Active remote sensing of atmospheric dust using relationships between their depolarization ratios and reflectivity.

The backscattered light from agglomerated debris particles shows that an approximate linear correlation exists between the logarithm of the geometric albedo $ \log(A )$ of polydispersions of agglomerated debris particles and their lidar linear or circular depolarization ratios, $ \unicode{x00B5}_L$ and $ \unicode{x00B5}_C$. The nature of the relationship depends on the complex refractive index of the particles in the distribution. This extension of the Umov law can be used for lidar and radar characterizations by placing constraints on the reflectivity of the particles.

Interpolating light-scattering properties of irregularly shaped, absorbing particles.

Success in developing remote-sensing methods is largely based on adequate modeling of target-particle shapes. In various terrestrial and cosmic applications, submicrometer- and micrometer-sized dust particles appear to have a highly irregular morphology. Light scattering by such irregularly shaped particles can be computed only with a numerical technique that, in practice, is a time-consuming approach, demanding significant computational resources.

Umov effect in single-scattering dust particles: effect of irregular shape.

The Umov effect manifests itself as an inverse correlation between the light-scattering maximum of positive polarization P and the geometric albedo A of the target. In logarithmic scales, P is linearly dependent on A. This effect has been long known in the optics of particulate surfaces and, recently, it was extended for the case of single-scattering dust particles whose size is comparable to the wavelength of the incident light.

Phase-ratio imaging as applied to desert sands for tracking human presence.

The phase function is a measure of the light-scattered intensity, or radiance, as a function of scattering angle θ. A phase ratio is the ratio of two values of the phase function measured at different scattering angles and relates to the slope of the phase function. By taking the ratio of two images acquired at different illumination or observation conditions, a phase-ratio image can be constructed.

Modeling light scattering by forsterite particles.

Laboratory optical measurements of forsterite particles reveal remarkably similar light-scattering responses in two samples that were thought to obey different size distributions. These measurements are modeled with irregularly shaped agglomerated debris particles having a refractive index of m=1.6+0.

Light scattering by random irregular particles of two classes of shape.

We calculate light scattering properties of random irregular particles of two different classes of shape, compact Gaussian random field particles and agglomerated debris particles, at size parameters X=50 and X=32. Surprisingly, very similar angular dependencies of all nonzero scattering matrix elements are obtained for both classes in the case of nonabsorbing material. For highly absorbing particles external scattering becomes dominant, which introduces a difference in the positive polarization due to different morphologies of their surfaces.

Effect of the orientation of the optic axis on simulated scattering matrix elements of small birefringent particles.

We study how the orientation of the optic axis affects single-scattering properties for small, birefringent calcite particles simulated using DDSCAT 7.1.1.

Interpretation of single-particle negative polarization at intermediate scattering angles.

We study the interrelation of the internal field of irregular particles to the far-field scattering characteristics by modifying the internal field of dipole groups. In this paper, we concentrate on the longitudinal component, i.e.

Validity criteria of the discrete dipole approximation.

There are two widely accepted restrictions on the application of the discrete dipole approximation (DDA) in the study of light scattering by particles comparable to the wavelength: (1) when considering dielectric particles, the size of the cells must satisfy the condition kd|m|<0.5, where k is the wavenumber, d is the size of the cells, and m is the complex refractive index of the constituent material and (2) when considering conductive particles, the size of the cells must be small enough to reproduce sufficiently the evolution of the electromagnetic field in the skin layer. We examine both restrictions when the DDA is applied to irregularly shaped particles and show that its restrictions are not as strong as is widely accepted.

Discrete dipole approximation simulations of scattering by particles with hierarchical structure.

We use the discrete dipole approximation (DDA) method to calculate the intensity and the linear polarization degree of light scattered by agglomerated debris particles with hierarchical structure as functions of size parameter (varying from x = 2 to x = 14) and phase angle. Such structures are important, e.g.

Backscattering and negative polarization of agglomerate particles.

We used the discrete dipole approximation to study the backscattering of agglomerate particles consisting of oblong monomers. We varied the aspect ratio of the monomers from approximately 1 (sphere) to 4, while we kept the total particle volume equivalent to that of an x = 10 sphere for m = 1.59 + i0 and 1.