177,245 research outputs found
Radar Signal Propagation and Detection Through Ice
No full textIn this paper we describe the existing and planned radar measurements of the
planetary bodies. The dielectric properties of water ice and other potential surface and subsurface
materials are discussed, as well as their dependency on temperature and structure.
We then evaluate the performance of subsurface sounding radars using these parameters.
Finally we describe some laboratory technique to help interpret the radar data, presenting
some results obtained using dielectric spectroscopy methods
INNOVATIVE FRACTAL-BASED MODELS FOR RADAR ALTIMETER DATA
No full textAn innovative electromagnetic model for the radar echoes received by a
microwave altimeter is proposed: it is based on fractal models employed both to describe the natural surface and to evaluate the surface scattering behaviour. The scattering surface is modelled by means of the fractional Brownian model (fBm) process, whose realizations are obtained by using the band-limited Weierstrass-Mandelbrot (WM) function. The scattering
process is evaluated by means of the Physical Optics solution specifically derived for fractal surfaces. Rationale to apply this solution to the evaluation (in time domain) of the received echoes is provided. Dependence of the return pulse shapes on surface topography at different roughness scales is highlighted: some relevant meaningful examples are presented. Simulation
results are provided to show the potential of the proposed technique that could be the fundamental element to generate an atlas of expected returns from a given radar altimeter
A simple inversion model for the estimation of subsurface features of Mars poles
No full textRadar observations from Marsis have demonstrated that Martian Polar Layered Deposits (PLD's) are very transparent to radar waves. Thus, the sounder is able to detect the presence of subsurface reflections in the polar regions below the ice-rich layered deposits. The analysis of radar data makes it possible to gain information about some physical features of Mars surface. In this work an electromagnetic inversion model is used to characterize the shallower structures. This approach assumes that structure consists of layers with parallel plane interfaces and that the electromagnetic properties of the first layer are known a priori. Under these assumptions it is possible to estimate the dielectric permittivity of the subsurface structure. The inversion method has been tested in an area of South Pole and reconstruction results are shown
Surface and subsurface radar backscattering coefficient over the Martian South Polar Layered Deposits from MARSIS data
No full textNote Illustrative della Carta geologica d'Italia alla scala 1:50.000, F. 501 Orosei, Servizio Geologico d'Italia - ISPRA
No full text<p>Note illustrative redatte per il Foglio geologico n. 501 Orosei della Carta Geologica d'Italia alla scala 1:50.000. 230 pp.</p>
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Osservazioni preliminari sui vertebrati fossili plio-pleistocenici del Monte Tuttavista (Orosei, Sardegna)
No full textIn this paper the preliminary results of the study of fossil vertebrates collected in numerous fissure fillings of Monte Tuttavista (Orosei, Eastern Sardinia) are published. Five species of fishes, four species of amphibians, eight species of reptiles, twenty-two species of birds and twenty-seven species of mammals have been identified. All these taxa belong to at least four successive assemblages, spanning from the Late Pliocene to the Holocene
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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