scholarly journals Investigation of a Saharan dust plume in Western Europe by remote sensing and transport modelling

2021 ◽  
Author(s):  
Hengheng Zhang ◽  
Frank Wagner ◽  
Harald Saathoff ◽  
Heike Vogel ◽  
Gholam Ali Hoshyaripour ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Western Europe ◽  
Saharan Dust ◽  
Dust Particles ◽  
Depolarization Ratio ◽  
Backscatter Coefficient ◽  
Lidar Ratio ◽  
Sun Photometer

Abstract. The evolution and the properties of a Saharan dust plume were studied near the city of Karlsruhe in south-west Germany (8.4298° E, 49.0953° N) from April 7 to 9, 2018 combining a scanning LIDAR (90°, 30°), a vertical LIDAR (90°), a sun photometer, and the transport model ICON-ART. The LIDAR measurements show that the dust particles had backscatter coefficients of 0.86 ± 0.14 Mm−1 Sr−1, an extinction coefficient of 40 ± 0.8 Mm−1, a LIDAR ratio of 46 ± 5 sr, and a particle depolarization ratio of 0.33 ± 0.07. These values are in good agreement with those obtained in previous studies of Saharan dust plumes in Western Europe. Compared to the remote sensing measurements, the model simulation predicts the plume arrival time, its layer height, and structure very well but overestimates the backscatter coefficient. In this manuscript, we discuss the complementarity and advantages of the different measurement methods as well model simulations to predict Saharan dust plumes. Main conclusions are that the ICON-ART model can predict the structure of Saharan dust plumes very well but overestimates the backscatter coefficients by a factor of 2.2 ± 0.16 at 355 nm and underestimates the aerosol optical depth (AOD) by a factor of 1.5 ± 0.11 at 340 nm for this Saharan dust plume event. Employing a scanning aerosol LIDAR allows determining backscatter coefficient, particle depolarization ratio and especially LIDAR ratio of Saharan dust both for daytime and nighttime independently. Combining LIDAR with sun photometer data allows constraining aerosol optical depth in different ways and determining column integrated LIDAR ratios. These comprehensive datasets allow for a better understanding of Saharan dust plumes in Western Europe.

scholarly journals The potential of elastic and polarization lidars to retrieve extinction profiles

2020 ◽  
Vol 13 (2) ◽  
pp. 893-905 ◽  
Author(s):  
Elina Giannakaki ◽  
Panos Kokkalis ◽  
Eleni Marinou ◽  
Nikolaos S. Bartsotas ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Dust Particles ◽  
Depolarization Ratio ◽  
Lidar System ◽  
Lidar Measurements ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio ◽  
Aerosol Types ◽  
532 Nm

Abstract. A new method, called ElEx (elastic extinction), is proposed for the estimation of extinction coefficient lidar profiles using only the information provided by the elastic and polarization channels of a lidar system. The method is applicable to lidar measurements both during daytime and nighttime under well-defined aerosol mixtures. ElEx uses the particle backscatter profiles at 532 nm and the vertically resolved particle linear depolarization ratio measurements at the same wavelength. The particle linear depolarization ratio and the lidar ratio values of pure aerosol types are also taken from literature. The total extinction profile is then estimated and compared well with Raman retrievals. In this study, ElEx was applied in an aerosol mixture of marine and dust particles at Finokalia station during the CHARADMExp campaign. Any difference between ElEx and Raman extinction profiles indicates that the nondust component could be probably attributed to polluted marine or polluted continental aerosols. Comparison with sun photometer aerosol optical depth observations is performed as well during daytime. Differences in the total aerosol optical depth are varying between 1.2 % and 72 %, and these differences are attributed to the limited ability of the lidar to correctly represent the aerosol optical properties in the near range due to the overlap problem.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – a lidar study during SALTRACE

2016 ◽  
Vol 16 (18) ◽  
pp. 11535-11546 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Mean Values ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high-accuracy measurements of the linear depolarization ratio down to about 200 m above ground level, the dust volume fraction and the dust mass concentration within the convective marine boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information on the convective marine boundary layer height and the meteorological situation within the convective marine boundary layer. We investigate the lidar-derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find mean values of 0.04 (SD 0.03) and 0.05 (SD 0.04) at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and (26 ± 5) sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the convective marine boundary layer we find that most values were between 20 and 50 µgm−3. On most days the dust contribution to total aerosol volume was about 30–40 %. Comparing the dust contribution to the column-integrated sun-photometer measurements we see a correlation between high dust contribution, high total aerosol optical depth and a low Angström exponent, and of low dust contribution with low total aerosol optical depth.

scholarly journals The potential of elastic/polarization lidars to retrieve extinction profiles

