Joop W Hovenier

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We derive theoretically and validate numerically general relationships for the elements of the backscattering matrix and for the linear, delta(L), and circular, delta(C), backscattering depolarization ratios for nonspherical particles in random orientation. For the practically important case of randomly oriented particles with a plane of symmetry or(More)
[1] We present measurements of the phase function and degree of linear polarization for unpolarized incident light as a function of the scattering angle for El Chichón and Pinatubo volcanic ashes at 633 nm. The results are combined and compared with those for Pinatubo at 442 nm and Lokon volcanic ash at 442 and 633 nm [Volten et al., 2001]. The three(More)
We consider two topics pertaining to light scattering by circular cylinders. (A) Scattering properties of cylinders with increasing aspect ratio are studied. It is shown that the solution for finite cylinders does not converge to the solution for infinitely long cylinders if the aspect ratio increases. This is due to differences in the treatment of(More)
We discuss the composition and size distribution of the dust in the coma of comet Hale-Bopp. We do this using a model fit for the infrared emission measured by the infrared space observatory (ISO) and the measured degree of linear polarization of scattered light at various phase angles and wavelengths. The effects of particle shape on the modeled optical(More)
Changes in the radiance and state of polarization of a beam of radiation can often be described by means of a pure Mueller matrix. Such a 4 × 4 matrix transforms Stokes parameters and can be expressed in terms of the elements of a 2 × 2 Jones matrix. Relations between the two types of matrix are discussed. Explicit expressions are given for changes of a(More)
We model the 10 µm absorption spectra of nonspherical particles composed of amorphous silicate. We consider two classes of particles, compact ones and fractal aggregates composed of homogeneous spheres. For the compact particles we consider Gaussian random spheres with various degrees of non-sphericity. For the fractal aggregates we compute the absorption(More)
[1] We present measurements of the whole scattering matrix as a function of the scattering angle at a wavelength of 632.8 nm in the scattering angle range 3°–174° of randomly oriented particles taken from seven samples of volcanic ashes corresponding to four different volcanic eruptions: The samples were collected at different distances from the vent. The(More)
Starting from first principles, we present a detailed analysis of the concept of single scattering of light by a small volume element filled with sparsely and randomly positioned particles. We first derive the formulas of the far-field single-scattering approximation, which treats the volume element as a single scatterer, and discuss its range of(More)
Record-low ozone (O3) column densities (with a minimum of 222 DU) were observed over the Lauder NDSC (Network for the Detection of Stratospheric Change) station (45 • S, 170 • E) in August 1997. Possible causes are examined using height-resolved O3 measurements over Lauder, and high-resolution reverse trajectory maps of O3 (initialised with Microwave Limb(More)
In this paper we study the combined effects of size and shape of small solid state particles on the absorption, emission and scattering characteristics. We use the statistical approach to calculate these optical properties. In this approach the average optical properties of an ensemble of particles in random orientation are represented by the average(More)