Fully polarimetric measurements of robotically fabricated dense media targets

摘要

Many environmental features such as sea ice, snow, and soils can be considered to be dense media. In order to better understand the microwave scattering mechanisms involved in such media, synthetic targets simulating certain electrical behaviors are created. These targets are composed of lead-glass spheres imbedded in polystyrene sheets. The locations of these spheres are predetermined by a Monte Carlo simulation, and their placements are implemented by a robotic arm. By constructing various volume fraction targets in this fashion and performing polarimetric measurements, the authors are able to study scattering effects due to particle position correlation, close spacing between scatterers, volume fraction, and ka. The fabrication technique employed by the Wave Scattering Research Center allows the user to define the radius of the scatterer, radius of the target, volume fraction, height of the target, and the probability distribution parameters for scatterer positions. The authors have recently fabricated and performed measurements over 6-15 GHz on 5, 8, 11, 14, and 20 percent volume fraction targets consisting of 7 mm radius lead-glass sphere scatterers embedded in polystyrene. Data for all four linear polarizations are consistent in that backscattering as a function of volume fraction increases up to about 14%, but shows a drop by 20% volume fraction for ka values near one. The co-polarized data show that the trends of all measurements as a function of frequency (or ka) are consistent with those of the theoretical scattering of a single sphere, although the levels differ from single sphere approximations. This paper compares co- and cross-pol measurements of synthetic dense media with theoretical results obtained using the single scattering approximation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>