2019 ◽  
Author(s):  
Elina Giannakaki ◽  
Panos Kokkalis ◽  
Eleni Marinou ◽  
Nikolaos S. Bartsotas ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Dust Particles ◽  
Depolarization Ratio ◽  
Dust Component ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio ◽  
Aerosol Types ◽  
532 Nm

Abstract. In this study we estimate the particle extinction profiles at Finokalia, Crete, using only the information provided by the elastic and polarization channels of a PollyXT lidar system. Most of the time Finokalia site is affected by only two aerosol types, i.e. marine and dust particles. These two aerosol types, having different optical properties, permit the separation of aerosol mixture. The proposed method uses the particle backscatter profiles at 532 nm and the vertically resolved particle linear depolarization ratio measurements at the same wavelength. The particle linear depolarization ratio and the lidar ratio values of pure aerosol types are taken from literature. The total extinction profile is then estimated and compared well with Raman retrievals. Any difference between the proposed methodology and Raman extinction profiles indicates that the non-dust component could be probably attributed to polluted marine or polluted continental aerosols. Comparison with sun-photometric aerosol optical depth observations is performed as well during daytime with reasonable differences between the two instruments. Differences in the total aerosol optical depth is attributed to the limited ability of the lidar to correctly represent the aerosol optical properties in the near range due to overlap problem.

scholarly journals Extreme Saharan dust event over the southern Iberian Peninsula in september 2007: active and passive remote sensing from surface and satellite

2009 ◽  
Vol 9 (4) ◽  
pp. 15673-15723
Author(s):  
J. L. Guerrero-Rascado ◽  
F. J. Olmo ◽  
I. Avilés-Rodríguez ◽  
F. Navas-Guzmán ◽  
D. Pérez-Ramírez ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Iberian Peninsula ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Saharan Dust ◽  
Dust Event ◽  
Passive Remote Sensing ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. This study investigates aerosol optical properties during the extreme Saharan dust event detected from 3 to 7 September 2007 over Granada, southern Iberian Peninsula, with both active and passive remote sensing instrumentation from surface and satellite. The intensity of the event was visualized on the aerosol optical depth series obtained by the sun-photometer Cimel CE 318-4 operated at Granada in the framework of AERONET from August 2004 until December 2008 (level 2 data). A combination of large aerosol optical depth (0.86–1.50) at 500 nm, and reduced Angström exponent (0.1–0.25) in the range 440–870 nm, was detected on 6 September during daytime. This Saharan dust event also affected other Iberian Peninsula stations included in AERONET (El Arenosillo and Évora stations). During the most intense stage, on 6 September, maximum aerosol backscatter values were a factor of 8 higher than other maxima during this Saharan dust event. Values up to 1.5×10−2 km−1 sr−1 at 355 and 532 nm were detected in the layer with the greatest aerosol load between 3–4 km a.s.l., although aerosol particles were also detected up to 5.5 km a.s.l. In this stage of the event, dust particles at these altitudes showed a backscatter-related Angström exponent between −0.44 and 0.53 for the two spectral intervals considered. The results from different measurements (active/passive and ground-based/satellite) reveal the importance of performing multi-instrumental measurements to properly characterize the contribution of different aerosol types from different sources during extreme events.

scholarly journals Study on Aerosol Optical Depth in Winter and Summer Season in Bhaktapur

1970 ◽  
Vol 8 (1-2) ◽  
pp. 269-276
Author(s):  
Niranjan Prasad Sharma ◽  
Bal Krishna Sapkota ◽  
Binod Bhattarai ◽  
Berit Kjeldstad
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Spectral Dependence ◽  
High Speed ◽  
Summer Season ◽  
Dust Particles ◽  
Minimum Value ◽  
Sun Photometer

Aerosol optical depth in winter and summer season, 2009 was studied in Bhaktapur (Kausaltar). Spectral aerosol optical depth (AOD) measurements were estimated from a Microtops II Sun Photometer. The results indicated high values in summer and low values in winter. It also showed that AOD is larger in shorter wavelength and gradually decreases towards longer wavelength. The increasing value of AOD in summer season may be due to the accumulation of high speed dust particles. The lower values in winter months are due to the reduction of bigger particles. The spectral dependence of AOD on January 27 was found to be 0.64, 0.52, 0.48 and 0.35. The AOD at 340 nm in January and July were 0.63 and 0.62, respectively. The maximum and minimum value of AOD at 340 nm in the month of April and August were recorded as 1.62 and 0.56, respectively.Keywords: Sun photometer; Aerosol; Aerosol optical depth; Angstrom parameters; IrradianceDOI: http://dx.doi.org/10.3126/jie.v8i1-2.5122Journal of the Institute of Engineering Vol. 8, No. 1&2, 2010/2011Page: 269-276Uploaded Date: 20 July, 2011

scholarly journals Optimal use of Prede POM sky radiometer for aerosol, water vapor, and ozone retrievals

