Radar signal return from near-shore surface and shallow subsurface features, Darien Province, Panama
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Hanson, B. C.↗
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Geophysical subsurface probing with radio-frequency interferometry
The radio-frequency interferometry method can be used to probe interiors of celestial bodies and terrestrial areas with low conductivity. In order to interpret the interference patterns, a theoretical study is made of the electromagnetic fields due to a dipole antenna on the surface of a horizontally stratified n-layered medium. Three approaches are used to calculate the interference patterns: direct numerical integration, asymptotic evaluation by the saddle point method, and a residue series approach. The asymptotic approach leads to the geometrical-optics interpretation. The residue approach leads to modal analysis. The validity of the formulation is checked by comparisons with analog model tank experiments and actual field data obtained from glaciers.
Kong, J. A.↗
JPL field measurements at the Finney County, Kansas, test site, October 1976: Meteorological variables, surface reflectivity, surface and subsurface temperatures
Data collected at the Finney County, Kansas test site as part of the Joint Soil Moisture Experiment (JSME) are presented here, prior to analysis, to provide all JSME investigators with an immediate source of primary information. The ground-truth measurements were taken to verify and complement soil moisture data taken by microwave and infrared sensors during aircraft overflights. Measurements were made of meteorological variables (air speed, temperature, relative humidity, and rainfall), surface reflectivity, and temperatures at and below the surface.
Kahle, A. B.↗
Shuttle LESS subsurface attack investigation
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Mcginnis, F. K.↗
Analysis of two-dimensional incompressible flows by a subsurface panel method
A new approach to panel methods is explored for two-dimensional steady incompressible flows. The method uses linear distributions of sources and vortices on straight-line panels, but satisfies boundary conditions on the actual body surface, at nodes that are also end points of the panels. The result is continuity in body-surface velocity distribution, without recourse to numerical quadrature for the velocity influence coefficients. The method is unusually sensitive to the distribution of the nodes. For example, it almost always fails to give acceptable results when the nodes are distributed randomly. However, the continuity of the velocity distribution makes possible a unique node redistribution scheme, which may be iterated to give accurate results reliably.
Moran, J.↗
Martian fresh crater depths - More evidence for subsurface volatiles
The paper presents and examines new depth data, which have greater accuracy and area coverage than those acquired previously, for fresh Martian craters through shadow measurements on high quality Viking Orbiter photography. Consideration is given to these data in the context of similar measurements of lunar and Mercurian craters, noting that most craters studied are shallower than those on the Moon and Mercury. Finally, processes are described which could account for the observed interior morphometries.
Cintala, M. J.↗
Millimeter wave radiometry as a means of determining cometary surface and subsurface temperature
Thermal emission spectra for a variety of cometary nucleus models were evaluated by a radiative transfer technique adapted from modeling of terrestrial ice and snow fields. It appears that millimeter wave sensing from an interplanetary spacecraft is the most effective available means for distinguishing between alternate models of the nucleus and for evaluating the thermal state of the layer which is below the instantaneous surface where modern theories of the nucleus indicate that sublimation of the cometary volatiles actually occurs.
Hobbs, R. W.↗
Variations in interior morphology of 15-20 km lunar craters - Implications for a major subsurface discontinuity
Craters vary in morphology as a function of crater diameter, age, and mode of origin. This study concentrates on the morphology of young lunar impact craters within a limited size range. Elimination of morphologic variations generally attributed to crater size or age leaves a small population which should nearly reflect the varying properties of the lunar substrate. The sample consists of 17 craters 15-20 km in diameter with both simple and complex morphologies. While depth/diameter ratios do not obviously differ between mare and highland subsets, apparent depth, rim height, and profile data do differ distinctly. Highland craters tend to be deep, simple, and bowl-shaped. Mare craters tend to be shallow and flat-floored. Rim heights of complex mare craters are typically greater than those of simple craters. Differences of highland and mare crater morphologies are attributed to variations in the thickness of the lunar megaregolith. Highland craters in this size range do not penetrate the megaregolith. The depth and morphology of complex craters are controlled by the discontinuity at the transition from highly brecciated megaregolith to more coherent crystalline material of the upper crust.
De Hon, R. A.↗
Five-minute oscillations as a subsurface probe of sunspot structure
Observations of the sun which revealed the presence of oscillations due to the 5-min p-modes in the quiet atmosphere are reported. Umbral oscillations with a 145-190 sec period were detected, along with penumbral waves with a 180-250 sec period. The waves have been linked to resonant magneto-atmospheric wave modes in the sunspot atmosphere. The observations were made with a vacuum tower telescope and echelle spectrograph at Sacramento Peak Observatory. Results are presented of the Fe gamma 6,302.5 line. Irregularities in the umbral structures as to which p-mode initiated the activity are taken as evidence that the oscillations are related to activities in sunspot structure below the solar surface. It is shown that the occurrence of three successive p-mode crossings by the oscillations may be valuable for probing the effective depth of a sunspot.
