Lidar Ratio Derived for Pure Dust Aerosols: Multi-Year Micro Pulse Lidar Observations in a Saharan Dust-Influenced Region

Abstract. We present our combined Raman/elastic backscatter lidar observations which were carried out at the EARLINET station of Thessaloniki, Greece, during the period 2001–2007. The largest optical depths are observed for Saharan dust and smoke aerosol particles. For local and continental polluted aerosols the measurements indicate high aerosol loads. However, measurements associated with the local path indicate enhanced aerosol load within the Planetary Boundary Layer. The lowest value of aerosol optical depth is observed for continental aerosols, from West directions with less free tropospheric contribution. The largest lidar ratios, of the order of 70 sr, are found for biomass burning aerosols. A significant and distinct correlation between lidar ratio and backscatter related Ångström exponent values were estimated for different aerosol categories. Scatter plot between lidar ratio values and Ångström exponent values for local and continental polluted aerosols does not show a significant correlation, with a large variation in both parameters possibly due to variable absorption characteristics of these aerosols. Finally for continental aerosols with west and northwest directions that follow downward movement when arriving at our site constantly low lidar ratios almost independent of size are found.

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Optical properties of different aerosol types: seven years of combined Raman- elastic backscatter lidar measurements in Thessaloniki, Greece

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-2-3027-2009 ◽

2009 ◽

Vol 2 (6) ◽

pp. 3027-3054

Author(s):

E. Giannakaki ◽

D. S. Balis ◽

V. Amiridis ◽

C. Zerefos

Keyword(s):

Saharan Dust ◽

Scatter Plot ◽

Angstrom Exponent ◽

Lidar Measurements ◽

Ångström Exponent ◽

Lidar Ratio ◽

Local Path ◽

Aerosol Types ◽

Lidar Observations ◽

Ångstrom Exponent

Abstract. We present our combined Raman/elastic backscatter lidar observations which were carried out at the EARLINET station of Thessaloniki, Greece, during the period 2001–2007. The largest optical depths are observed for Saharan dust and smoke aerosol loads. For "local" and "continental polluted" aerosols the measurements indicate moderate aerosol loads. However, measurements associated with the "local" path show lower values of free tropospheric contribution (37% versus 46% for "continental polluted") and thus, enhanced aerosol load within the Planetary Boundary Layer. The lowest value of aerosol optical depth is observed for "continental clean" aerosols. The largest lidar ratios, of the order of 70 sr are found for biomass burning aerosols. A significant and distinct correlation between lidar ratio and backscatter related Ångström exponent values was estimated for well defined aerosol categories, which provides a statistical measure of the lidar ratio's dependency on aerosol-size, which is a useful tool for elastic lidar systems. Scatter plot between lidar ratio values and Ångström exponent values for "local" and "continental polluted" aerosols does not show a significant correlation, with a large variation in both parameters possibly due to variable absorption characteristics of these aerosols. Finally for "clean continental" aerosols we found constantly low lidar ratios almost independent of size.

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First triple-wavelength lidar observations of depolarization and extinction-to-backscatter ratios of Saharan dust

10.5194/acp-2021-608 ◽

2021 ◽

Author(s):

Moritz Haarig ◽

Albert Ansmann ◽

Ronny Engelmann ◽

Holger Baars ◽

Dietrich Althausen ◽

...

Keyword(s):

Saharan Dust ◽

Depolarization Ratio ◽

Spectral Slope ◽

Desert Dust ◽

Lidar Measurements ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

First Time ◽

Dust Case ◽

Lidar Observations

Abstract. Two Saharan dust layers observed over Leipzig in February and March 2021 were used to provide the first ever lidar measurements of the extinction coefficient at 1064 nm for desert dust. The advanced multiwavelength Raman polarization lidar was able to provide, for the first time, the lidar ratio (extinction-to-backscatter ratio) and particle linear depolarization ratio at all three classical lidar wavelengths (355, 532 and 1064 nm). The pure dust conditions during the first event exhibit lidar ratios of 47±8, 50±5 and 63±13 sr and particle linear depolarization ratios of 0.260±0.026, 0.298±0.017 and 0.214±0.025 at the wavelengths of 355, 532 and 1064 nm, respectively. The second, slightly polluted dust case shows a similar spectral behavior with values of the lidar ratio of 52±8, 47±5 and 61±10 sr and the depolarization ratio of 0.188±0.053, 0.270±0.017 and 0.242±0.007 at 355, 532 and 1064 nm, respectively. The results were compared to AERONET v3 inversions and GRASP retrievals at six and seven wavelengths, which could reproduce the spectral slope of the lidar ratio from 532 to 1064 nm. The spectral slope of the particle linear depolarization ratio could not be reproduced by the AERONET inversions, especially at 1064 nm.

