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The Imager for Mars Pathfinder (IMP) returned sequences of images of the Martian sky characterizing the size distribution, optical constants, and nature of the aerosols suspended in the atmosphere of Mars. These sequences were executed when the solar elevation angle was approximately 15° and consisted of images near the elevation of the Sun, spanning a range in azimuth from about 4° to 180° from the Sun. Images were obtained at four wavelengths from 444 to 965 nm. From one sequence of observations, results are shown from a comparison of absolute photometry of the Martian sky with multiple scattering models. Results include the following. (1) The geometric cross-section-weighted mean particle radius is 1.6 ± 0.15 μm almost independent of the assumed width (variance) of the size distribution. (2) The imaginary refractive index shows a steep increase with wavelength from 670 nm to shorter wavelengths, and a shallow increase toward longer wavelengths, consistent with the reflection spectrum observed by IMP for Martian soil. (3) For each assumed variance, two parameters governing the slope and curvature of the portion of the phase function due to internally transmitted light are found uniquely as functions of wavelength. (4) The variance of the gamma size distribution is difficult to constrain from these observations alone. The shape of the single scattering phase functions derived from the IMP observations is compared to laboratory measurements of powder samples. One sample of irregular particles has a single scattering phase function quite similar to that derived for Mars. Overall, the results for the mean cross-section-weighted size and imaginary refractive index as a function of wavelength are in remarkably good agreement with the revised analysis by Pollack et al. [1995] of the observations made by the Viking lander 20 years earlier.

With the goal of improving our understanding of how small mineral dust particles scatter light at visible and near-infrared wafelengths we measured the scattering phase function and linear polarization of small mineral dust particles over the scattering angle range 15 to 170 at three wavelengths (0.47, 0.652,and 0.937 m).

A line at 1280 A, due to Raman scattering of solar Lyman alpha (Ly-alpha) in the atmosphere of Uranus, has been detected by the Voyager Ultraviolet Spectrometer. The measured intensity of 40 + or - 20 R implies that 200 R to 500 R of the measured 1500 R Ly-alpha intensity at the subsolar point is due to Rayleigh scattering of the solar line. The presence of Rayleigh and Raman scattering at 1216 A suggests that the Uranian atmosphere is largely devoid of absorbing hydrocarbons above the 0.5 mbar level. The most natural explanation of this depletion is very weak vertical mixing equivalent to an eddy coefficient on the order of 200 sq cm/sec between 0.5 mbar and 100 mbar.

In the period plus or minus 4 days from Jovian pericenter, Pioneer 10 returned data from 153 imaging sequences. Data were obtained with the imaging photopolarimeter, a 2.54-cm-diam and 8.6-cm-focal-length steerable telescope configured as a narrow beam (0.5-mrad) photometer in a spin scan mode of operation. Images were obtained in two spectral bands (390 to 500 nm and 595 to 720 nm), and seven of the most interesting pictures are shown and discussed.

The solar flux radiometer (LSFR) aboard the Pioneer Venus (PV) sounder probe measured the intensity of sunlight in five directions to the vertical using narrow angular fields of view. The measurements in a narrow spectral channel (0.59–0.67 µm) and two broad channels (0.4–1.0 and 0.4–1.8 µm) were reduced to yield the profiles of upward and downward solar flux with a vertical resolution of 100–500 m. All the flux profiles show three distinct cloud layers with bottoms at altitudes of 57.5, 49.7, and 47.9 km. The azimuthal structure of the intensity samples at the highest altitudes implies a cloud optical depth between 3.5 and 4.0 above 64.3 km. The narrow-band data were interpreted to give the optical depths and single scattering albedos of the clouds at a wavelength of 0.63 µm. The results for the upper cloud are generally consistent with those reported by the cloud particle size spectrometer (LCPS) experiment on PV. In the middle and lower cloud the LSFR data imply that the largest particle size mode has about one third the optical depth deduced from the LCPS data under the assumption that these particles are spherical. The total optical depth of the clouds was found to be about 25. Models of the broad-band fluxes confirm these conclusions and indicate that about half the sunlight absorbed by Venus is absorbed above our first measurements. In addition, absorption of solar radiation occurs in the upper cloud and below 35 km; the middle and lower cloud layers absorb remarkably little sunlight. Models consistent with our measured flux profiles and the spherical albedo of Venus were used to scale our measured net fluxes to a bolometric globally averaged solar energy deposition profile, assuming that the sounder site is typical of planetwide conditions. Averaged over the planet, about 17 W/m² are absorbed at the ground (some 2.5% of the total solar energy incident on the planet). The solar net flux profile in the lower atmosphere is not very sensitive to changes in the thickness of the nearly conservative lower cloud.

In the present paper, the single-scattering phase function of Saturn's aerosols is determined from the vertical structure of Saturn's atmosphere, derived in a previous analysis, and Pioneer's imaging photometry of bright and dark zones on Saturn in red and blue light. The single-scattering phase function is well represented by a combination of two Henyey-Greenstein functions. Moderately forward scattering functions fit well both in red and blue light, although a definite difference between the two colors is found.