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Infrared emissivities of powered silicates are shown by experiment to contain new maximums and minimums that are representative of both composition and particle size. A cloudy atmosphere model for radiative transfer in a condensed powder is developed in which the scatter is considered to be both nonconservative and linearly anisotropic. The scattering parameters are computed as functions of frequency from the Mie diffraction theory. Detailed calculations of the spectral emissivity of quartz are presented. The model is shown to account for many features observed experimentally in the spectrums of quartz powders and sand. Changes in the spectrum with particle size can be understood in terms of changes in the albedo for single scattering and the degree of forward scatter with particle size. The principal Christiansen frequencies of silicate powder films obtained from transmission measurements are shown to be diagnostic of mineralogy and to be frequencies of maximum emissivity for powders. The relationship is discussed in detail for quartz.

A variation of the modified Langley plot algorithm is reported here and applied to the retrieval of atmospheric water column abundance from a filtered sunphotometer. In this new methodology an absorption data base (LOWTRAN 7) is used to compute a water abundance versus transmittance curve of growth, rather than the square‐root dependence previously assumed. Validation of the technique is provided from an uncertainty analysis, and plans to further validate using Fourier transform spectrometers are detailed. The new sunphotometer technique is used to report total column water vapor during the First ISLSCP Field Experiment (FIFE), and comparisons are made with abundances retrieved via FIFE radiosonde observations. The sunphotometer data can best be utilized, however, to in turn validate data from airborne or in‐orbit measurements of water vapor. With these flight sensors, horizontal and topographic variability within the scene can be viewed. An example of the airborne data set is given using an image from the airborne visible infrared imaging spectrometer (AVIRIS), as acquired on August 31, 1990.

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Spectral reflectance measurements in the range 0.4–2.5 μm were made for synthetic powder mixtures of a single suite of plagioclase, pyroxene, and ilmenite, which are the principal mineral phase types making up virtually all lunar surface materials studied to date. Binary and ternary data plots of the parameters albedo, band depth, and red to blue ratios versus mixture composition show how variation in the concentration of each mineral phase in a mixture affects changes in the overall reflectance spectrum of the mixture. Principal mixing effects noted are (1) the disproportionate darkening effect of opaque ilmenites and (2) the persistence, the wavelength stability, and the depth versus concentration proportionality of the 1μm band of pyroxene. These results indicate that by comparing the albedo and band depth of an unknown spectrum with calibration data obtained with laboratory standards one can determine the ratio of crystalline phases in the material producing the spectra such as may be obtained telescopically from small areas on lunar and planetary surfaces.