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  • 1
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    Topography of closed depressions, scarps, and grabens in the north Tharsis region of Mars: Implications for shallow crustal discontinuities and Graben formation (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Using Viking Orbiter images, detailed photoclinometric profiles were obtained across 10 irregular depressions, 32 fretted fractures, 40 troughs and pits, 124 solitary scarps, and 370 simple grabens in the north Tharsis region of Mars. These data allow inferences to be made on the shallow crustal structure of this region. The frequency modes of measured scarp heights correspond with previous general thickness estimates of the heavily cratered and rigded plains units. The depths of the flat-floored irregular depressions (55-175 m), fretted fractures (85-890 m), and troughs and pits (60-1620 m) are also similar to scarp heights (thicknesses) of the geologic units in which these depressions occur, which suggests that the depths of these flat-floored features were controlled by erosional base levels created by lithologic contacts. Although the features have a similar age, both their depths and their observed local structural control increase in the order listed above, which suggests that the more advanced stages of associated fracturing facilitated the development of these depressions by increasing permeability. If a ground-ice zone is a factor in development of these features, as has been suggested, our observation that the depths of these features decrease with increasing latitude suggests that either the thickness of the ground-ice zone does not increase poleward or the depths of the depressions were controlled by the top of the ground-ice zone whose depth may decrease with latitude.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 114; 2; p. 403-422
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  • 2
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    Rapid extraction of relative topography from Viking orbiter images. 2: Application to irregular topographic features (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-06
    Description: The ratio and flat field photoclinometric methods for determining crater form topography are described. Both methods compensate for the effects of atmospheric scattering by subtracting a haze value from all brightness values. Algorithms were altered to derive relative topographic data for irregular features such as ejecta blankets, lava flows, graben and ridge scarps, dune forms, and stratified materials. After the elevations along the profiles are obtained by integration of the photometric function, a matrix transformation is applied to the image coordinates of each pixel within each profile, utilizing each pixel's integral height, to produce a projection of each profile line onto the surface. Pixel brightness values are then resampled along the projected track of each profile to determine a more correct height value for each pixel. Precision of the methods is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Rept. of Planetary Geology Program, 1983; p 263-265
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  • 3
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    Characterization of surficial geologic units on Venus from Pioneer Venus radar data: A progress report (1984)
    In:  CASI
    Details
    Publication Date: 2006-04-06
    Description: A classification database using the reflectivity (derived from the altimetry data), rms slope, and the first principal component of altimetry and topographic slope is presented. The resultant clustered data is examined qualitatively as well as quantitatively, to establish the statistical integrity of each cluster by use of an interactive, ternary plotting algorithm. This algorithm plots, for a cluster, the position of each of its pixels within a ternary diagram whose apices represent reflectivity, rms slope, and the first principal component. The digital values in these three databases are normalized such that unity is represented by a value of 255 in each database. The frequencies of each plotted point within the ternary diagram are recorded in order to establish the mode of each cluster. The pixels of each cluster are displayed as one separate color; their ternary plot will show not only the interrelations between clusters, but also the presence of any anomalous points within a cluster. Existing lunar and terrestrial analog radar data is used to establish fields within this ternary diagram that are indicative of as many different geologic materials and tectonics settings as possible. The resultant fields are used to determine empirically the geologic significance of the clusters resulting from the cluster analysis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Repts. of Planetary Geol. Program; p 65-66
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  • 4
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    Rheological analyses of lava flows on Mars (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Researchers obtained 183 profiles of lava flows on Mars using photoclinometry. These photoclinometric profiles were leveled by adjusting them until the levee crests or bases had the same elevations (depending on the situation). Here, researchers report some of the results of their analysis of 27 flows on the flanks of Alba Patera (3 flows), near the summit of Ascraeus Mons (6 flows), the flanks of Arsia Mons (3 flows), and the flanks of Olympus Mons (15 flows). Results suggest that the flows examined to date are not felsic or ultramafic; rather, they probably range from basalts to basaltic andesites. Thus, the suggestion that flows on Olympus Mons and elsewhere may be more silicic than Hawaiian basalts is supported by the researchers' results. These suggestions are testable with suitable measurements of silica contents of the flows.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 170-171
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  • 5