2020 ◽  
Author(s):  
Rei Kudo ◽  
Henri Diémoz ◽  
Victor Estellés ◽  
Monica Campanelli ◽  
Masahiro Momoi ◽  
...  
Keyword(s):  
Refractive Index ◽  
Water Vapor ◽  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Asymmetry Factor ◽  
Depolarization Ratio ◽  
Lidar Ratio

Abstract. The Prede POM sky radiometer is a filter radiometer deployed worldwide in the SKYNET international network. A new method called, Skyrad pack MRI version 2 (MRI v2), is here presented, to retrieve aerosol properties (size distribution, real and imaginary parts of the refractive index, single-scattering albedo, asymmetry factor, lidar ratio, and linear depolarization ratio), and water vapor and ozone column concentrations from the sky radiometer measurements. MRI v2 overcomes two limitations of previous methods (Skyrad pack versions 4.2 and 5, and MRI version 1). One is the use of all the wavelengths of 315, 340, 380, 400, 500, 675, 870, 940, 1020, 1627, and 2200 nm, if available from the sky radiometers, for example, in POM-02 models. The previous methods cannot use the wavelengths of 315, 940, 1627, and 2200 nm. This enables us to provide improved estimates of the aerosol optical properties, covering almost all the wavelengths of solar radiation. The other is the use of measurements in the principal plane geometry in addition to the solar almucantar plane geometry that is used in the previous versions. The measurements in the principal plane are regularly performed, however they are currently not exploited despite being useful in the case of small solar zenith angles, when the scattering angle distribution for almucantars becomes too small to yield useful information. Moreover, in the inversion algorithm, MRI v2 optimizes the smoothness constraints of the spectral dependencies of the refractive index and size distribution, and changes the contribution of the diffuse radiances to the cost function according to the aerosol optical depth. These overcome issues with the estimation of the size distribution and single-scattering albedo in the Skyrad pack version 4.2. The scattering model used here allows for non-spherical particles, improving results for mineral dust and permitting to evaluate the depolarization ratio. An assessment of the retrieval uncertainties using synthetic measurement show that best performance is obtained when the aerosol optical depths is larger than 0.2 at 500 nm. Improvements over the Skyrad pack versions 4.2 and 5 are obtained for the retrieved size distribution, imaginary part of the refractive index, single-scattering albedo, and lidar ratio at Tsukuba, Japan, while yielding comparable retrievals of the aerosol optical depth, real part of the refractive index, and asymmetry factor. A radiative closure study using surface solar irradiances from Baseline Surface Radiation Network and the parameters retrieved from MRI v2 showed consistency, with a positive bias of the simulated global irradiance, about +24 Wm−2 (+3 %). Furthermore, the MRI v2 retrievals of the refractive index, single-scattering albedo, asymmetry factor, and size distribution have been found in agreement with integrated profiles of aircraft in-situ measurements of two Saharan dust events at the Cape Verde archipelago, during the SAVEX-D 2015 field campaign.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – A lidar study during SALTRACE

2016 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Depolarization Ratio ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Lidar Ratio ◽  
The Caribbean ◽  
Linear Depolarization Ratio ◽  
532 Nm

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high accurate measurements of the linear depolarization ratio down to about 150–200 m above ground level, the dust volume fraction and the dust mass concentration within the Caribbean boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information of the boundary layer height and the meteorological situation within the boundary layer. We investigate the lidar derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find over all mean values and mean uncertainties of 0.04 ± 0.03 and 0.05 ± 0.04 at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and 26 ± 5 sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the Caribbean boundary layer we find that most values are between 20 and 50 g/m3, and that on most days the dust contribution to total aerosol volume is about 30–40 %. Comparing the dust contribution to the columnintegrated sun-photometer measurements we see a correlation of high dust contribution, high total aerosol optical depth and a corresponding low Angström exponent, and of low dust contribution with low total aerosol optical depth and corresponding high Angström exponent. The relative humidity within the boundary layer was high with values around 80 % on most of the days.

scholarly journals Sun photometer retrievals of Saharan dust properties over Barbados during SALTRACE

2019 ◽  
Vol 19 (23) ◽  
pp. 14571-14583 ◽  
Author(s):  
Carlos Toledano ◽  
Benjamín Torres ◽  
Cristian Velasco-Merino ◽  
Dietrich Althausen ◽  
Silke Groß ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Saharan Dust ◽  
Caribbean Region ◽  
The Sun ◽  
Concentration Data ◽  
The Caribbean ◽  
Sun Photometer ◽  
Dust Events

