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Journal ArticleDOI

3+2 + X : what is the most useful depolarization input for retrieving microphysical properties of non-spherical particles from lidar measurements using the spheroid model of Dubovik et al. (2006)?

TL;DR: In this paper, the effect of including the particle linear depolarization ratio (λDR) as a third input parameter for the inversion of lidar data was investigated, and it was shown that δ355 gives a spheroid fraction that closely resembles the dust ratio obtained from using β532 and δ532 in a methodology applied in aerosol-type separation.
Abstract: . The typical multiwavelength aerosol lidar data set for inversion of optical to microphysical parameters is composed of three backscatter coefficients ( β ) at 355, 532, and 1064 nm and two extinction coefficients ( α ) at 355 and 532 nm. This data combination is referred to as a 3β+2α or 3+2 data set. This set of data is sufficient for retrieving some important microphysical particle parameters if the particles have spherical shape. Here, we investigate the effect of including the particle linear depolarization ratio ( δ ) as a third input parameter for the inversion of lidar data. The inversion algorithm is generally not used if measurements show values of δ that exceed 0.10 at 532 nm, i.e. in the presence of non-spherical particles such as desert dust, volcanic ash, and, under special circumstances, biomass-burning smoke. We use experimental data collected with instruments that are capable of measuring δ at all three lidar wavelengths with an inversion routine that applies the spheroidal light-scattering model of Dubovik et al. ( 2006 ) with a fixed axis-ratio distribution to replicate scattering properties of non-spherical particles. The inversion gives the fraction of spheroids required to replicate the optical data as an additional output parameter. This is the first systematic test of the effect of using all theoretically possible combinations of δ taken at 355, 532, and 1064 nm as input in the lidar data inversion. We find that depolarization information of at least one wavelength already provides useful information for the inversion of optical data that have been collected in the presence of non-spherical mineral dust particles. However, any choice of δλ will give lower values of the single-scattering albedo than the traditional 3+2 data set. We find that input data sets that include δ355 give a spheroid fraction that closely resembles the dust ratio we obtain from using β532 and δ532 in a methodology applied in aerosol-type separation. The use of δ355 in data sets of two or three δλ reduces the spheroid fraction that is retrieved when using δ532 and δ1064 . Use of the latter two parameters without accounting for δ355 generally leads to high spheroid fractions that we consider not trustworthy. The use of three δλ instead of two δλ , including the constraint that one of these is measured at 355 nm does not provide any advantage over using 3 + 2 + δ 355 for the observations with varying contributions of mineral dust considered here. However, additional measurements at wavelengths different from 355 nm would be desirable for application to a wider range of aerosol scenarios that may include non-spherical smoke particles, which can have values of δ355 that are indistinguishable from those found for mineral dust. We therefore conclude that – depending on measurement capability – the future standard input for inversion of lidar data taken in the presence of mineral dust particles and using the spheroid model of Dubovik et al. ( 2006 ) might be 3 + 2 + δ 355 or 3 + 2 + δ 355 + δ 532 .

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Citations
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01 Jan 2010
TL;DR: In this article, the authors used Tikhonov's inversion with regularization and made use of kernel functions for randomly oriented spheroids to retrieve particle size and microphysical parameters.
Abstract: Abstract The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36 h from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, capturing the signature of a severe Saharan dust outbreak episode. The data clearly reveal the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5 km above ground level (a.g.l.) and an upper layer extending between 3.0 and 6.0 km a.g.l. The time evolution of the dust cloud is illustrated and discussed in the paper in terms of several optical parameters (particle backscatter ratio at 532 and 1064 nm, the colour ratio and the backscatter Angstrom parameter). An inversion algorithm was used to retrieve particle size and microphysical parameters, i.e., mean and effective radius, number, surface area, volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution (PSD), from the multi-wavelength lidar data of particle backscattering, extinction and depolarization. The retrieval scheme employs Tikhonov’s inversion with regularization and makes use of kernel functions for randomly oriented spheroids. Size and microphysical parameters of dust particles are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the presence of a fine mode with radii of 0.1–0.2 μm and a coarse mode with radii of 3–5 μm both in the lower and upper dust layers, and the dominance in the upper dust layer of a coarse mode with radii of 4–5 μm. Effective radius varies with altitude in the range 0.1–1.5 μm, while volume concentration is found to not exceed 92 μm3 cm−3. The real and imaginary part of the complex refractive index vary in the range 1.4–1.6 and 0.004–0.008, respectively.

