Microwave backscattering by nonspherical ice particles at using second-order perturbation series

Nousiainen, Timo; Muinonen, K.; Avelin, Juha; Sihvola, Ari

doi:10.1016/s0022-4073(01)00035-8

Cited by 20 publications

(6 citation statements)

References 27 publications

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“…It is questionable if the T‐matrix method would work well for larger particles: our results indicate that the surface structure is very important for scattering properties of large particles, and the T‐matrix method cannot handle rough surface. Other methods applicable for small particles include the second‐order perturbation series approximation for Gaussian random spheres [ Muinonen , 2000b; Nousiainen et al , 2001], and so‐called volume‐integral methods which can handle complex geometries. For example, a finite difference time domain method (FDTD) can be used up to x = 20 with ensemble averaging (P. Yang, personal communication, 2001).…”

Section: Discussionmentioning

confidence: 99%

Scattering of light by large Saharan dust particles in a modified ray optics approximation

2003

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[1] Single scattering by randomly oriented Saharan sand, silt, and clay particles is studied at 441.6 nm wavelength. Numerical simulations using the ray optics approximation and the Lorenz-Mie theory are compared with laboratory measurements of scattering matrix elements reported in the literature. The ray optics approximation is modified with ad hoc simple schemes of Lambertian surface elements and internal screens to study the effect of small-scale surface roughness and internal structures, respectively. Two different Lambertian reflection/refraction matrices with varying depolarization characteristics are applied. Model particle shapes are based on a tentative shape analysis of real Saharan particles. It is found that the traditional ray optics approximation agrees well with measurements only if unrealistically spiky particle shapes and an imaginary part of the refractive index (Im(m)) that is rather small compared with the typical values given in the literature are used. When the Lambertian schemes are applied, the agreement with measurements clearly improves. More importantly, good agreement can then be achieved using realistic particle shapes; this too requires a rather small Im(m). If Im(m) values corresponding to typical values in the literature are used, good fits can be achieved, but unrealistically spiky particle shapes have to be used. Our findings also indicate that sophisticated single-scattering modeling is important even below the ray optics domain. Finally, we demonstrate the importance of sophisticated single-scattering modeling for radiative flux and radiance calculations.INDEX TERMS: 0669 Electromagnetics: Scattering and diffraction; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: light scattering and absorption, desert dust particles, ray optics, planetary atmospheres, shape modeling of irregular particles, radiative transfer Citation: Nousiainen, T., K. Muinonen, and P. Räisänen, Scattering of light by large Saharan dust particles in a modified ray optics approximation,

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Section: Discussionmentioning

confidence: 99%

Scattering of light by large Saharan dust particles in a modified ray optics approximation

2003

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“…In particular, [81] did not consider Gaussian spheres with different angular correlation, which might impact depolarization considerably. For example, [82] found that, for backscattering and small size parameters, highest depolarizations were obtained with correlation lengths that produced elliptical deformation, that is, non-sphericity in its largest scale.…”

Section: Overall Nonsphericitymentioning

confidence: 99%

Modelling radiometric properties of inhomogeneous mineral dust particles: Applicability and limitations of effective medium theories

Kahnert

2015

Journal of Quantitative Spectroscopy and Radiative Transfer

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This review paper provides an overview over model geometries for computing light scattering by small particles. The emphasis is on atmospheric optics, although much of this review will also be relevant to neighbouring fields, in particular to astronomy. Various morphological particle properties are discussed, such as overall nonsphericity, pristine shapes, aggregation, and different forms of inhomogeneity, e.g. porous and compact inhomogeneous morphologies, as well as encapsulated aggregates. Models employed to reproduce the optical properties of complex particles range from strongly simplified to highly realistic and morphologically sophisticated model geometries. Besides reviewing the most recent literature, we discuss the idea behind models of varying degree of complexity with regard to the intended use of the models. Applications range from fundamental studies of light scattering processes to routine applications of particle optics look-up tables in operational modelling systems.

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“…S 22 /S 11 is sometimes regarded as the indicative element of nonsphericity but it must be noted that the effect is not systematic: here, Sil I shows the strongest depolarization at small size parameters of all the particles, while for larger x it becomes the weakest. Incidentally, Nousiainen et al (2001) noted for microwave backscattering by small graupel particles that the largest-scale deviations from nonsphericity, related to elongation of the particle, were most efficient in depolarizing the backscattered radiation. Our findings here are consistent with this, also suggesting that when the size parameter increases, smaller-scale features in particles become relatively much more important for depolarization, which is quite reasonable.…”

Section: H Lindqvist Et Al: Scattering By Realistic Inhomogeneous mentioning

confidence: 99%

Single scattering by realistic, inhomogeneous mineral dust particles with stereogrammetric shapes

et al. 2014

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Abstract. Light scattering by single, inhomogeneous mineral dust particles was simulated based on shapes and compositions derived directly from measurements of real dust particles instead of using a mathematical shape model. We demonstrate the use of the stereogrammetric shape retrieval method in the context of single-scattering modelling of mineral dust for four different dust types -all of them inhomogeneous -ranging from compact, equidimensional shapes to very elongated and aggregate shapes. The three-dimensional particle shapes were derived from stereo pairs of scanningelectron microscope images, and inhomogeneous composition was determined by mineralogical interpretation of localized elemental information based on energy-dispersive spectroscopy. Scattering computations were performed for particles of equal-volume diameters, from 0.08 µm up to 2.8 µm at 550 nm wavelength, using the discrete-dipole approximation. Particle-to-particle variation in scattering by mineral dust was found to be quite considerable and was not well reproduced by simplified shapes of homogeneous spheres, spheroids, or Gaussian random spheres. Effective-medium approximation results revealed that particle inhomogeneity should be accounted for even for small amounts of absorbing media (here up to 2 % of the volume), especially when considering scattering by inhomogeneous particles at size parameters 3 < x < 8. When integrated over a log-normal size distribution, the linear depolarization ratio and singlescattering albedo were also found to be sensitive to inhomogeneity. The methodology applied is work-intensive and the light-scattering method used quite limited in terms of size parameter coverage. It would therefore be desirable to find a sufficiently accurate but simpler approach with fewer limitations for single-scattering modelling of dust. For validation of such a method, the approach presented here could be used for producing reference data when applied to a suitable set of target particles.

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Microwave backscattering by nonspherical ice particles at using second-order perturbation series

Cited by 20 publications

References 27 publications

Scattering of light by large Saharan dust particles in a modified ray optics approximation

Scattering of light by large Saharan dust particles in a modified ray optics approximation

Modelling radiometric properties of inhomogeneous mineral dust particles: Applicability and limitations of effective medium theories

Single scattering by realistic, inhomogeneous mineral dust particles with stereogrammetric shapes

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