Biomedical subjects

J I Peltoniemi

Publications and source records attributed to J I Peltoniemi.

3 recordsLinked to original sources

PubMed1991

Interpretation of the surface brightness of Phobos.

Analysis of disk resolved images of Phobos obtained by the Phobos 2 spacecraft allows us to study the surface scattering law and albedo variations. From low phase angle images we find variations in local geometric albedo approximately 10%, with a correlation length approximately 1km. The scattering law is reasonably well matched by the recent proposed LPI (Lumme et al. 1990a) model, which allows us to deduce a small scale (approximately 1 mm) surface roughness (approximately 0.5), defined here as the rms. tangent of the local surface normal relative to the mean surface normal in the Duxbury (1991) model of Phobos. This value is very close to what has been found for Mercury and the Moon.

Astronomy↗

PubMed1990

Diffuse reflection from a stochastically bounded, semi-infinite medium.

In order to determine the diffuse reflection from a medium bounded by a rough surface, we consider the problem of radiative transfer in a boundary layer characterized by a statistical distribution of heights. For the case that the surface is defined by a multivariate normal probability density, we derive the propagation probability for rays traversing the boundary layer and, from that probability, a corresponding radiative transfer equation. A solution of the Eddington (two stream) type is found explicitly, and examples are given. The results should be applicable to reflection from the regoliths of solar system bodies, as well as from a rough ocean surface.

Astronomical Phenomena↗

PubMed1989

Scattering of light by stochastically rough particles.

The single particle phase function and the linear polarization for large stochastically deformed spheres have been calculated by Monte Carlo simulation using the geometrical optics approximation. The radius vector of a particle is assumed to obey a bivariate lognormal distribution with three free parameters: mean radius, its standard deviation and the coherence length of the autocorrelation function. All reflections/refractions which include sufficient energy have been included. Real and imaginary parts of the refractive index can be varied without any restrictions. Results and comparisons with some earlier less general theories are presented. Applications of this theory to the photometric properties of atmosphereless bodies and interplanetary dust are discussed.

Astronomical Phenomena↗