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    Interactions of tectonic, igneous, and hydraulic processes in the North Tharsis Region of Mars (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Recent work on the north Tharsis of Mars has revealed a complex geologic history involving volcanism, tectonism, flooding, and mass wasting. Our detailed photogeologic analysis of this region found many previously unreported volcanic vents, volcaniclastic flows, irregular cracks, and minor pit chains; additional evidence that volcanic tectonic processes dominated this region throughout Martian geologic time; and the local involvement of these processes with surface and near surface water. Also, photoclinometric profiles were obtained within the region of troughs, simple grabens, and pit chains, as well as average spacings of pits along pit chains. These data were used together with techniques to estimate depths of crustal mechanical discontinuities that may have controlled the development of these features. In turn, such discontinuities may be controlled by stratigraphy, presence of water or ice, or chemical cementation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 73-74
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  • 6
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    Have graben wall scarps accumulated sand and dust on Mars? (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Grabens are linear fault bounded troughs that are extremely abundant on Mars (about 7000 cover the Western Hemisphere). Analysis of lunar and Martian grabens as well as analogous structures on Earth indicates that grabens form under extension when the crust is pulled apart. On Mars, topographic maps are not of sufficient resolution to measure graben wall slopes. Seismic shaking on Mars might be capable of reducing 60 deg fault scarps to an angle of repose. Some other process must be responsible for further reducing graben wall slopes. If the deposition of sand and dust along graben walls is responsible for their extremely low slopes, then a variety of implications are possible. Sand and/or dust movement and deposition is ubiquitous in grabens over most of Mars, as similar looking grabens are found over the entire Western Hemisphere and this requires a plentiful supply of sand or dust. If the material that accumulates is of low density and cohesion, attempts to traverse graben walls might be difficult. Rimless shallow depressions could be more effective sinks for sand and dust on Mars than has been realized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Ames Research Center, Sand and Dust on Mars; p 20
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  • 7
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    Unsupervised Classification of Global Radar Units on Venus (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-09
    Description: Characterization of the Venusian surface in terms of its radar properties was accomplished by application of an unsupervised, linear discriminant algorithm to two Pioneer-Venus (PV) Orbiter radar data sets: the RMS-slope (surface roughness) and reflectivity. Both databases were spatially filtered to the same effective resolution of 100 km prior to classification. A recent supervised classification study using these data was based on presupposed morphologic significance of selected data ranges. The knowledge of both Venusian geology and the geologic significance of the radar data is so limited that the data warrant a more unsupervised approach; for this study a linear discriminant classifier was chosen. This approach is purely statistical, thereby removing any observer bias. Statistical significance of the resulting clusters was evaluated by an ancillary program in which an F test utilizing the Mahalanobis' distance.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 450-452
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  • 8
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    Martian terrains (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Terrain studies of candidate landing sites for a future rover/sample-return mission to Mars are being conducted to evaluate the geologic and trafficability aspects of each site. An optimum site should have geologic units of widely diverse ages and chemical compositions occurring in close enough proximity and in smooth enough terrain so that a roving vehicle of limited traverse ability (+ or - 100 km) could collect representative samples. In FY 1986, geologic maps were compiled at 1:500,000 and 1:2 million scales of the Mangala Valles, Kasei Valles, Chasma Boreale (north polar), and Planum Australe (south polar) areas, and a study was begun of the topography and surface roughness characteristics of the Mangala Valles site. Geologic mapping has been greatly facilitated by specially enhanced, high-resolution Viking photographs, which clarify stratigraphic relations of units unrecognized earlier. Photoclinometric profiles of topographic features provide width and depth measurements of four classes of channels, the thickness of some volcanic units, and the throw on some faults. Estimates of the surface roughness of units are calculated using a newly developed USGS computer program and using measurements derived from Earth-based radar.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 545-547
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  • 9
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    High frequency dynamic pressure calibration technique (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A high frequency dynamic calibration technique for pressure transducers has been developed using a siren pressure generator (SPG). The SPG is an inlet-area-modulated device generating oscillating waveforms with dynamic pressure amplitudes up to 58.6 kPa (8.5 psi) in a frequency range of 1 to 10 kHz. A description of the generator, its operating characteristics and instrumentation used for pressure amplitude and frequency measurements is given. Waveform oscillographs and spectral analysis of the pressure transducers' output signals are presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 10
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    TIROS radiation measurements and variations in atmospheric heating (1966)
    In:  CASI
    Details
    Publication Date: 2019-05-30
    Description: Tiros VII radiation measurements and variations in atmospheric heating
    Keywords: METEOROLOGY
    Type: NASA-CR-581
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