Radiative Transfer of Solar Light in Dense Complex Media : Theoretical and Experimental Achievements by the Planetary Community

Details Radiative Transfer of Solar Light in Dense Complex Media : Theoretical and Experimental Achievements by the Planetary Community Radiative Transfer of Solar Light in Dense Complex Media : Theoretical and Experimental Achievements by the Planetary Community

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.u11a..01d&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #U11A-01

Biology

Quantitative Biology

Quantitative Methods

0659 Random Media And Rough Surfaces, 5464 Remote Sensing, 5470 Surface Materials And Properties, 5494 Instruments And Techniques

Scientific paper

Visible and near infrared imaging spectroscopy is one of the key techniques to detect, map and characterize mineral and volatile species existing at the surface of the planets. Indeed the chemical composition, granularity, texture, physical state, etc, of the materials determine the existence and morphology of the absorption bands. However the development of quantitative methods to analyze reflectance spectra requires mastering of a very challenging physics: the reflection of solar light by densely packed, absorbent and highly scattering materials that usually present a fantastic structural complexity at different spatial scales. Volume scattering of photons depends on many parameters like the intrinsic optical properties, the shapes, sizes and the packing density of the mineral or icy grains forming the natural media. Their discontinuous and stochastic nature plays a great role especially for reflection and shading by the top few grains of the surface. Over several decades, the planetary community has developed increasingly sophisticated tools to handle this problem of radiative transfer in dense complex media in order to fulfill its needs. Analytical functions with a small number of non physical adjusting parameters were first proposed to reproduce the photometry of the planets and satellites. Then reflectance models were built by implementing methods of radiative transfer in continuously absorbent and scattering medium. A number of very restricting hypothesis forms the basis of these methods, e.g. low particles density, scattering treated in the far field approximation. A majority of these assumptions does not stand when treating planetary regoliths or volatile deposits. In addition, the classical methods completely bypass effects due to the constructive interference of scattered waves for backscattering or specular geometries (e.g. the opposition effect). Different, sometimes competing, approaches have been proposed to overcome some of these limitations. In particular Monte Carlo ray tracing simulations have been recently carried out to investigate properties of particulate media that are traditionally ignored or crudely treated: packing density, micro-roughness, etc. The efforts of the community to address the later problems are not only theoretical but also experimental with the development of several dedicated goniometers.

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