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Measurements of Saharan dust aerosols over the Eastern Mediterranean using elastic backscatter-Raman lidar, spectrophotometric and satellite observations in the frame of the EARLINET project

Atmospheric Chemistry and Physics ◽

10.5194/acp-5-2065-2005 ◽

2005 ◽

Vol 5 (8) ◽

pp. 2065-2079 ◽

Cited By ~ 140

Author(s):

A. Papayannis ◽

D. Balis ◽

V. Amiridis ◽

G. Chourdakis ◽

G. Tsaknakis ◽

...

Keyword(s):

Eastern Mediterranean ◽

Mean Value ◽

Saharan Dust ◽

Back Trajectory ◽

Air Mass ◽

Mean Values ◽

Dust Aerosols ◽

Back Trajectory Analysis ◽

Spectrophotometric Data ◽

Lidar Ratio

Abstract. We report on the vertical distributions of Saharan dust aerosols over the N.E. Mediterranean region, which were obtained during a typical dust outbreak on August 2000, by two lidar systems located in Athens and Thessaloniki, Greece, in the frame of the European EARLINET project. MODIS and ground sun spectrophotometric data, as well as air-mass backward trajectories confirmed the existence of Saharan dust in the case examined, which was also successfully forecasted by the DREAM dust model. The lidar data analysis for the period 2000-2002 made possible, for the first time, an estimation of the vertical extent of free tropospheric dust layers [mean values of the aerosol backscatter and extinction coefficients and the extinction-to-backscatter ratio (lidar ratio, LR) at 355 nm], as well as a seasonal distribution of Saharan dust outbreaks over Greece, under cloud-free conditions. A mean value of the lidar ratio at 355 nm was obtained over Athens (53±1 sr) and over Thessaloniki (44±2 sr) during the Saharan dust outbreaks. The corresponding aerosol optical thickness (AOT) at 355 nm, in the altitude range 0-5 km, was 0.69±0.12 and 0.65±0.10 for Athens and Thessaloniki, respectively (within the dust layer the AOT was 0.23 and 0.21, respectively). Air-mass back-trajectory analysis performed in the period 2000-2002 for all Saharan dust outbreaks over the N.E. Mediterranean indicated the main pathways followed by the dust aerosols.

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On the spectral depolarisation and lidar ratio of mineral dust provided in the AERONET version 3 inversion product

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-12735-2018 ◽

2018 ◽

Vol 18 (17) ◽

pp. 12735-12746 ◽

Cited By ~ 17

Author(s):

Sung-Kyun Shin ◽

Matthias Tesche ◽

Kwanchul Kim ◽

Maria Kezoudi ◽

Boyan Tatarov ◽

...

Keyword(s):

Great Basin ◽

Mineral Dust ◽

Saharan Dust ◽

General Behaviour ◽

Depolarisation Ratio ◽

Source Regions ◽

Abstract Knowledge ◽

Fine Mode ◽

Lidar Ratio ◽

Lidar Observations

Abstract. Knowledge of the particle lidar ratio (Sλ) and the particle linear depolarisation ratio (δλ) for different aerosol types allows for aerosol typing and aerosol-type separation in lidar measurements. Reference values generally originate from dedicated lidar observations but might also be obtained from the inversion of AErosol RObotic NETwork (AERONET) sun/sky radiometer measurements. This study investigates the consistency of spectral Sλ and δλ provided in the recently released AERONET version 3 inversion product for observations of undiluted mineral dust in the vicinity of the following major deserts: Gobi, Sahara, Arabian, Great Basin, and Great Victoria. Pure dust conditions are identified by an Ångström exponent <0.4 and a fine-mode fraction <0.1. The values of spectral Sλ are found to vary for the different source regions but generally show an increase with decreasing wavelength. The feature correlates to AERONET, retrieving an increase in the imaginary part of the refractive index with decreasing wavelength. The smallest values of Sλ=35–45 sr are found for mineral dust from the Great Basin desert, while the highest values of 50–70 sr have been inferred from AERONET observations of Saharan dust. Values of Sλ at 675, 870, and 1020 nm seem to be in reasonable agreement with available lidar observations, while those at 440 nm are up to 10 sr higher than the lidar reference. The spectrum of δλ shows a maximum of 0.26–0.31 at 1020 nm and decreasing values as wavelength decreases. AERONET-derived δλ values at 870 and 1020 nm are in line with the lidar reference, while values of 0.19–0.24 at 440 nm are smaller than the independent lidar observations by a difference of 0.03 to 0.08. This general behaviour is consistent with earlier studies based on AERONET version 2 products.