55 citations

Journal ArticleDOI
Abstract: The phase states of atmospheric aerosol particles affect their physical, chemical, and optical properties. Particles with different phase states exhibit different viscosities and various shapes tha...

12 citations

Journal ArticleDOI
TL;DR: Zhang et al. as discussed by the authors examined seasonal characteristics of the aerosol vertical structure and potential variations of aerosol properties before and during the wintertime heating period at SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946°N, 104.137°E, 1961 m ASL), northwest of China.

10 citations

Journal ArticleDOI
TL;DR: In this article, the authors exploit the polarization property of light to investigate the Angstrom exponent describing the wavelength dependence of optical backscatter between two wavelengths, and apply analytical solutions of the Maxwell's equations (Lorenz-Mie theory, spheroidal model) for particle size and complex refractive index for each assigned shape.
Abstract: In this Letter, we exploit the polarization property of light to investigate the Angstrom exponent describing the wavelength dependence of optical backscatter between two wavelengths. Where previous interpretation of Angstrom exponent was that of a particle size indicator, the use of light polarization makes it possible to investigate the Angstrom exponent dependence on the particle shape by separately retrieving the backscattering Angstrom exponent of the spherical (s) and non-spherical (ns) particles contained in an atmospheric particle mixture $(p) = \{s, {\rm ns}\}$(p)={s,ns}. As an output, analytical solutions of the Maxwell’s equations (Lorenz–Mie theory, spheroidal model) can then be applied to investigate the Angstrom exponent dependence on the particle size and complex refractive index for each assigned shape. Interestingly, lidar-retrieved vertical profiles of backscattering Angstrom exponents specific to $s$s- and ns-particles can be used by the optical community to evaluate a range of involved particle sizes and complex refractive indices for both particle shapes, $s$s and ns, as we remotely demonstrate on a case study dedicated to a dust nucleation event.

8 citations

Journal ArticleDOI
TL;DR: In this paper, a technique for determining aerosol type using simulated values of degree of linear polarization as a function of scattering angle is presented, which is determined from retrieved values of the indices of refraction and size parameters as determined from AERONET data sets.

7 citations

References
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Journal ArticleDOI
TL;DR: The operation and philosophy of the monitoring system, the precision and accuracy of the measuring radiometers, a brief description of the processing system, and access to the database are discussed.

6,535 citations


"3+2 + X : what is the most useful d..." refers methods in this paper

  • ...…by spheroids (Dubovik model, Dubovik et al. 2006) developed for the inversion of sunphotometer measurements within the framework of the Aerosol Robotic Network (AERONET, https://aeronet.gsfc.nasa.gov/, Holben et al. 1998) has been implemented in the lidar data inversion algorithm used here....

