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Radiative-transfer coherent-backscattering database for modeling photometric and polarimetric phase curves

Presentation #411.04 in the session Asteroids: Main Belt (Poster)

Published onOct 23, 2023
Radiative-transfer coherent-backscattering database for modeling photometric and polarimetric phase curves

Photometric phase curves of airless Solar System objects show a distinct opposition effect, nonlinear brightening towards backscattering in the magnitude range. Polarimetric phase curves exhibit predominating negative degree of linear polarization near backscattering, within phase angles less than about 20 degrees. The phenomena are inadequately explained by radiative transfer (RT) models, whereas incorporating coherent backscattering (CB) allows for their complete modeling. Solving the inverse light scattering problem of finding model parameters for the observed phase curves is, however, a laborious effort.

We generate a comprehensive and extensive RT-CB database of photometric and polarimetric phase curves for realistic model regoliths. The initial database contains phase curves as a function of single-scattering albedo, full 4 x 4 single-scattering phase matrix, and regolith mean free path length. For the phase matrix, we incorporate an empirical model (Muinonen and Penttilä, in preparation) that utilizes parameterized phase matrix elements. The model captures overall angular characteristics of many ensemble-averaged experimental and theoretical phase matrix elements and facilitates a strict enforcement of phase-matrix symmetry relations.

The RT-CB database will expedite the process of interpreting the polarimetric and photometric phase curves of airless Solar System objects (cf. Kolokolova et al., this meeting). First, we illustrate the relevance of the empirical phase matrix for experimentally measured and numerically computed single-scattering phase matrices. Second, we provide a comparison of the database phase curves and observed phase curves. Third, with the database as a starting point, we provide tentative constraints for the physical properties of a number of airless Solar System objects.

As a future development of the database, our plan is to introduce a regolith geometry model with particle size distribution and packing factor as well as regolith surface roughness.

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