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First triple-wavelength lidar observations of depolarization and extinction-to-backscatter ratios of Saharan dust

Atmospheric Chemistry and Physics ◽

10.5194/acp-22-355-2022 ◽

2022 ◽

Vol 22 (1) ◽

pp. 355-369

Author(s):

Moritz Haarig ◽

Albert Ansmann ◽

Ronny Engelmann ◽

Holger Baars ◽

Carlos Toledano ◽

...

Keyword(s):

Wavelength Dependence ◽

Saharan Dust ◽

Depolarization Ratio ◽

Shape Model ◽

Lidar Measurements ◽

Fine Mode ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

Dust Case ◽

Lidar Observations

Abstract. Two layers of Saharan dust observed over Leipzig, Germany, in February and March 2021 were used to provide the first-ever lidar measurements of the dust lidar ratio (extinction-to-backscatter ratio) and linear depolarization ratio at all three classical lidar wavelengths (355, 532 and 1064 nm). The pure-dust conditions during the first event exhibit lidar ratios of 47 ± 8, 50 ± 5 and 69 ± 14 sr and particle linear depolarization ratios of 0.242 ± 0.024, 0.299 ± 0.018 and 0.206 ± 0.010 at wavelengths of 355, 532 and 1064 nm, respectively. The second, slightly polluted-dust case shows a similar spectral behavior of the lidar and depolarization ratio with values of the lidar ratio of 49 ± 4, 46 ± 5 and 57 ± 9 sr and the depolarization ratio of 0.174 ± 0.041, 0.298 ± 0.016 and 0.242 ± 0.007 at 355, 532 and 1064 nm, respectively. The results were compared with Aerosol Robotic Network (AERONET) version 3 (v3) inversion solutions and the Generalized Retrieval of Aerosol and Surface Properties (GRASP) at six and seven wavelengths. Both retrieval schemes make use of a spheroid shape model for mineral dust. The spectral slope of the lidar ratio from 532 to 1064 nm could be well reproduced by the AERONET and GRASP retrieval schemes. Higher lidar ratios in the UV were retrieved by AERONET and GRASP. The enhancement was probably caused by the influence of fine-mode pollution particles in the boundary layer which are included in the columnar photometer measurements. Significant differences between the measured and retrieved wavelength dependence of the particle linear depolarization ratio were found. The potential sources for these uncertainties are discussed.

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Measurements of Saharan dust aerosols over the Eastern Mediterranean using elastic backscatter-Raman lidar, spectrophotometric and satellite observations in the frame of the EARLINET project

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-5-2075-2005 ◽

2005 ◽

Vol 5 (2) ◽

pp. 2075-2110 ◽

Cited By ~ 4

Author(s):

A. Papayannis ◽

D. Balis ◽

V. Amiridis ◽

G. Chourdakis ◽

G. Tsaknakis ◽

...

Keyword(s):

