Interpreting asteroid photometry and polarimetry using a model of shadowing and coherent backscattering

The shadow-hiding models for the opposition effect and negative polarization of atmosphereless solar system bodies do not explain some experimental findings, such as the enhancing opposition effect and negative polarization with decreasing particle size down to wavelength scales. The enhancement for laboratory photometric and polarimetric data on artificial glass samples with different particle size is shown. These results are in agreement with the so-called coherent backscattering or interference mechanism proposed for the interpretation of the opposition effect and negative polarization. Two different approaches for describing the opposition effect and negative polarization produced by the shadow-interference mechanism were developed. One is based on exact electromagnetic solutions for simple scattering systems that include dipole-dipole and dipole-surface coupling; The other is based on a point-scatterer approximation characterized by model photometric and polarimetric phase functions, and the mutual shadowing effect is derived using virtual volumes associated with the point-scatterers. Both approaches yield qualitatively similar results, although neither is entirely satisfactory. We regard them as prototypes for a future unified model of shadowing and coherent backscattering. The sharp opposition effect of 44 Nysa and the asteroid albedo-polarization rule are here explained using the point-scatterer approach

Atmospheric Aerosol Limb Scanning Based on the Lunar Eclipses Photometry

The work is devoted to the analysis of the surface photometric observations of two total lunar eclipses in 2004. The lunar surface relative brightness distribution inside the umbra was used to retrieve the vertical distribution of aerosol extinction of the solar radiation expanding by a tangent path and its dependence on the location at the limb of the Earth. The upper altitude of troposphere aerosol layer was estimated for different latitude zones. The correlation between additional aerosol extinction in the upper troposphere and cyclones was investigated.Comment: 17 pages, 10 figures, submitted to Journal of Quantitative Spectroscopy and Radiative Transfe

Character of the opposition effect and negative polarization

Photometric and polarimetric properties at small phase angles were measured for silicates with controlled surface properties in order to distinguish properties that are associated with surface reflection from those that are associated with multiple scattering from internal grain boundaries. These data provide insight into the causes and conditions of photometric properties observed at small phase angles for dark bodies of the solar system. Obsidian was chosen to represent a silicate dielectric with no internal scattering boundaries. Because obsidian is free of internal scatterers, light reflected from both the rough and smooth obsidian samples is almost entirely single and multiple Fresnel reflections form surface facets with no body component. Surface structure alone cannot produce an opposition effect. Comparison of the obsidian and basalt results indicates that for an opposition effect to occur, surface texture must be both rough and contain internal scattering interfaces. Although the negative polarization observed for the obsidian samples indicates single and multiple reflections are part of negative polarization, the longer inversion angle of the multigrain inversion samples implies that internal reflections must also contribute a significant negative polarization component

Lunar dust characterization by polarimetric signature. I. Negative polarization branch of sphere aggregates of various porosities

Context. In support of NASA's exploration program and the return to the Moon, the polarimetric signature of dispersed individual Lunar regolith dust grains is studied to enable the characterization of the dust exopsheric environment by remote, in-situ, and standoff sensing. Aims. We explore the value of the negative polarization branch (NPB) as a signature for characterizing individual grains to determine if it can be used in the same way as for surfaces of planets and atmosphereless bodies. Results. Calculations show that polarization phase curves for spherical grains exhibit a sharp transition over a narrow range of size parameter between two distinct regimes, one typical of Rayleigh scattering and another dominated by a large NPB. The linear polarimetric signature observed for aggregates is a composite of a) the polarization induced by individual grains composing the aggregate and b) the polarization due to the aggregate as a whole dust grain. The weight of each component varies depending on the porosity of the aggregate. An NPB similar to the one observed for atmosphereless astronomical bodies is present for different ranges of the size parameter depending on the value of the porosity. It appears as a remnant of the negative branch exhibited by the single spherical grains. The sharper, narrow negative branch that is measured for some granular surfaces in the laboratory or seen in astronomical observations is not observed here.Comment: 7 pages, 8 figures, accepted for publication in Astronomy & Astrophysic

Note: Utilizing Pb(Zr 0.95Ti 0.05)O₃ Ferroelectric Ceramics to Scale Down Autonomous Explosive-Driven Shock-Wave Ferroelectric Generators

Further miniaturization of recently designed autonomous ferroelectric generators (FEGs) S. I. Shkuratov, J. Baird, and E. F. Talantsev, Rev. Sci. Instrum. 82, 086107 (2011), which are based on the effect of explosive-shock-wave depolarization of poled ferroelectrics is achieved. The key miniaturization factor was the utilization of high-energy density Pb(Zr0.95Ti0.05)O3 (PZT 955) ferroelectric ceramics as energy-carrying elements of FEGs instead of the previously used Pb(Zr0.52Ti0.48)O3 (PZT 5248). A series of experiments demonstrated that FEGs based on smaller PZT 955 ferroelectric elements are capable of producing the same output voltage as those based on PZT 5248 elements twice as large. It follows from the experimental results that the FEG output voltage is directly proportional to the thickness of PZT 955 samples. A comparison of the operation of FEGs based on PZT 955 and on PZT 5248 ferroelectrics is presented

Effect of Shock Front Geometry on Shock Depolarization of Pb(Zr 0.52Ti 0.48)O₃ Ferroelectric Ceramics

By use of experimentation, we detected a shock wave geometry effect on the depolarization of poled PbZr0.52Ti0.48)O3 Z(PZT 52/48) ferroelectrics. It follows from the experimental results that shock front geometry is one of key parameters in the shock depolarization of PZT 5248 ferroelectrics. This shock depolarization effect forms a fundamental limit to miniaturization of explosive-driven shock-wave ferroelectric generators (FEGs). Based on obtained experimental results, we developed miniature generators that reliably produce pulsed voltages exceeding 140 kV