Analytic approximation to randomly oriented spheroid extinction

Evans, B. T. N.; Fournier, Georges

doi:10.1364/ao.33.005796

Cited by 17 publications

(4 citation statements)

References 10 publications

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“…For the calculations of attenuation by nonspherical particles we used the approximation of Fournier and Evans. 26,27 Comparing this approximation with results from the more rigorous but size-restricted T-matrix method, 28,29 we found excellent agreement as did Evans and Fournier. 27 We calculate the spectral attenuation for two nonspherical particles oblate spheroids with an axis ratio of 3 and prolate spheroids with an axis ratio of 1͞3.…”

Section: Methodssupporting

confidence: 65%

Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution

Boss¹,

Twardowski²,

Herring³

2001

Appl. Opt.

251

232

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The link between the spectral shape of the beam attenuation spectrum and the shape of the particle size distribution (PSD) of oceanic particles is revisited to evaluate the extent to which one can be predicted from the other. Assuming a hyperbolic (power-law) PSD, N(D) ? D(-xi), past studies have found for an infinite distribution of nonabsorbing spheres with a constant index of refraction that the attenuation spectrum is hyperbolic and that the attenuation spectral slope gamma is related to the PSD slope xi by xi = gamma + 3. Here we add a correction to this model because of the finite size of the biggest particle in the population. This inversion model is given by xi = gamma + 3 - 0.5 exp(-6gamma). In most oceanic observations xi > 3, and the deviation between these two models is negligible. To test the robustness of this inversion, we perturbed its assumptions by allowing for populations of particles that are nonspherical, or absorbing, or with an index of refraction that changes with wavelength. We found the model to provide a good fit for the range of parameters most often encountered in the ocean. In addition, we found that the particulate attenuation spectrum, c(p)(lambda), is well described by a hyperbolic relation to the wavelength c(p) ? lambda(-gamma) throughout the range of the investigated parameters, even when the inversion model does not apply. This implies that knowledge of the particulate attenuation at two visible wavelengths could provide, to a high degree of accuracy, the particulate attenuation at other wavelengths in the visible spectrum.

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Section: Methodssupporting

confidence: 65%

Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution

Boss¹,

Twardowski²,

Herring³

2001

Appl. Opt.

251

232

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“…This result is consistent with previous research. 17 Our new ADT expressions can also be used to evaluate the gradual change from a finite cylinder to an infinite cylinder. This is demonstrated in Fig.…”

Section: A Cases In Which End Effects Can Be Ignoredmentioning

confidence: 99%

“…Similar efforts were made to modify the original ADT extinction for spheroids. 16,17 Empirical functions are also given in Refs. 16 and 17 that bridge the Rayleigh and ADT extinction to improve the ADT performance in the small particle range.…”

Section: Nonsphericity Influence On the Accuracy Of Anomalous Diffracmentioning

confidence: 99%

“…13 ADT has been widely used in studying scattering properties and radiative effects of cirrus clouds on climate. 2,14 New research on ADT is directed toward modifying van de Hulst's original theory to extend the range of its applicability [15][16][17] and toward formulating ADT for nonspherical particles. 14,18 -24 ADT is drawing increased attention as a potentially better approximation for nonspherical ice crystals than commonly used equivalent spheres.…”

Section: Introductionmentioning

confidence: 99%

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Anomalous diffraction theory for arbitrarily oriented finite circular cylinders and comparison with exact T-matrix results

1998

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A general method is developed to formulate extinction and absorption efficiency for nonspherical particles at arbitrary and random orientations by use of anomalous diffraction theory (ADT). An ADT for finite circular cylinders is evaluated as an example. Existing ADT's for infinite cylinders at arbitrary orientations and for finite cylinders at the normal incidence are shown to be special cases of the new formulation. ADT solutions for finite cylinders are shown to approach the rigorous T-matrix results when the refractive indices approach unity. The importance of some physical processes that are neglected in the ADT approximation are evaluated by comparisons between ADT and rigorous calculations for different particle geometries. For spheres, van de Hulst's ADT and Mie theory are used, whereas the ADT that we present and T-matrix calculations are used for cylinders of different diameter-to-length ratios. The results show that the differences in extinction between ADT and exact solutions generally decrease with nonsphericity. A similar decrease occurs for absorption at wavelengths of relatively strong absorption. The influence of complex refractive index is evaluated. Our results suggest that ADT may provide a useful approximation in parameterization and remote sensing of cirrus clouds in the Christiansen bands where the real part of the refractive index approaches unity and/or where relative absorption is strong.

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References

2011

Optical Properties of Nanoparticle Systems

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Analytic approximation to randomly oriented spheroid extinction

Cited by 17 publications

References 10 publications

Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution

Shape of the particulate beam attenuation spectrum and its inversion to obtain the shape of the particulate size distribution

Anomalous diffraction theory for arbitrarily oriented finite circular cylinders and comparison with exact T-matrix results

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