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Center Innovation Fund: ARC CIF

Surface Spectroscopy Center of Excellence

Completed Technology Project

Project Description

Surface Spectroscopy Center of Excellence

We propose to develop a national center of excellence in Regolith Radiative Transfer (RRT), i.e., in modeling spectral reflectivity and emissivity of grainy or structured surfaces. The focus is the regime where the structural elements of grainy surfaces have grain sizes and separations of tens of microns, comparable to the wavelengths carrying diagnostic compositional information. This regime is of fundamental interest to remote sensing of planetary and terrestrial surfaces. The core capability on which we will build is an innovative numerical model of a surface composed of grains of arbitrary size, shape, composition, and porosity (Vahidinia et al 2010, 2011, 2012). Our code is an extension of the well-known "Discrete Dipole Approximation" (DDA; Draine and Flatau 1994), expanded to determine the near-field emergent intensity from a "surface" using periodic horizontal boundary conditions. Over the past four years, we have parallelized the code with MPI and OpenMP for efficient operation on the NAS HEC machines. Currently we have shown how increasing particle filling factor alone can affect the scattering properties of ensembles of otherwise identical particles. This effect sets in at surprisingly low filling factors (a few percent or less). The code can handle embedded nanoparticles by using suitable models of how their size changes their refractive indices (for instance, the Drude model for metals). It also can handle compositionally heterogeneous surfaces. In fact, it can handle any surface structure in complete generality. The code is currently limited primarily by memory per processor on the NAS machines, which will grow with time, but we have successfully modeled many cases each containing millions of dipoles to date.

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This is a historic project that was completed before the creation of TechPort on October 1, 2012. Available data has been included. This record may contain less data than currently active projects.