scholarly journals Statistics of Cloud Optical Properties from Airborne Lidar Measurements

2011 ◽  
Vol 28 (7) ◽  
pp. 869-883 ◽  
Author(s):  
John E. Yorks ◽  
Dennis L. Hlavka ◽  
William D. Hart ◽  
Matthew J. McGill
Keyword(s):  
Optical Properties ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Transmission Loss ◽  
Geographic Location ◽  
Airborne Lidar ◽  
Optical Parameters ◽  
Depolarization Ratio ◽  
Ice Clouds ◽  
Lidar Ratio

Abstract Accurate knowledge of cloud optical properties, such as extinction-to-backscatter ratio and depolarization ratio, can have a significant impact on the quality of cloud extinction retrievals from lidar systems because parameterizations of these variables are often used in nonideal conditions to determine cloud phase and optical depth. Statistics and trends of these optical parameters are analyzed for 4 yr (2003–07) of cloud physics lidar data during five projects that occurred in varying geographic locations and meteorological seasons. Extinction-to-backscatter ratios (also called lidar ratios) are derived at 532 nm by calculating the transmission loss through the cloud layer and then applying it to the attenuated backscatter profile in the layer, while volume depolarization ratios are computed using the ratio of the parallel and perpendicular polarized 1064-nm channels. The majority of the cloud layers yields a lidar ratio between 10 and 40 sr, with the lidar ratio frequency distribution centered at 25 sr for ice clouds and 16 sr for altocumulus clouds. On average, for ice clouds the lidar ratio slightly decreases with decreasing temperature, while the volume depolarization ratio increases significantly as temperatures decrease. Trends for liquid water clouds (altocumulus clouds) are also observed. Ultimately, these observed trends in optical properties, as functions of temperature and geographic location, should help to improve current parameterizations of extinction-to-backscatter ratio, which in turn should yield increased accuracy in cloud optical depth and radiative forcing estimates.

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 Radiative forcing of the desert aerosol at Ouarzazate (Morocco)

2018 ◽  
Vol 37 ◽  
pp. 03004
Author(s):  
Abdelouahid Tahiri ◽  
Mohamed Diouri
Keyword(s):  
Optical Properties ◽  
Atmospheric Aerosol ◽  
Radiative Forcing ◽  
Cloud Formation ◽  
Optical Parameters ◽  
Aerosol Radiative Forcing ◽  
Daily Average ◽  
Definition Of ◽  
Aerosol Radiative

The atmospheric aerosol contributes to the definition of the climate with direct effect, the diffusion and absorption of solar and terrestrial radiations, and indirect, the cloud formation process where aerosols behave as condensation nuclei and alter the optical properties. Satellites and ground-based networks (solar photometers) allow the terrestrial aerosol observation and the determination of impact. Desert aerosol considered among the main types of tropospheric aerosols whose optical property uncertainties are still quite important. The analysis concerns the optical parameters recorded in 2015 at Ouarzazate solar photometric station (AERONET/PHOTONS network, http://aeronet.gsfc.nasa.gov/) close to Saharan zone. The daily average aerosol optical depthτaer at 0.5μm, are relatively high in summer and less degree in spring (from 0.01 to 1.82). Daily average of the Angstrom coefficients α vary between 0.01 and 1.55. The daily average of aerosol radiative forcing at the surface range between -150W/m2 and -10 W/m2 with peaks recorded in summer, characterized locally by large loads of desert aerosol in agreement with the advections of the Southeast of Morocco. Those recorded at the Top of the atmosphere show a variation from -74 W/m2 to +24 W/m2

scholarly journals Lalinet status - station expansion and lidar ratio systematic measurements

2018 ◽  
Vol 176 ◽  
pp. 09002
Author(s):  
Eduardo Landulfo ◽  
Fabio Lopes ◽  
Gregori Arruda Moreira ◽  
Jonatan da Silva ◽  
Pablo Ristori ◽  
...  
Keyword(s):  
Optical Properties ◽  
Radiation Transfer ◽  
Optical Parameters ◽  
Aerosol Optical Properties ◽  
The North ◽  
Circulation Patterns ◽  
Spatial Coverage ◽  
Ratio Data ◽  
Lidar Ratio ◽  
Transfer Models

LALINET is expanding regionally to guarantee spatial coverage over South and Central Americas. One of the network goals is to obtain a set of regional representative aerosol optical properties such as particle backscatter, extinction and lidar ratio. Given the North-South extension and influence of distinct airmass circulation patterns it is paramount to distinguish these optical parameters in order to gain better perfomance in radiation transfer models. A set of lidar ratio data is presented.

scholarly journals Extinction and optical depth retrievals for CALIPSO's Version 4 data release

