I. Silicon Vidicon Imaging of Jupiter 4100-8300Å: Spectral Reflectivity, Limb-Darkening, and Atmospheric Structure. II. Simultaneous Ultraviolet (0.36 µm) and Infrared (8-20 µm) Imaging of Venus: Properties of Clouds in the Upper Atmosphere

Citation

Diner, David Joseph (1978) I. Silicon Vidicon Imaging of Jupiter 4100-8300Å: Spectral Reflectivity, Limb-Darkening, and Atmospheric Structure. II. Simultaneous Ultraviolet (0.36 µm) and Infrared (8-20 µm) Imaging of Venus: Properties of Clouds in the Upper Atmosphere. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/r1rr-5q90. https://resolver.caltech.edu/CaltechTHESIS:10212024-225714489

Abstract

Part 1 presents the results of high spatial resolution area photometry of Jupiter in six continuum wavelength channels from 4100-8300Å. Spectral reflectivity and limb-darkening data in belts and zones are fitted by a simple semi-infinite homogeneous scattering model which provides a convenient parameterization of the results, as well as a determination of the spectral and spatial variations in the continuum single scattering albedo and information regarding the shape of the single scattering phase functions. It is found that belts are generally more backscattering than zones, particularly in the blue, and there is a trend toward increased forward scattering at longer wavelengths. The numerical results are compared to earlier ground-based observations of jovian limb-darkening (Harris, 1961; Binder and McCarthy, 1973; Pilcher and Kunkle, 1976) and significant disagreement is found in some cases, Extrapolations of the limb­ darkening data to 12° phase angle are compared with the results of the Pioneer 10-imaging photopolarimeter (IPP) experiment (Tomasko et al., 1976). Although there is quantitative disagreement between the vidicon results and the IPP data, the ground-based and Pioneer 10 results show the same relative spectral and regional trends in the shape of the limb structure profiles from the blue to the red and between a belt and a zone. The limb-darkening profiles are also com­ pared to models derived from measurements of the spatial distribution of equivalent width of the H₂ 4-0 S(1) quadrupole line (Cochran, 1976). It is found that these models fare reasonably well in the South Tropical Zone but are much too limb-darkened relative to the data in the North Equatorial Belt. A discussion of the possible causes of the differences between the vidicon data and other ground­ based, Pioneer 10, and spectroscopic results is presented.

Some numerical examples of limb-darkening expected from simple models are presented. In particular, the effects of Rayleigh scat­tering, either by a fine, colored dust, or by the gaseous atmosphere on the spectral characteristics of limb-darkening are investigated. It is found that the observed backscattering may be explained by a combination of molecular scattering and scattering by small dust particles, and the increased forward scattering in the red arises from the λ⁻⁴ dependence of Rayleigh scattering optical depth and inclusion of forward scattering cloud particles. Such a model works reasonably well in the North Equatorial Belt, but predicts a spectral variation in limb-darkening that is greater than the observations imply for the South Tropical Zone.

Part 2 discusses high spatial resolution images of Venus which were obtained in the 0.36 µm and 8-20 µm spectral regions throughout the 1974, 1975, and 1977 apparitions. The observing system, method of image acquisition, and data reduction and processing techniques are presented along with a discussion of the spectral, temporal, and spatial characteristics of the infrared and ultraviolet flux from the planet, The infrared data are compared with previous ground­ based results obtained at lower spatial and spectral resolution (Sinton and Strong, 1960; Murray et al., 1963; Westphal et al., 1965; Ingersoll and Orton, 1974) and Venera 9 and 10 infrared radio­ meter results (Ksanfomality et al., 1976).

Day-night contrasts in equatorial infrared flux were observed in images in which the evening and morning terminators were near the central meridian. A systematic increase in 8-14 µm flux associated with the emergence of the atmosphere from daylight into evening was observed, and is shown to exhibit significant day-to-day variability, The data also show that the daytime side of the morning terminator is warmer than the dark side, but this night-day asymmetry is system­atically smaller than the day-night brightening seen in the Venus evening.

South and north infrared polar anomalies similar to the one observed near the Venus south pole by Murray et al, (1963) have been observed during the 1974 and 1975 apparitions, respectively. The ob­servations indicate that the feature is most prominent between Venus midnight and dawn.

The infrared limb-darkening in the equatorial and polar direc­tions are compared and it is seen that the magnitude and spectral variation of the polar darkening are in general greater than the equatorial darkening. The magnitude of the equatorial darkening is consistent with a temperature lapse rate of roughly -3°K/km, assuming a model in which aerosol is distributed exponentially and mixed homogeneously with the atmospheric gas.

Evidence for a correlation between features observed in simul­taneous infrared (8-14 µm) and ultraviolet (0.36 µm) images has been found. The sense of the correlation is such that bright UV markings correspond to bright (warm) IR features, and similarly, dark UV markings correspond to dark (cool) IR features. This result implies that dark UV clouds are higher or denser than the bright regions.

Thesis Files