This book is aimed at students and researchers who wish to use reflectance and emittance as quantitative tools to measure the properties of surfaces and materials. It is intended primarily for use in the interpretation of remote observations of the surfaces of the Earth and other planets, and it will also be useful to chemists, physicists, geologists, engineers and others who deal with particulate media. Topics include propagation and absorption of light in continuous media, reflection by smooth surfaces, scattering by spheres and irregular particles, reflectances and emissivities of particulate media, reflectance and emittance spectroscopy, and the polarization of light scattered by particulate media. Many examples of applications are given.

An approximate analytic solution to the radiative transfer equation describing the scattering of light from particulate surfaces is derived. Multiple scattering and mutual shadowing are taken into account. Analytic expressions for the following quantities are found: bidirectional reflectance, radiance factor, radiance coefficient, normal, hemispherical, Bond, and physical albedos, integral phase function, phase integral, and limb‐darkening profile. Scattering functions for mixtures can be calculated, as well as corrections for comparing experimental laboratory transmission or reflection spectra with observational planetary spectra. An expression for the scattering efficiency of an irregular particle large compared with the wavelength is derived. For closely spaced, nonopaque particles this efficiency is approximated by (1 + αDe)−l, where α is the true absorption coefficient and De is an effective particle diameter of the order of twice the mean particle size. For monomineralic surfaces it is shown that α = ( 1 − w)/wDe, where w is the single‐scattering albedo and can be determined from reflectance measurements of a powder, so that α may be calculated from reflectance. This theory should be useful for interpretations of reflectance spectroscopy of laboratory surfaces and photometry of solar system objects. From photometric observations of a body the following may be estimated: average single‐scattering albedo, average particle phase function, average macroscopic slope, and porosity.

Abstract. The variety of evidence bearing on the nature of space weathering is reviewed. The effects of space weathering include spectral darkening, reddening and subdued absorption bands, and the distinctive magnetic electron spin resonance caused by single-domain metallic iron particles. Ever since the Apollo missions, two paradigms have dominated the thinking of the planetary science community concerning space weathering: (1) the optical effects are caused by impact-vitrified glass in agglutinates, and (2) the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind. However, studies carried out since the Apollo program showed that both of these paradigms are invalid. A hypothesis first suggested by the author and his colleagues 26 years ago, but not generally accepted at that time, now appears to be essentially correct: Both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor-deposited coatings on soil particle surfaces and inside agglutinates. The vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith. The iron is reduced by a physical process, the selective loss of oxygen that occurs during deposition of the vapor, and does not require heating, melting, or a reducing environment. A mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the Moon, Mercury and an S asteroid.

Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.