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The author has identified the following significant results. A program has been developed to correct geometric distortion of pictures reconstructed from MSS tapes. Coastal vegetation species, land use, water turbidity and current circulation were clearly discernible in Skylab pictures of September 12, 1973. Remarkably high spatial resolution was attained.
High spatial resolution spectrophotometric observations (from 0.6 to 2.0 microns) are used to study the Jovian and Saturnian limb darkening at 0 deg phase angle. The limb-darkening coefficients (k) of the Minnaert function are 1.0 over Jupiter's entire disk and between 0.75 and 0.90 for different latitudes on Saturn. These data are used to derive geometric albedoes (G) for the various belts, zones, spots, and regions observed on Jupiter and Saturn. These values of G and k are in turn used to show that an isotropic scattering model is invalid for Jupiter and that at least an asymmetric scattering function, such as the Euler function, is needed to fit the Jovian data. The Jovian scattering function is found to generally vary between 0.960 (1 + 0.85 cos theta) and 0.994 (1 + 0.42 cos theta) as a function of wavelength and the feature observed. The Saturn geometric albedoes and values of k indicate that Euler's function fails to adequately model the scattering properties of Saturnian clouds; they may be better represented by a cumulus cloud model.
The intensity of emission at 45 micrometers, measured with high spatial resolution along a single crossing of the Venus disk, is presented. On the average, the observed darkening toward the limb varies nearly linearly with the cosine of the emission angle. The brightness temperature, extrapolated to normal emission, is 255 K. The limb darkening curve, interpreted in a linear approximation, implies that the atmosphere is quite opaque, with an absorption coefficient of 0.24 per kilometer. Changes in curvature present in the limb darkening curve suggest the existence of thermal inhomogeneities with scale comparable to that of the dark markings shown by ultraviolet images.
A new X-ray image intensifier is described. The device should eventually have a quantum efficiency which is an order of magnitude greater than that of presently available high spatial resolution X-ray detectors, such as microchannel plates. The new intesifier is based upon a GaAs crystal photocathode which is activated to achieve negative electron affinity. Details concerning the detector concept are discussed together with the theoretical relations involved, X-ray data, and optical data.
A program for measuring polarization of Venus photographically to obtain high spatial resolution has been carried out. Average values of polarization of the disk are compared with those of Dollfus and Coffeen. Trends and errors in spatial mapping are discussed.
Results of an experiment to search for absorption of the soft diffuse X-ray background by M31, the Andromeda Nebula, are presented. Both X-ray and 21-cm observations were obtained with high spatial resolution; the X-ray detector had a 2-degree field of view, and the 21-cm data were taken with 20-minute resolution. The results establish that at least 48 percent of the soft X-ray flux has a local source, but that the remainder may be of distant origin and therefore of cosmological significance.
The relation of aereal extent of snow cover to the average monthly runoff in a given watershed was investigated by comparing runoff records with a series of snowcover maps. Studies using the high spatial resolution available with ERTS-1 imagery were carried out for the Wind River Mountains watersheds in Wyoming, where it was found that the empirical relationship varied with mean elevation of the watershed. In addition, digital image enhancement techniques are shown to be useful for identifying glacier features related to extent of snowcover, moraine characteristics, and debris average. Longer wavelength observations using sensors on board the Nimbus 5 Satellite are shown to be useful for indicating crystal size distributions and onset of melting on glacier snow cover.
High-spatial-resolution images of Venus were obtained at wavelengths between 8 and 14 microns when the planet was at a phase angle of 112 deg with the morning terminator in view. The images confirm the existence of a previously mapped flux anomaly near the south pole and show evidence of other infrared features, presumably transient in nature. Flux differences of 2-7% were measured, corresponding to brightness temperature variations of roughly 1-3 K. The images also confirm the difference between polar and equatorial limb darkening. Finally, evidence is presented for a night-day asymmetry in the flux, with the brightness temperature greater by about 2 K on the sunlit side.
The surface emissivity and reflectivity of soil are strong functions of its moisture content. Changes in emissivity, observed by passive microwave techniques (radiometry), and changes in reflectivity, observed by active microwave techniques (radar), can provide information on the moisture content of the 0 to 5 cm surface layer. In addition, the thermal inertia of the surface layer, which can be remotely sensed by observing the diurnal range of surface temperature, is an indicator of soil moisture content. The thermal infrared approach to remote sensing of soil moisture has little utility in the presence of cloud cover, but provides soil moisture data at high spatial resolutions and thermal data which are a potentially useful indicator of crop status. Microwave techniques can penetrate cloud covers. The passive technique has been demonstrated by both aircraft and spacecraft instruments, but spatial resolution is limited by the size of the antenna which can be flown. Active microwave systems offer the possibility of better spatial resolution, but have yet to be demonstrated from aircraft or spacecraft platforms.
A position-sensitive event-counting electronic readout system for microchannel plates (MCPs) is described that offers the advantages of high spatial resolution and fast time resolution. The technique relies upon a four-quadrant electron-collecting anode located behind the output face of the microchannel plate, so that the electron cloud from each detected event is partly intercepted by each of the four quadrants. The relative amounts of charge collected by each quadrant depend on event position, permitting each event to be localized with two ratio circuits. A prototype quadrant anode system for ion, electron, and extreme ultraviolet imaging is described. The spatial resolution achieved, about 10 microns, allows individual MCP channels to be distinguished.