Abstract. The Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE) was devoted to the investigation of Saharan dust properties over the Caribbean. The campaign took place in June–July 2013. A wide set of ground-based and airborne aerosol instrumentation was deployed at the island of Barbados for a comprehensive experiment. Several sun photometers performed measurements during this campaign: two AERONET (Aerosol Robotic Network) Cimel sun photometers and the Sun and Sky Automatic Radiometer (SSARA). The sun photometers were co-located with the ground-based multi-wavelength lidars BERTHA (Backscatter Extinction lidar Ratio Temperature Humidity profiling Apparatus) and POLIS (Portable Lidar System). Aerosol properties derived from direct sun and sky radiance observations are analyzed, and a comparison with the co-located lidar and in situ data is provided. The time series of aerosol optical depth (AOD) allows identifying successive dust events with short periods in between in which the marine background conditions were observed. The moderate aerosol optical depth in the range of 0.3 to 0.6 was found during the dust periods. The sun photometer infrared channel at the 1640 nm wavelength was used in the retrieval to investigate possible improvements to aerosol size retrievals, and it was expected to have a larger sensitivity to coarse particles. The comparison between column (aerosol optical depth) and surface (dust concentration) data demonstrates the connection between the Saharan Air Layer and the boundary layer in the Caribbean region, as is shown by the synchronized detection of the successive dust events in both datasets. However the differences of size distributions derived from sun photometer data and in situ observations reveal the difficulties in carrying out a column closure study.

scholarly journals Optimal use of the Prede POM sky radiometer for aerosol, water vapor, and ozone retrievals

2021 ◽  
Vol 14 (5) ◽  
pp. 3395-3426
Author(s):  
Rei Kudo ◽  
Henri Diémoz ◽  
Victor Estellés ◽  
Monica Campanelli ◽  
Masahiro Momoi ◽  
...  
Keyword(s):  
Refractive Index ◽  
Water Vapor ◽  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Asymmetry Factor ◽  
Depolarization Ratio ◽  
Lidar Ratio

Abstract. The Prede POM sky radiometer is a filter radiometer deployed worldwide in the SKYNET international network. A new method, called Skyrad pack MRI version 2 (MRI v2), is presented here to retrieve aerosol properties (size distribution, real and imaginary parts of the refractive index, single-scattering albedo, asymmetry factor, lidar ratio, and linear depolarization ratio), water vapor, and ozone column concentrations from the sky radiometer measurements. MRI v2 overcomes two limitations of previous methods (Skyrad pack versions 4.2 and 5, MRI version 1). One is the use of all the wavelengths of 315, 340, 380, 400, 500, 675, 870, 940, 1020, 1627, and 2200 nm if available from the sky radiometers, for example, in POM-02 models. The previous methods cannot use the wavelengths of 315, 940, 1627, and 2200 nm. This enables us to provide improved estimates of the aerosol optical properties, covering almost all the wavelengths of solar radiation. The other is the use of measurements in the principal plane geometry in addition to the solar almucantar plane geometry that is used in the previous versions. Measurements in the principal plane are regularly performed; however, they are currently not exploited despite being useful in the case of small solar zenith angles when the scattering angle distribution for almucantars becomes too small to yield useful information. Moreover, in the inversion algorithm, MRI v2 optimizes the smoothness constraints of the spectral dependencies of the refractive index and size distribution, and it changes the contribution of the diffuse radiances to the cost function according to the aerosol optical depth. This overcomes issues with the estimation of the size distribution and single-scattering albedo in the Skyrad pack version 4.2. The scattering model used here allows for non-spherical particles, improving results for mineral dust and permitting evaluation of the depolarization ratio. An assessment of the retrieval uncertainties using synthetic measurements shows that the best performance is obtained when the aerosol optical depth is larger than 0.2 at 500 nm. Improvements over the Skyrad pack versions 4.2 and 5 are obtained for the retrieved size distribution, imaginary part of the refractive index, single-scattering albedo, and lidar ratio at Tsukuba, Japan, while yielding comparable retrievals of the aerosol optical depth, real part of the refractive index, and asymmetry factor. A radiative closure study using surface solar irradiances from the Baseline Surface Radiation Network and the parameters retrieved from MRI v2 showed consistency, with a positive bias of the simulated global irradiance of about +1 %. Furthermore, the MRI v2 retrievals of the refractive index, single-scattering albedo, asymmetry factor, and size distribution have been found to be in agreement with integrated profiles of aircraft in situ measurements of two Saharan dust events at the Cape Verde archipelago during the Sunphotometer Airborne Validation Experiment in Dust (SAVEX-D) 2015 field campaign.

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