2018 ◽  
Vol 11 (10) ◽  
pp. 5701-5727 ◽  
Author(s):  
Stuart A. Young ◽  
Mark A. Vaughan ◽  
Anne Garnier ◽  
Jason L. Tackett ◽  
James D. Lambeth ◽  
...  
Keyword(s):  
Optical Depth ◽  
Satellite Observations ◽  
Orthogonal Polarization ◽  
Ice Clouds ◽  
Extinction Coefficients ◽  
Retrieval Algorithms ◽  
Data Release ◽  
Data Products ◽  
Lidar Ratio ◽  
Level 2

Abstract. The Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been making near-global height-resolved measurements of cloud and aerosol layers since mid-June 2006. Version 4.10 (V4) of the CALIOP data products, released in November 2016, introduces extensive upgrades to the algorithms used to retrieve the spatial and optical properties of these layers, and thus there are both obvious and subtle differences between V4 and previous data releases. This paper describes the improvements made to the extinction retrieval algorithms and illustrates the impacts of these changes on the extinction and optical depth estimates reported in the CALIPSO lidar level 2 data products. The lidar ratios for both aerosols and ice clouds are generally higher than in previous data releases, resulting in generally higher extinction coefficients and optical depths in V4. A newly implemented algorithm for retrieving extinction coefficients in opaque layers is described and its impact examined. Precise lidar ratio estimates are also retrieved in these opaque layers. For semi-transparent cirrus clouds, comparisons between CALIOP V4 optical depths and the optical depths reported by MODIS collection 6 show substantial improvements relative to earlier comparisons between CALIOP version 3 and MODIS collection 5.

scholarly journals Analysis of a warehouse fire smoke plume over Paris with an N<sub>2</sub> Raman lidar and an optical thickness matching algorithm

2018 ◽  
Vol 11 (12) ◽  
pp. 6525-6538 ◽  
Author(s):  
Xiaoxia Shang ◽  
Patrick Chazette ◽  
Julien Totems
Keyword(s):  
Optical Thickness ◽  
Monte Carlo Algorithm ◽  
Optical Parameters ◽  
Depolarization Ratio ◽  
Raman Lidar ◽  
Smoke Plume ◽  
Paris Area ◽  
Fire Smoke ◽  
Lidar Ratio ◽  
Warehouse Fire

Abstract. A smoke plume, coming from an accidental fire in a textile warehouse in the north of Paris, covered a significant part of the Paris area on 17 April 2015 and seriously impacted the visibility over the megalopolis. This exceptional event was sampled with an automatic N2 Raman lidar, which operated 15 km south of Paris. The industrial pollution episode was concomitant with the long-range transport of dust aerosols originated from the Sahara, and with the presence of an extended stratus cloud cover. The analysis of the ground-based lidar profiles therefore required the development of an original inversion algorithm, using a top-down aerosol optical thickness matching (TDAM) approach. This study is, to the best of our knowledge, the first lidar measurement of a fresh smoke plume, emitted only a few hours after an accidental warehouse fire. Vertical profiles of the aerosol extinction coefficient, depolarization ratio, and lidar ratio are derived to optically characterize the aerosols that form the plume. We found a lidar ratio close to 50±10 sr for this fire smoke aerosol layer. The particle depolarization ratio is low, ∼1±0.1 %, suggesting the presence of either small particles or spherical hydrated aerosols in that layer. A Monte Carlo algorithm was used to assess the uncertainties on the optical parameters and to evaluate the TDAM algorithm.

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 Characterization of the Far Infrared Properties and Radiative Forcing of Antarctic Ice and Water Clouds Exploiting the Spectrometer-LiDAR Synergy

2020 ◽  
Vol 12 (21) ◽  
pp. 3574
Author(s):  
Gianluca Di Natale ◽  
Giovanni Bianchini ◽  
Massimo Del Guasta ◽  
Marco Ridolfi ◽  
Tiziano Maestri ◽  
...  
Keyword(s):  
Optical Depth ◽  
Radiative Forcing ◽  
Learning Algorithm ◽  
Droplet Diameter ◽  
Far Infrared ◽  
Base Station ◽  
Effective Diameter ◽  
Liquid Water Path ◽  
Ice Clouds ◽  
Cloud Optical Depth

