Lidar is a reliable tool for active remote sensing detection of atmospheric aerosols. A multi-wavelength aerosol lidar (MWAL) with 355 nm, 532 and 1064 nm as detection light sources has been ...developed and deployed for operational observations at Haidian District Meteorological Service of Beijing. The structure design, specifications, observation campaign, and detection principle of the MWAL are introduced. To ensure the accuracy and reliability of the lidar observation data, the calibration contents, and methods of lidar are proposed, including the correction, and gluing of the original data, the collimation of the transmitting and receiving optical axes, the testing of signal saturation, the correction of molecular Rayleigh fitting and the determination of the depolarization ratio correction factor. Finally, a haze process from 29 September to 2 October 2019 was observed and analyzed using the data of lidar, digital radiosonde, air quality and relative humidity observed by the Haidian District Meteorological Service. The detection results show the reliability of lidar which can effectively obtain the temporal and spatial variation characteristics of the haze. The profiles of aerosol extinction coefficient, potential temperature and relative humidity can be effectively used to analyze the haze thickness and the influence of relative humidity on aerosol particles. The data of air quality monitor shows that PM
10
is the main pollutant and the ratio of PM
2.5
/PM
10
is negatively correlated with relative humidity. Finally, the HYSPLIT trajectory tracking model of the National Oceanic and Atmospheric Administration (NOAA) is used to further study the source of pollutants in this haze process.
Here, we investigate the annual variations of particulate matter (PM) levels for Tehran megacity during 2018, using ground-based measurements and remotely sensed data, taken from CALIOP space-borne ...lidar and MODIS-Aqua sensor. Furthermore, the aerosol types of Tehran are determined against three other megacities, namely Delhi, Helsinki and Calgary. Satellite data attest the dust/polluted dust as the dominant aerosol types in Tehran during warm/cold seasons, respectively. The values of particulate depolarization ratio (PDR), particulate color ratio (PCR) and aerosol optical depth (AOD) are calculated along the CALIPSO satellite night-time trajectories over Tehran. This demonstrates that the maximums of PDR and PCR occur during July. The seasonal analyses of vertically averaged PDR and PCR attest that the maximum values take place during summer time, while minimum records belong to the fall season. The correlation analysis emphasizes a sensible conformity between column AOD data (retrieved from MODIS-Aqua sensor) and the PM2.5 concentrations (acquired from ground-based meteorological stations). Besides, PDR is inversely correlated to relative humidity. In this study, the origins of pollutants are envisaged based on PSCF and frequency analysis of back-trajectories for February and July 2018, indicating the main origin of dust arises from Turkmenistan deserts in summer and Iraq/western Iran arid areas during winter.
•PM conditions are investigated in Tehran/Iran.•Dust/polluted dust are dominant aerosol types in summer/winter times.•Max/Min of PDR and PCR takes place during summer/fall season.•Dust aerosols are transported from Turkmenistan to Tehran in summer.•Dust aerosols are migrated from Iraq to Tehran in winter.
•The degree of linear polarization is sensitive to the coating material.•The depolarization ratio at backscatering direction is sensitive to changes in particle size.•Changes in the degree of linear ...polarization are in accordance with the Umov law.
In this article, we study the impact of water coating on light scattering by irregularly shaped agglomerated debris particles. We compute light-scattering properties of three types of irregular particles, which simulate atmospheric particles before and after coating. We consider two types of the Junge size distributions over sub-micron range of rc. The coating is represented as deposition of same volume of material on original particles. We found that only the degree of linear polarization is sensitive to coating type, especially maximum value of the polarization that is typically acquired at side scattering. Behavior of the degree of linear polarization maximum appears in accordance with the Umov effect. The linear depolarization ratio at backscattering direction δl is insensitive to coating material, but it is dependent from particles size.
Recently, there has been increasing interest to derive the fractions of fine- and coarse-mode dust particles from polarization lidar measurements. For this, assumptions of the backscattering ...properties of the complex dust particles have to be made either by using empirical data or particle models. Laboratory measurements of dust backscattering properties are important to validate the assumptions made in the lidar retrievals and to estimate their uncertainties. Here, we present laboratory measurements of linear and circular near-backscattering (178°) depolarization ratios of over 200 dust samples measured at 488 and 552nm wavelengths. The measured linear depolarization ratios ranged from 0.03 to 0.36 and were strongly dependent on the particle size. The strongest size-dependence was observed for fine-mode particles as their depolarization ratios increased almost linearly with particle median diameter from 0.03 to 0.3, whereas the coarse-mode particle depolarization values stayed rather constant with a mean linear depolarization ratio of 0.27. The depolarization ratios were found to be insensitive to the dust source region or thin coating of the particles or to changes in relative humidity. We compared the measurements with results of three different scattering models. With certain assumptions for model particle shape, all the models were capable of correctly describing the size-dependence of the measured dust particle, albeit the model particles significantly differed in composition, shape and degree of complexity. Our results show potential for distinguishing the dust fine- and coarse-mode distributions based on their depolarization properties and, thus, can serve the lidar community as an empirical reference.
