Scattering of light synoptically modeled for particulate planetary surfaces

Scattering and absorption of light in macroscopic discrete random media of densely packed particles (e.g., planetary regoliths) constitutes a computational challenge in electromagnetics described by the Maxwell equations. As a cure, a computational pipeline is here outlined, consisting of a number of separate computational steps. As a starting point, it is practical to make use of ensemble-averaged scattering and absorption characteristics, including experimentally measured or numerically computed scattering matrices. This is enabled by the recently extended radiative-transfer and coherent-backscattering methods
[RT-CB; 1, 2] and by presenting the scattering matrices in a parameterized empirical form (Muinonen & Leppälä, in preparation).

In more detail, first, empirical scattering matrix models are systematically derived for the measured scattering matrices in the Granada-Amsterdam Light Scattering Database [3]. Second, concerning particles in the wavelength scale or smaller, the empirical matrices are transformed into first-order incoherent volume-element matrices. This is accomplished with the help of the Mie scattering and absorption characteristics for the particle size distributions of the database samples. Third, utilization of asymptotically exact computations (like those with the Discrete-Dipole Approximation codes) for particulate media and volume elements described by using the Voronoi tessellation allows for more fundamental theoretical studies. Fourth, scattering and absorption by particles large compared to the wavelength can be incorporated by using their characteristics computed in the geometric optics approximation. Finally, fifth, the volume porosity and surface roughness of the particulate medium can be accounted for by tracing rays in explicit geometric models for the particulate media.

Example modeling is highlighted for the single and multiple scattering of feldspar samples by using the Granada-Amsterdam [4] and Kharkiv measurements [5], respectively. Finally, lunar photometry and polarimetry is addressed by using the pipeline described above [see also, 6].

[1] K. Muinonen, A. Penttilä, JQSRT 324, 109058, 8 pp. (2024).
[2] K. Muinonen, A. Leppälä, J. Markkanen, JQSRT 330, 109226, 12 pp. (2025).
[3] O. Munoz, F. Moreno, D. Guirado, D. D. Dabrowska, H. Volten, J. W. Hovenier, JQSRT 113, 565-574 (2012).
[4] H. Volten, O. Munoz, E. Rol, J. F. de Haan, W. Vassem, J. W. Hovenier, K. Muinonen, T. Nousiainen, JGR 106, D15, 17375-17401 (2001).
[5] Y. Shkuratov, S. Bondarenko, A. Ovcharenko, C. Pieters, T. Hiroi, H. Volten, O. Munoz, G. Videen, JQSRT 100, 340-358 (2006).
[6] Y. Shkuratov, G. Videen, V. Kaydash, Optics of the Moon (Elsevier, 2025).