◽  
Heat Emission ◽  
Remote Detection ◽  
Radiation Absorption ◽  
Variable Concentration ◽  
Lidar Equation ◽  
Optical Pathway

A model of remote detection of molecular air pollutants is devised based on the lidar equation. The various kinds of interaction of radiation with matter, viz. absorption, induced fluorescence, and Raman scattering, are taken into account; detection of either scattered or reflected signal is considered. The reflection is assumed to be either axial, using a retroreflector, or omnidirectional from a field target. Based on this model, an algorithm was set up for simulation of the different variants of the experiment, making allowance for a generally variable concentration of the compound along the optical pathway of the light beam. The basic atmospheric processes, viz. radiation absorption by the backround, heat emission, turbulence, and the effect of atmospheric aerosols, are treated, and the last of them is found to play the major role. Aerosols are looked upon as a source of the Mie scattering and they are described by distribution equations with respect to the particle size and the complex refractive index. The variable concentration of the aerosol along the optical pathway and the simultaneous effect of a higher numberof aerosol types are included.

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