Eastern Mediterranean ◽

Mean Value ◽

Saharan Dust ◽

Back Trajectory ◽

Air Mass ◽

Mean Values ◽

Dust Aerosols ◽

Back Trajectory Analysis ◽

Spectrophotometric Data ◽

Lidar Ratio

Abstract. We report on the vertical distributions of Saharan dust aerosols over the N.E. Mediterranean region, which were obtained during a typical dust outbreak on August 2000, by two lidar systems located in Athens and Thessaloniki, Greece, in the frame of the European EARLINET project. MODIS and ground sun spectrophotometric data, as well as air-mass backward trajectories confirmed the existence of Saharan dust in the case examined, which was also successfully forecasted by the DREAM dust model. The lidar data analysis for the period 2000–2002 made possible, for the first time, an estimation of the vertical extent of free tropospheric dust layers (mean values of the aerosol backscatter and extinction coefficients and the extinction-to-backscatter ratio (lidar ratio, LR) at 355 nm), as well as a seasonal distribution of Saharan dust outbreaks over Greece, under cloud-free conditions. A mean value of the lidar ratio at 355 nm was obtained over Athens (52.81±1.02 sr) and over Thessaloniki (44.19±1.72 sr) during the Saharan dust outbreaks. The corresponding aerosol optical thickness (AOT) at 355 nm, in the altitude range 0–5 km, was 0.69±0.12 and 0.65±0.10 for Athens and Thessaloniki, respectively (within the dust layer the AOT was 0.23 and 0.21, respectively). Air-mass back-trajectory analysis performed in the period 2000–2002 for all Saharan dust outbreaks over the N. E. Mediterranean indicated the main pathways followed by the dust aerosols.

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Dust Lidar Ratios Retrieved from the CALIOP Measurements Using the MODIS AOD as a Constraint

Remote Sensing ◽

10.3390/rs12020251 ◽

2020 ◽

Vol 12 (2) ◽

pp. 251 ◽

Cited By ~ 2

Author(s):

Man-Hae Kim ◽

Sang-Woo Kim ◽

Ali H. Omar

Keyword(s):

Saharan Dust ◽

Orthogonal Polarization ◽

Dust Aerosols ◽

Deep Blue ◽

Source Regions ◽

Modis Aod ◽

Moderate Resolution ◽

Lidar Ratio ◽

Resolution Imaging ◽

Moderate Resolution Imaging Spectroradiometer

Lidar ratio for dust aerosols is retrieved from a synergetic use of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Total Attenuated Backscatter coefficients and the Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depths (AODs) for 5 years from 2007 to 2011. MODIS AODs from the Dark Target (DT) algorithm over ocean and from the Deep Blue (DB) algorithm over land are used as a constraint for the retrieval. The dust lidar ratio is retrieved larger over land (46.6 ± 36.3 sr) than ocean (39.5 ± 16.8 sr) and shows distinct regional variation. Lidar ratio for Saharan dust (49.5 ± 36.8 sr) is larger than Arabian dust (42.5 ± 26.2 sr). Lidar ratios for dust aerosols transported to Mediterranean Sea (44.4 ± 15.9 sr), Mid Atlantic (40.3 ± 12.4 sr), and Arabian Sea (37.5 ± 12.1 sr) show lower values relative to their source regions. Retrieved dust lidar ratios for Taklamakan and Gobi Deserts region (35.0 ± 31.1 sr) and Australia (35.4 ± 34.4 sr) are slightly lower than the above-mentioned regions. AOD comparison between CALIOP and MODIS shows that the CALIOP AOD is biased low. When including clear air AOD for CALIOP, however, AODs from two sensors become more comparable.

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Evaluation of the Lidar/Radiometer Inversion Code (LIRIC) to determine microphysical properties of volcanic and desert dust

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-6-911-2013 ◽

2013 ◽

Vol 6 (1) ◽

pp. 911-948 ◽

Cited By ~ 4

Author(s):

J. Wagner ◽

A. Ansmann ◽

U. Wandinger ◽

P. Seifert ◽

A. Schwarz ◽

...

Keyword(s):

Theoretical Background ◽

Saharan Dust ◽

Dust Particles ◽

Raman Lidar ◽

Particle Volume ◽

Microphysical Properties ◽

Fine Mode ◽

Lidar Ratio ◽

Lidar Observations ◽

Good Agreement

Abstract. The Lidar/Radiometer Inversion Code (LIRIC) combines the multiwavelength lidar technique with sun-sky photometry and allows us to retrieve vertical profiles of particle optical and microphysical properties, separately for fine-mode and coarse-mode particles. After a brief presentation of the theoretical background, we evaluate the potential of LIRIC to retrieve the optical and microphysical properties of irregularly shaped dust particles. The method is applied to two very different aerosol scenarios, a strong Saharan dust outbreak towards central Europe and an Eyjafjallajökull volcanic dust event. LIRIC profiles of particle volume and mass concentrations are compared with results obtained with the polarization-lidar-based POLIPHON method. LIRIC profiles of optical properties such as particle backscatter coefficients, lidar ratio, Ångström exponent, and particle depolarization ratio are compared with direct Raman lidar observations. Good agreement between the different results are found for most of the retrieval products.

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