The Wind Velocity Radar Nephoscope (WIVERN) mission, one of the four ESA Earth Explorer 11 candidate missions, aims at globally observing, for the first time, simultaneously vertical profiles of ...reflectivities and line-of-sight (LOS) winds in cloudy and precipitating regions. WIVERN adopts a dual-polarization Doppler radar to overcome the short decorrelation time between successive radar pulses transmitted from low Earth-orbiting satellites with finite beamwidth antennas. WIVERN transmits a single polarization state at a time (H or V), receives in both the polarization states, and uses the polarization diversity pulse pair (PDPP) technique to estimate the Doppler velocity. The weaker cross-polar signals can sometimes interfere with the copolar ones, causing ghost signals in the measurements that hinder the system's overall performance. In addition, with the envisaged radar trigger mode, parameters such as linear depolarization ratio (LDR) and differential reflectivity (<inline-formula> <tex-math notation="LaTeX">Z_{\text {DR}} </tex-math></inline-formula>) cannot be directly measured because of the nearly simultaneous transmission of H and V pulses. To overcome these challenges, this article presents a novel technique based on the optimal estimation (OE) algorithm for retrieving LDR, <inline-formula> <tex-math notation="LaTeX">Z_{\text {DR}} </tex-math></inline-formula>, and copolar reflectivity for radars operated in the PDPP mode. The performance of the proposed method is evaluated using a realistic climatology of profiles simulated from CloudSat data. Results demonstrate that copolar reflectivity can be accurately retrieved in regions with a good signal-to-noise ratio (SNR) and in the absence of simultaneous crosstalk interference in both the channels (which occurs very rarely). The LDR retrieval, on the other hand, is typically driven by the a priori with a substantial impact of measurements only for the surface returns. The impact of crosstalk is also assessed on the reduction of precise Doppler measurements. Findings confirm that a selection of the separation between the two polarization diversity pulses (<inline-formula> <tex-math notation="LaTeX">T_{\text {HV}} </tex-math></inline-formula>) of <inline-formula> <tex-math notation="LaTeX">20 \mu \text{s} </tex-math></inline-formula> achieves a good balance between the large errors originated by the strong dependence on the Doppler phase noise at small <inline-formula> <tex-math notation="LaTeX">T_{\text {HV}}\text{s} </tex-math></inline-formula> and those caused by the drop in correlation and unambiguous Nyquist velocity at large <inline-formula> <tex-math notation="LaTeX">T_{\text {HV}} </tex-math></inline-formula>.
Five years of CALIPSO lidar layer products are used to study transpacific transport of Asian dust. We focus on possible changes to dust intrinsic optical properties during the course of transport, ...with specific emphasis on changes to particulate depolarization ratio (PDR). PDR distributions for Asian dust transported across the Pacific are compared to previously reported PDR distributions for African dust transported across the Atlantic. African dust shows a slight decreasing trend in PDR during westward transport across the Atlantic during its most active long-range transport season in summer. Asian dust, on the other hand, shows some spatial variability in PDR over the Pacific during its most active long-range transport season in spring. The dust PDR is generally smaller over the ocean than over the Tarim basin and nearby downwind regions. PDR also shows a decreasing trend with latitude moving northward toward the Arctic, together with an increasing trend in the dust aerosol optical depth (AOD) when passing over polluted Asian regions. Possible explanations include (i) the mixing of dust externally or internally with other types of aerosol over the heavily developed industrial regions in East Asia, and (ii) the downstream mixing of dust plumes from different source regions (i.e., Tarim and Gobi). Dust from different source regions exhibits relatively large differences in PDR, with mean values of 0.34±0.07, 0.28±0.06, and 0.30±0.08, respectively, over the Tarim basin, Gobi Desert and Northwest African source regions. Different transport mechanisms are seen for African dust and Asian dust. Asian dust transport is originated by cold fronts and driven by westerly jets. In contrast, summer African transatlantic dust transport is driven by trade winds and is generally well confined in altitude in the free troposphere throughout the tropics and subtropics.
► More spatial variability in Asian dust PDR during transpacific transport. ► Largely unchanged African dust PDR during transatlantic transport in summer. ► Relatively large differences in pure dust PDR in different sources.
