Spin‐allowed Fe2+ absorption bands occur in the visible and near‐infrared diffuse reflectance spectra of most pyroxenes. The wavelengths of the bands centered near 1 μm and 2 μm vary as functions of pyroxene composition, making possible mineralogical and chemical deductions based on spectral reflectance curves. Typically, pyroxene bands are well developed in relation to absorption features in the spectra of other rock‐forming minerals and glass; thus pyroxene often dominates the spectral curves of pyroxene‐bearing rocks. Telescopic spectra of the moon and some other solar system objects contain absorption features that can be interpreted in terms of pyroxenes mixed with other minerals and/or glass.

A Viking Lander 1 image was modeled as mixtures of reflectance spectra of palagonite dust, gray andesitelike rock, and a coarse rocklike soil. The rocks are covered to varying degrees by dust but otherwise appear unweathered. Rocklike soil occurs as lag deposits in deflation zones around stones and on top of a drift and as a layer in a trench dug by the lander. This soil probably is derived from the rocks by wind abrasion and/or spallation. Dust is the major component of the soil and covers most of the surface. The dust is unrelated spectrally to the rock but is equivalent to the global-scale dust observed telescopically. A new method was developed to model a multispectral image as mixtures of end-member spectra and to compare image spectra directly with laboratory reference spectra. The method for the first time uses shade and secondary illumination effects as spectral end-members; thus the effects of topography and illumination on all scales can be isolated or removed. The image was calibrated absolutely from the laboratory spectra, in close agreement with direct calibrations. The method has broad applications to interpreting multispectral images, including satellite images. , 1981]. This function, which is wavelength 2 dependent, is affected by microscopic shadowing, scattering phase function, and single scattering albedo of particles composing the surface. We assume by the method of separation of variables that p• can be separated into the product of wavelength dependent •x and independent components fl, t(i, e, a)= flU, e, a)•,t(i, e, a) (1) The photometric function p• describes the reflectance of a surface as a function of incidence angle i, emission angle e, and solar phase angle a [e.g., Hapke, 1981; Gradie and Veverka A basic hypothesis underlying our analysis is that the primary component of spectral variation observed in the VikingLander 1 image is the result of linear mixtures of surface 8O98 ADAMS ET AL.: SPECTRAL MIXTURE MODELINGsVIKING LANDER ROCK AND SOIL 8099 materials and shade. Our use of the term shade includes both

The spectral reflectivity (0.30 to 1.10 microns) of several asteroids has been measured for the first time. The reflection spectrum for Vesta contains a strong absorption band centered near 0.9 micron and a weaker absorption feature between 0.5 and 0.6 micron. The reflectivity decreases strongly in the ultraviolet. The reflection spectrum for the asteroid Pallas and probably for Ceres does not contain the 0.9-micron band. Vesta shows the strongest and best-defined absorption bands yet seen in the reflection spectrum for the solid surface of an object in the solar system. The strong 0.9-micron band arises from electronic absorptions in ferrous iron on the M2 site of a magnesian pyroxene. Comparison with laboratory measurements on meteorites and Apollo 11 samples indicates that the surface of Vesta has a composition very similar to that of certain basaltic achondrites.

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