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Light Scattering by Feldspar Particles: Modeling Laboratory Measurements 1 Department of Physics, University of Helsinki, Finland 2 Institute of Astronomy, Kharkov National University, Ukraine 3 Finnish Geodetic Institute, Finland 4 Instituto de Astrofísica de Andalucía, CSIC, Spain 5 Science Systems and Applications, Inc., USA 6 US Army Research Laboratory, USA 7 Space Science Institute, USA Evgenij Zubko 1,2, Karri Muinonen 1,3, Olga Muñoz 4, Timo Nousiainen 1, Yuriy Shkuratov 2, Wenbo Sun 5, and Gorden Videen 6,7

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Laboratory measurements of single-scattering feldspar particles appear to be a huge challenge for modeling Data adapted from Volten et al. 2001: JGR 106, pp –17401

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Data adapted from Dubovik et al. 2006: JGR 111, D11208 Results of fitting feldspar at m

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Data adapted from Dubovik et al. 2006: JGR 111, D11208 Results of fitting feldspar at m

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from Dubovik et al. 2006: JGR 111, D11208 Unfortunately, the parameters were different for the different fits, and Simultaneous inversions of scattering matrices measured at two wavelengths (0.442 m and m) were not successful in that a reasonably good fit was not achieved. The root-mean-square (over all elements) fit for a single wavelength was about 7–10%, while for two wavelengths the root-mean-square fit did not drop below 20%. Little difficulties in modeling

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from Dubovik et al. 2006: JGR 111, D11208 Besides, the best fits are obtained with a mixture of highly oblate and prolate spheroids. However, the feldspar particles look highly irregular with aspect ratio being somewhat about 1. Little difficulties in modeling

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Method: Discrete Dipole Approximation (DDA) Concept: Modeling target with set of small sub-volumes Advantage: Arbitrary shape and internal structure Modeling feldspar with agglomerated debris particles

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More details in, e.g., Zubko et al. 2009: JQSRT 110, pp. 1741–1749 Modeling feldspar with agglomerated debris particles

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Features of agglomerated debris particles: (1) Highly irregular (2) Equi-dimensional (3) Fluffy (packing density =0.236) Modeling feldspar with agglomerated debris particles

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Laboratory measurements of single-scattering feldspar particles Refractive index m is estimated to be in range m = 1.5– – i Data adapted from Volten et al., 2001 SEM image of feldspar Size distribution is retrieved with the laser diffraction method

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SEM image of feldspar Modeling laboratory measurements of feldspar Refractive index: m = i We consider the range of particle radii r from 0.21 m through 2.25 m at =0.442 m: x =3–32 at =0.633 m: x =2.1–22.3 Size distribution: r –2.9 For each size parameter x, we consider a minimum of 500 samples of agglomerated debris particles in random orientations. This makes our analysis being statistically reliable! Size parameter: x = 2 r/

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Modeling laboratory measurements of feldspar at =0.442 m

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Modeling laboratory measurements of feldspar at =0.633 m

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We model light-scattering response measured in feldspar particles at two wavelengths and m. We utilize model of agglomerated debris particles and compute light scattering with the discrete dipole approximation (DDA). Measurements can be satisfactorily reproduced under realistic assumptions on size distribution and refractive index of feldspar particles. Unlike spheroidal model, agglomerated debris particles can fit measurements at both wavelengths. Summary

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