The aerosol color ratio, depolarization ratio and aerosol optical depth (AOD) were measured by a two-wavelength-depolarization lidar at Wuhan, China during the period from May 2015–July 2016. The ...annual average AOD at Wuhan was about 0.33 during the period 2015–2016. The seasonal average AOD is small (0.26 ± 0.25) during the winter (December–February) season and large (0.4 ± 0.1) during the summer (June–August) season. The monthly average color ratio is small (0.23 ± 0.09) in January and large (0.76 ± 0.21) in August with an annual average value 0.54. The maximum monthly mean depolarization ratio (0.2 ± 0.07) occurred in the month of October, while the minimum (0.06 ± 0.02) occurred in the month of September, and the annual mean depolarization ratio was about 0.17. An analysis of temporal variations of color ratio and depolarization ratio suggests the presence of coarse and non-spherical particles during the autumn. The aerosol color ratio between 0.3 and 2.0 km was large (0.65), suggesting a large number of coarse particles in this range. The vertical distribution of the depolarization ratio is uniform. Finally, the spatial aerosol distribution under different weather conditions and its relationship with the color ratio is investigated in detail. The color ratio value of 0.74 could be used as a threshold for distinguishing polluted weather from clean weather. The aerosol optical and physical properties are investigated to provide a comprehensive understanding of aerosol radiative forcing and environmental problems in this region.
•Aerosol shape and size over urban Central China is investigated firstly.•Distribution of irregular particles is uniformly distributed over the vertical structure.•Color ratio could be used as a threshold for distinguishing polluted aerosol.
Optimizing CALIPSO Saharan dust retrievals Amiridis, V; Wandinger, U; Marinou, E ...
Atmospheric chemistry and physics,
12/2013, Letnik:
13, Številka:
23
Journal Article, Publication
Recenzirano
Odprti dostop
We demonstrate improvements in CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations) dust extinction retrievals over northern Africa and Europe when corrections are applied ...regarding the Saharan dust lidar ratio assumption, the separation of the dust portion in detected dust mixtures, and the averaging scheme introduced in the Level 3 CALIPSO product. First, a universal, spatially constant lidar ratio of 58 sr instead of 40 sr is applied to individual Level 2 dust-related backscatter products. The resulting aerosol optical depths show an improvement compared with synchronous and collocated AERONET (Aerosol Robotic Network) measurements. An absolute bias of the order of −0.03 has been found, improving on the statistically significant biases of the order of −0.10 reported in the literature for the original CALIPSO product. When compared with the MODIS (Moderate-Resolution Imaging Spectroradiometer) collocated aerosol optical depth (AOD) product, the CALIPSO negative bias is even less for the lidar ratio of 58 sr. After introducing the new lidar ratio for the domain studied, we examine potential improvements to the climatological CALIPSO Level 3 extinction product: (1) by introducing a new methodology for the calculation of pure dust extinction from dust mixtures and (2) by applying an averaging scheme that includes zero extinction values for the nondust aerosol types detected. The scheme is applied at a horizontal spatial resolution of 1° × 1° for ease of comparison with the instantaneous and collocated dust extinction profiles simulated by the BSC-DREAM8b dust model. Comparisons show that the extinction profiles retrieved with the proposed methodology reproduce the well-known model biases per subregion examined. The very good agreement of the proposed CALIPSO extinction product with respect to AERONET, MODIS and the BSC-DREAM8b dust model makes this dataset an ideal candidate for the provision of an accurate and robust multiyear dust climatology over northern Africa and Europe.
We present results of the vertical distribution variation of volcanic aerosol layers in the upper troposphere and lower stratosphere. The data were taken with our multiwavelength aerosol Raman lidar ...at Gwangju (35.10° N, 126.53° E), Korea. The volcanic ash particles and gases were released around 12 June 2011 during the eruption of the Nabro volcano (13.37° N, 41.7° E) in Eritrea, east Africa. Forward trajectory computations show that the volcanic aerosols were advected from North Africa to East Asia. The first measurement of the aerosol layer over Korea was on 19 June 2011. The aerosol layers appeared between 15 km and 17 km height asl (above sea level). The maximum value of the aerosol layer of the particle backscatter coefficient (1.5 ± 0.3 Mm−1 sr−1) and the linear particle depolarization ratio at 532 nm (2.2%) were observed at 16.4 km height asl. We continuously probed the upper troposphere and lower stratosphere for this volcanic aerosol layer during the following 6 months, until December 2011. The volcanic aerosol layer showed a single-peak of the particle backscatter coefficient and a comparably narrow vertical thickness at our observation site at the beginning of our observation period (i.e. comparably soon after the initial eruption period). After that initial period the vertical distribution of the plume changed. Multiple peaks and a comparably broad geometrical thickness developed with progressing observation time. The vertical thickness of the volcanic aerosol layer expanded up to 10 km by 3 August 2011. The linear particle depolarization ratios were larger in the lower part of the aerosol layer than the upper part of the aerosol layer. We observed a strong variation of the AOD (aerosol optical depth) in the first two months of our lidar observations. After these two months the AOD gradually decreased with time from September to December 20111 and the maximum particle backscatter coefficients consistently decreased. The corresponding e-folding decay time of the layer AOD was 117 days.
•The volcanic aerosol layer in the stratosphere was observed using lidar.•The aerosol layer show different vertical profiles and optical properties with time.•Non-spherical particle is more favorable to gravitational sedimentation.•An e-folding decay time of the layer is 117 days.
While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. ...To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen.
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