From 5-micron high-spatial-resolution images of Jupiter, flux-frequency histograms of the equatorial region show a trimodal distribution of brightness temperatures. Combined with limb-darkening measurements, a three-layer cloud model for Jupiter is developed. The highest, coldest clouds, apparently homogeneous and displaying relatively little limb darkening, cover the zones. These clouds are not present over the belts, allowing observational access to deeper regions. The belts appear heterogeneous: small, localized hot areas show enhanced limb darkening, while much of the belt is distinctly cooler and exhibits shallower limb darkening. These belt properties can be explained by a cool emitting layer superposed upon a hot, dense cloud deck.
High-spatial-resolution images of Jupiter were produced on the Hale 200-in. telescope. A programmable wobbling secondary was used to raster-scan the planet with 64 by 64 1-arcsec pixels. Images were made with broadband (8-14 microns) and several 1- and 2-micron-wide filters. All images reveal a belt-and-ozone structure similar to visible photographs. Belts in the broadband data appear to be about 2 K hotter than zones, but contrast varies markedly in different parts of the 8-14-micron spectral region. The lowest belt-zone contrast is found in the hydrogen-opacity-dominated region at 12.5 microns, while images at 9.5 microns exhibit the greatest contrast. Isolated areas are observed to be as much as 4 K hotter than surrounding areas at 9.5 microns. This large contrast is probably due to variations in the distribution of the ammonia clouds in the upper atmosphere.
Jupiter was observed in six continuum wavelength channels in the region 4100-8300 A, using a silicon vidicon imaging photometer. Spectral reflectivities and high spatial resolution limb-darkening curves for several belts and zones have been extracted from the data. Simple model fits to the data yield information regarding spectral and spatial variations in single-scattering albedos and shape of particle single-scattering phase functions. Belts appear to be more backscattering than zones, particularly in the blue. The data are in moderate agreement with limb-darkening predicted by models derived from the center-to-limb variation in equivalent width of the H2 4-0 S(1) quadrupole line (Cochran, 1976) in the South Tropical Zone, but strongly disagree with the results of such models for the North Equatorial Belt.
High-spatial-resolution observations of S140 are presented at wavelengths from 35 to 175 microns. A single strong far-infrared source has been found coincident with a compact near-infrared and H2O maser source and the center of a molecular cloud. The far-infrared spectrum suggests either significant absorption in the 20-micron region or a two-temperature dust structure. The infrared luminosity of approximately 20,000 suns is comparable to that of a late O or early B star, although no radio continuum flux has been seen from this object. The source is quite likely a dust-embedded protostar.
During the last 10 years, infrared astronomy, based on observations in the wavelength range from 2 to 1000 micrometers, has become a major field of observational astrophysics. This development is mainly related to two major technical advances. Extremely sensitive detectors have been developed and become available for astronomical applications. Motivated by the first development, major groups have expended much effort in building and operating telescopes above most or all of the earth's atmosphere in order to circumvent its opacity and emission throughout the range. Attention is given to advances in the area of infrared detectors, platforms for infrared astronomy, focal plane instruments, high spatial resolution instrumentation, and infrared polarization measurements.
A coordinated program to observe Jupiter at high spatial resolution in the 5-micrometer wavelength region was undertaken to support Voyager 1 imaging and infrared radiation experiment targeting. Jupiter was observed over a 5-month period from Palomar and Mauna Kea observatories. The frequency of observations allowed the selection of interesting areas for closer Voyager examination and also provided good short-term monitoring of variations in cloud morphology. Significant global changes in the 5-micrometer distribution are seen over this time period.
The topology of lunar remanent fields is investigated by analyzing simultaneous magnetometer and solar wind spectrometer data. The diffusion model proposed by Vanyan (1977) to describe the field-plasma interaction at the lunar surface is extended to describe the interaction with fields characterized by two scale lengths, and the extended model is compared with data from three Apollo landing sites (Apollo 12, 15 and 16) with crustal fields of differing intensity and topology. Local remanent field properties from this analysis are compared with high spatial resolution magnetic maps obtained from the electron reflection experiment. It is concluded that remanent fields over most of the lunar surface are characterized by spatial variations as small as a few kilometers. Large regions (50 to 100 km) of the lunar crust were probably uniformly magnetized early in the evolution of the crust. Smaller scale (5 to 10 km) magnetic sources close to the surface were left by bombardment and subsequent gardening of the upper layers of these magnetized regions. The small scale sized remanent fields of about 100 gammas are measured by surface experiments, whereas the larger scale sized fields of about 0.1 gammas are measured by the orbiting subsatellite experiments.
High-spatial-resolution (a few seconds of arc) observations of microwave bursts have demonstrated that only the impulsive phase of the burst is polarized; one observes only one polarity in the burst source if it is weak (Alissandrakis and Kundu) and both polarities if it is intense (Enome et al.). These results are interpreted in terms of an asymmetrical bipolar field structure of the loop in which the energetic electrons responsible for the radiation are contained. The role of unequal field strengths at the feet of the loop on the number of electrons trapped and their pitch angle distribution are discussed in a specific model. Computations of the polarized intensity originating from each foot of the loop seem to be consistent with the observations at present available.