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Journal ArticleDOI
TL;DR: In this article, the authors used shape mixtures of randomly oriented spheroids for modeling desert dust aerosol light scattering, and the results indicated that nonspherical particles with aspect ratios similar to 1.5 dominate in desert dust plumes, while in the case of background maritime aerosol spherical particles are dominant.
Abstract: [ 1] The possibility of using shape mixtures of randomly oriented spheroids for modeling desert dust aerosol light scattering is discussed. For reducing calculation time, look-up tables were simulated for quadrature coefficients employed in the numerical integration of spheroid optical properties over size and shape. The calculations were done for 25 bins of the spheroid axis ratio ranging from similar to 0.3 ( flattened spheroids) to similar to 3.0 ( elongated spheroids) and for 41 narrow size bins covering the size parameter range from similar to 0.012 to similar to 625. The look-up tables were arranged into a software package, which allows fast, accurate, and flexible modeling of scattering by randomly oriented spheroids with different size and shape distributions. In order to evaluate spheroid model and explore the possibility of aerosol shape identification, the software tool has been integrated into inversion algorithms for retrieving detailed aerosol properties from laboratory or remote sensing polarimetric measurements of light scattering. The application of this retrieval technique to laboratory measurements by Volten et al. ( 2001) has shown that spheroids can closely reproduce mineral dust light scattering matrices. The spheroid model was utilized for retrievals of aerosol properties from atmospheric radiation measured by AERONET ground-based Sun/sky-radiometers. It is shown that mixtures of spheroids allow rather accurate fitting of measured spectral and angular dependencies of observed intensity and polarization. Moreover, it is shown that for aerosol mixtures with a significant fraction of coarse-mode particles ( radii >= similar to 1 mu m), the nonsphericity of aerosol particles can be detected as part of AERONET retrievals. The retrieval results indicate that nonspherical particles with aspect ratios similar to 1.5 and higher dominate in desert dust plumes, while in the case of background maritime aerosol spherical particles are dominant. Finally, the potential of using AERONET derived spheroid mixtures for modeling the effects of aerosol particle nonsphericity in other remote sensing techniques is discussed. For example, the variability of lidar measurements ( extinction to backscattering ratio and signal depolarization ratio) is illustrated and analyzed. Also, some potentially important differences in the sensitivity of angular light scattering to parameters of nonspherical versus spherical aerosols are revealed and discussed.

1,260 citations

BookDOI
01 Jan 2005
TL;DR: In this article, the DIAL Revisited: BELINDA and White-Light Femtosecond Lidar is revisited: BelinDA and Raman Lidars.
Abstract: to Lidar.- Polarization in Lidar.- Lidar and Multiple Scattering.- Lidar and Atmospheric Aerosol Particles.- High Spectral Resolution Lidar.- Visibility and Cloud Lidar.- Differential-Absorption Lidar for Ozone and Industrial Emissions.- Differential-Absorption Lidar for Water Vapor and Temperature Profiling.- Raman Lidar.- Temperature Measurements with Lidar.- Resonance Scattering Lidar.- Doppler Wind Lidar.- Airborne and Spaceborne Lidar.- DIAL Revisited: BELINDA and White-Light Femtosecond Lidar.

681 citations


"3+2 + X : what is the most useful d..." refers background or methods in this paper

  • ...…of aerosol backscatter and extinction coefficients (i.e. the availability of a 3β+2α input data set, also referred to as 3+2 data set) and the mathematically correct description of light scattering by small particles to solve the ill-posed inverse problem at hand (Ansmann and Müller, 2005)....

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  • ...3.3 Inversion of lidar data10 The inversion of multiwavelength lidar data is based on using light-scattering kernels that were computed on the basis of Mie theory (Ansmann and Müller, 2005)....

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  • ...…of multiwavelength aerosol lidar measurements for the retrieval of aerosol microphys-5 ical properties (Müller et al., 1998, 1999a, b, 2001; Veselovskii et al., 2002; Ansmann and Müller, 2005) matured to a stage that allows for automated and unattended data processing (Müller et al., 2014)....