Optical and microphysical cloud properties are retrieved from measurements acquired in 2013 and 2014 at the Concordia base station in the Antarctic Plateau. Two sensors are used synergistically: a Fourier transform spectroradiometer named REFIR-PAD (Radiation Explorer in Far Infrared-Prototype for Applications and Developments) and a backscattering-depolarization LiDAR. First, in order to identify the cloudy scenes and assess the cloud thermodynamic phase, the REFIR-PAD spectral radiances are ingested by a machine learning algorithm called Cloud Identification and Classification (CIC). For each of the identified cloudy scenes, the nearest (in time) LiDAR backscattering profile is processed by the Polar Threshold (PT) algorithm that allows derivation of the cloud top and bottom heights. Subsequently, using the CIC and PT results as external constraints, the Simultaneous Atmospheric and Clouds Retrieval (SACR) code is applied to the REFIR-PAD spectral radiances. SACR simultaneously retrieves cloud optical depth and effective dimensions and atmospheric vertical profiles of water vapor and temperature. The analysis determines an average effective diameter of 28 μm with an optical depth of 0.76 for the ice clouds. Water clouds are only detected during the austral Summer, and the retrieved properties provide an average droplet diameter of 9 μm and average optical depth equal to four. The estimated retrieval error is about 1% for the ice crystal/droplet size and 2% for the cloud optical depth. The sensitivity of the retrieved parameters to the assumed crystal shape is also assessed. New parametrizations of the optical depth and the longwave downwelling forcing for Antarctic ice and water clouds, as a function of the ice/liquid water path, are presented. The longwave downwelling flux, computed from the top of the atmosphere to the surface, ranges between 70 and 220 W/m2. The estimated cloud longwave forcing at the surface is (31 ± 7) W/m2 and (29 ± 6) W/m2 for ice clouds and (64 ± 12) and (62 ± 11) W/m2 for water clouds, in 2013 and 2014, respectively. The total average cloud forcing for the two years investigated is (46 ± 9) W/m2.

scholarly journals Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

2011 ◽  
Vol 11 (7) ◽  
pp. 20181-20201 ◽  
Author(s):  
D. Kim ◽  
M. Chin ◽  
H. Yu ◽  
T. F. Eck ◽  
A. Sinyuk ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
North Africa ◽  
Radiative Forcing ◽  
Arabian Peninsula ◽  
Single Scattering ◽  
Major Fraction ◽  
Remote Sensing Techniques

Abstract. Dust optical properties over North Africa and the Arabian Peninsula are extracted from the quality assured multi-year datasets obtained at 14 sites of the Aerosol Robotic Network (AERONET). We select the data with (a) large aerosol optical depth (AOD ≥ 0.4 at 440 nm) and (b) small Ångström exponent (Åext ≤ 0.2) for retaining high accuracy and reducing interference of non-dust aerosols. The result indicates that the major fraction of high aerosol optical depth days are dominated by dust over these sites even though it varies depending on location and time. We have found that the annual mean and standard deviation of single scattering albedo, asymmetry parameter, real refractive index, and imaginary refractive index for Saharan and Arabian desert dust is 0.946 ± 0.005, 0.752 ± 0.014, 1.498 ± 0.032, and 0.0025 ± 0.0036 at 550 nm wavelength, respectively. Dust aerosol selected by this method is less absorbing than the previously reported values over these sites. The weaker absorption of dust from this study is consistent with the previously studies using remote sensing techniques. These results can help to constrain uncertainties in estimating global dust shortwave radiative forcing.

scholarly journals Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

2011 ◽  
Vol 11 (20) ◽  
pp. 10733-10741 ◽  
Author(s):  
D. Kim ◽  
M. Chin ◽  
H. Yu ◽  
T. F. Eck ◽  
A. Sinyuk ◽  
...  
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
North Africa ◽  
Radiative Forcing ◽  
Arabian Peninsula ◽  
Single Scattering ◽  
Major Fraction ◽  
Remote Sensing Techniques

Abstract. Dust optical properties over North Africa and the Arabian Peninsula are extracted from the quality assured multi-year datasets obtained at 14 sites of the Aerosol Robotic Network (AERONET). We select the data with (a) large aerosol optical depth (AOD ≥ 0.4 at 440 nm) and (b) small Ångström exponent (Åext ≤ 0.2) for retaining high accuracy and reducing interference of non-dust aerosols. The result indicates that the major fraction of high aerosol optical depth days are dominated by dust over these sites even though it varies depending on location and time. We have found that the annual mean and standard deviation of single scattering albedo, asymmetry parameter, real refractive index, and imaginary refractive index for Saharan and Arabian desert dust is 0.944 ± 0.005, 0.752 ± 0.014, 1.498 ± 0.032, and 0.0024 ± 0.0034 at 550 nm wavelength, respectively. Dust aerosol selected by this method is less absorbing than the previously reported values over these sites. The weaker absorption of dust from this study is consistent with the studies using remote sensing techniques from satellite. These results can help to constrain uncertainties in estimating global dust shortwave radiative forcing.

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.

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