Thomas, J. H.↗
Subsurface valleys and geoarcheology of the eastern Sahara revealed by Shuttle radar
Previously unknown buried valleys, geologic structures, and possible Stone Age occupation sites have been revealed through the Shuttle Imaging Radar (SIR-A) penetration of the extremely dry Selima Sand Sheet, dunes and drift sand of the eastern Sahara. Radar penetration of dry sand and soils varies with the wavelength of the incident signals, which is 24 cm for the SIR-A system, as well as incidence angle and electrical properties of the material which are largely determined by moisture content. The calculated depth of radar penetration of dry sand and granules has been established to be 5 m on the basis of laboratory measurements of Selima Sand Sheet sample electrical properties. September 1982 field studies in Egypt have verified SIR-A signal penetration depths of at least 1 m in the Selima Sand Sheet and drift sand, and 2 m or more in sand dunes.
Mccauley, J. F.↗
Attempt to measure the solar subsurface velocity
Five-minute oscillation modes are advected by horizontal velocities below the solar surface, and thus can be used as probes of rotation and large-scale convective flows. Results of inverse theory applied to observations of high-degree modes carried out on six separate days reveal variations in horizontal velocities with depth from day to day that may be the result of giant convection cells, through noise in the data makes this interpretation somewhat tentative.
Hill, F.↗
Impact of soil surface and subsurface properties on soil saturated hydraulic conductivity in the semi-arid Walnut Gulch Experimental Watershed, Arizona, USA
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R. Becker↗
SIR-B analysis of the Precambrian shield of Sudan and Egypt: Penetration studies and subsurface mapping
A shuttle imaging radar-B (SIR-B) study is proposed for the Precambrian shield in southeast Egypt and northeast Sudan in an area east of the Nile. The phenomenon of radar penetration of thin, dry eolian/alluvial cover is to be confirmed and quantified. The penetration phenomenon is to be used to map structural and lithologic features. Field work to be done in conjunction with image acquisition is discussed.
Dixon, T. H.↗
Application and calibration of the subsurface mapping capability of SIR-B in desert regions
The penetration capability of the shuttle imaging radar (SIR-B) sensor in desert regions is investigated. Refined models to explain this penetration capability in terms of radar physics and regional geologic conditions are devised. The sand-buried radar-rivers discovered in the Western Desert in Egypt and Sudan are defined. Results and procedures developed during previous SIR-A investigation of the same area are extrapolated.
Schaber, G. G.↗
Permafrost and Subsurface Ice in the Solar System
The properties and behavior of planetary permafrost are discussed with reference to the ability of such surfaces to sustain loads characteristics of spacecraft landing and planetary bases. In most occurrences, water ice is in close proximity to, or in contact with, finely divided silicate mineral matter. When ice contacts silicate mineral surfaces, a liquid-like, transition zone is created. Its thickness ranges from several hundred Angstron units at temperatures near 0 degrees C to about three Angstrom units at -150 degrees C. When soluble substances are present, the resulting brine enlarges the interfacial zone. When clays are involved, although the interfacial zone may be small, its extent is large. The unfrozen, interfacial water may amount to 100% or more weight at a temperature of -5 degrees C. The presence of this interfacial unfrozen water acts to confer plasticity to permafrost, enabling it to exhibit creep at all imposed levels of stress. Nucleation processes and load-bearing capacity are examined.
Anderson, D. M.↗
Raman lidar for the remote measurement of subsurface ocean parameters
The Raman lidar technique was developed for the remote measurement of temperature and salinity profiles. A temperature accuracy of 0.5 degrees Centigrade is attainable in a practical field system for depths of up to 3 diffuse attentuation lengths, which can be 100 meters or more in the open ocean. In this paper field test results are reviewed and performance specifications for typical Raman lidar systems are presented.
Leonard, D. A.↗
Nondestructive SEM for surface and subsurface wafer imaging
The scanning electron microscope (SEM) is considered as a tool for both failure analysis as well as device characterization. A survey is made of various operational SEM modes and their applicability to image processing methods on semiconductor devices.
Propst, Roy H.↗
Distribution and state of H2O in the high-latitude shallow subsurface of Mars
The state and distribution of H2O molecules at high latitudes are evaluated numerically with emphasis on the effects of seasonal temperatures on the kinetics of H2O transport. The investigation is carried out with a thermal model for the regolith regions from the surface through the ice interface and an atmospheric model for the H2O vapor density at the surface as a function of latitude. Few differences are found in the state and distribution of H2O whether the regolith is composed of Montmorillonite or basalt. During an obliquity cycle, the average exchanged H2O mass is determined to be in the range 1-20 gr/sq cm over the planetary surface, with a total maximum exchanged volume of 1500 cu km of H2O. The exchanged mass would arise mainly from ground ice in the case of a basalt regolith and from adsorbed H2O with Montmorillonite. Finally, seasonal ice stabilization is expected to occur at latitudes above 40 deg when obliquities exceed 25 deg.
Zent, A. P.↗