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Journal ArticleDOI
01 Feb 2009-Tellus B
TL;DR: In this paper, the vertical profiles of the linear particle depolarization ratio of pure dust clouds were measured during the Saharan Mineral Dust Experiment (SAMUM) at Ouarzazate, Morocco, close to source regions in May-June 2006, with four lidar systems at four wavelengths (355, 532, 710 and 1064 nm).
Abstract: Vertical profiles of the linear particle depolarization ratio of pure dust clouds were measured during the Saharan Mineral Dust Experiment (SAMUM) at Ouarzazate, Morocco (30.9 ◦ N, –6.9 ◦ E), close to source regions in May–June 2006, with four lidar systems at four wavelengths (355, 532, 710 and 1064 nm). The intercomparison of the lidar systems is accompanied by a discussion of the different calibration methods, including a new, advanced method, and a detailed error analysis. Over the whole SAMUM periode pure dust layers show a mean linear particle depolarization ratio at 532 nm of 0.31, in the range between 0.27 and 0.35, with a mean Angstr¨ om exponent (AE, 440–870 nm) of 0.18 (range 0.04–0.34) and still high mean linear particle depolarization ratio between 0.21 and 0.25 during periods with aerosol optical thickness less than 0.1, with a mean AE of 0.76 (range 0.65–1.00), which represents a negative correlation of the linear particle depolarization ratio with the AE. A slight decrease of the linear particle depolarization ratio with wavelength was found between 532 and 1064 nm from 0.31 ± 0.03 to 0.27 ± 0.04.

482 citations


"3+2 + X : what is the most useful d..." refers background or methods or result in this paper

  • ...While higher dust fractions would be desirable to properly represent pure-dust conditions (see, e.g. Freudenthaler et al. 2009), the general scarcity of suitable measurement data means that this is the "purest" 3+2+3 dust case available to us at the time of this study....

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  • ...Reliable measurements of δ require careful instrument characterisation together with dedicated calibration efforts (Freudenthaler et al., 2009; Freudenthaler, 2016).10 Light scattering by non-spherical particles such as mineral dust poses a great challenge for applications in atmospheric science as…...

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  • ...Values of δ532 were similar to values observed close to dust source regions (Freudenthaler et al., 2009)....

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  • ...Both spectral behaviours are not found in lidar measurements of mineral dust (Freudenthaler et al., 2009; Shin et al.,20 2018)....

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  • ...…particles do not depolarize the emitted laser light, and thus, show values of δ close to zero. depolarisation-ratio measurements with advanced lidars (Freudenthaler et al., 2009) allow for the retrieval15 of the contribution of non-spherical particles to the measured intensive optical parameters…...

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Journal ArticleDOI
TL;DR: The design of the airborne HSRL, the internal calibration and accuracy of the instrument, data products produced, and observations and calibration data from the first two field missions are discussed.
Abstract: A compact, highly robust airborne High Spectral Resolution Lidar (HSRL) that provides measurements of aerosol backscatter and extinction coefficients and aerosol depolarization at two wavelengths has been developed, tested, and deployed on nine field experiments (over 650 flight hours). A unique and advantageous design element of the HSRL system is the ability to radiometrically calibrate the instrument internally, eliminating any reliance on vicarious calibration from atmospheric targets for which aerosol loading must be estimated. This paper discusses the design of the airborne HSRL, the internal calibration and accuracy of the instrument, data products produced, and observations and calibration data from the first two field missions: the Joint Intercontinental Chemical Transport Experiment--Phase B (INTEX-B)/Megacity Aerosol Experiment--Mexico City (MAX-Mex)/Megacities Impacts on Regional and Global Environment (MILAGRO) field mission (hereafter MILAGRO) and the Gulf of Mexico Atmospheric Composition and Climate Study/Texas Air Quality Study II (hereafter GoMACCS/TexAQS II).

426 citations


"3+2 + X : what is the most useful d..." refers background in this paper

  • ...It builds on the heritage of the HSRL-1 system (Hair et al., 2008) but operates at the laser wavelengths of 355, 532, and 1064 nm....

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Trending Questions (1)
What is the input?

The input for the inversion of lidar measurements of non-spherical particles using the spheroid model of Dubovik et al. (2006) includes three backscatter coefficients (β) at 355, 532, and 1064 nm, two extinction coefficients (α) at 355 and 532 nm, and the particle linear depolarization ratio (δ) at one or more of these wavelengths.