Hannu Parviainen

Rough-surface shadowing of self-affine random rough surfaces

Light scattering from self-affine homogeneous isotropic random rough surfaces is studied using the ray-optics approximation. Numerical methods are developed to accelerate the first-order scattering simulations from surfaces represented as single-connected single-valued random fields, and to store the results of the simulations into a numerical reflectance model. Horizon mapping and marching methods are developed to accelerate the simulation. Emphasis is given to the geometric shadowing and masking effects as a function of surface roughness, especially, to the azimuthal rough-surface shadowing effect.

Scattering from rough thin films: discrete-dipole-approximation simulations.

We investigate the wave-optical light scattering properties of deformed thin circular films of constant thickness using the discrete-dipole approximation. Effects on the intensity distribution of the scattered light due to different statistical roughness models, model dependent roughness parameters, and uncorrelated, random, small-scale porosity of the inhomogeneous medium are studied. The suitability of the discrete-dipole approximation for rough-surface scattering problems is evaluated by considering thin films as computationally feasible rough-surface analogs. The effects due to small-scale inhomogeneity of the scattering medium are compared with the analytic approximation by Maxwell Garnett, and the results are found to agree with the approximation.We investigate the wave-optical light scattering properties of deformed thin circular films of constant thickness using the discrete-dipole approximation. Effects on the intensity distribution of the scattered light due to different statistical roughness models, model dependant roughness parameters, and uncorrelated random small-scale porosity of the inhomogeneous medium are studied. The usability of discrete-dipole approximation to rough-surface scattering problems is evaluated by considering thin films as computationally feasible rough-surface analogs. The effects due to small-scale inhomogeneity of the scattering medium are compared with the analytic approximation by Maxwell Garnett and the results are found to agree with the approximation.

Spins, shapes, and orbits for near-Earth objects by Nordic NEON

The Nordic Near-Earth-Object Network (NEON) observing program accrues knowledge about the physical and dynamical properties of near-Earth objects (NEOs) using state-ofthe-art inverse methods. Photometric and astrometric observations are being carried out at the Nordic Optical Telescope. Here, the NEON observations from June 2004 - September 2006 are reviewed. Statistical orbital inversion is illustrated by the application of the so-called Volume-of-Variation method to NEON observations. Spins and shapes are characterized using shape models that allow analytical computation of disk-integrated brightnesses in arbitrary illumination and observation geometries for Lommel-Seeliger and Lambert scattering laws. The analytical treatment allows error analyses for the spins and shapes using large numbers of discrete sample solutions to the statistical inverse problem. Currently, statistical spin and shape solutions have been derived for 2002 FF12, 2003 MS2, 2003 RX7, 2004 HW as well as for (1685) Toro and (1981) Midas. For (1862) Apollo, an unambiguous spin and shape solution has been obtained using the convex inversion method.