Engineering topics

Saunders, R. S.

Publications and source records attributed to Saunders, R. S..

At least 109 records · Page 6

NASA NTRS1982

Tectonic history of the Tharsis region, Mars

The faults of the Tharsis region of Mars have been mapped and delineated on the basis of age. The orientation of each group of faults was analyzed to determine if they were radial to a point. The results indicate that there are at least four discrete centers of faulting within the Tharsis area which are of significantly different age. The four centers proposed are, from oldest to youngest, (1) in the Thaumasia highlands, (2) in northern Syria Planum, and finally, (3) and (4) near Pavonis Mons. While episodes 3 and 4 occupy the same geographic position, they are separated in time by the development of the Tharsis lava plains and shields. Each episode of tectonism was separated from the next by a period of major basaltic volcanism. The tectonic features of the Tharsis area are thus viewed as being the cumulative result of the superposition of several discrete episodes of faulting, rather than the result of one episode about a single point.

Plescia, J. B.↗

NASA NTRS1982

Seasonal carbon dioxide exchange between the regolith and atmosphere of Mars - Experimental and theoretical studies

CO2 penetration rate measurements have been made through basalt-clay soils under conditions simulating the penetration of the cap-induced seasonal CO2 pressure wave through the topmost regolith of Mars, and results suggest that existing theoretical models for the diffusion of a gas through a porous and highly adsorbing medium may be used to assess the importance of the Martian seasonal regolith-atmosphere CO2 exchange. The maximum effect of thermally driven exchange between the topmost seasonally (thermally) affected regolith and the atmosphere shows that, while this may be of greater importance than the isothermal exchange, the thermally driven exchange would be recognizable only if the pressure wave from CO2 exchanged at high latitudes did not propagate atmospherically faster than the rate at which the exchange itself occurred. This is an unreasonable assumption.

Fanale, F. P.↗

NASA NTRS1982

Mars - The regolith-atmosphere-cap system and climate change

A model is derived for the prediction of the Martian regolith-atmosphere-cap CO2 regime's behavior, as well as for the description of the roly of the regime in climate change, through descriptions of the time-temperature histories of 90 regolith 'chunks' on a latitude-depth grid. The influence of differences in regolith adsorption laws for basalt and clay, and the influence of variations in regolith depth with (1) latitude, (2) regolith thermal diffusivity, and (3) total exchangeable CO2 inventory on predicted variations in atmospheric pressure and cap mass, are examined. It is found that the atmosphere acts as a low capacity conduit between two reservoirs through which 10-100 times the current atmospheric mass of CO2 flows. The exchange between the reservoirs is driven by obliquity variations, with the polar cap the dominant CO2 sink at low obliquity and the regolith dominating at high obliquity.

Fanale, F. P.↗

NASA NTRS1981

Planetary exploration sensor systems

Most of the instruments that have been used in planetary exploration have been either spectrometers or imaging devices. Instruments of these types are being developed for the Galileo and VOIR (Venus Orbiting Imaging Radar) missions. Galileo will take advantage of new CCD (charge-coupled device) technology, and VOIR will use techniques of synthetic aperture radar developed for Seasat. For determining the macrostructure of mineral resources, the best approach is believed to involve acoustic imaging, essentially a seismic data processing technique. Determinations of microstructure would require a light microscope and an electron microscope. For determining the nature and form of volatiles, a differential scanning calorimeter could be used. To determine the mineral composition, an electron beam microprobe with X-ray fluorescence and spectroscopy would be used.

Saunders, R. S.↗

NASA NTRS1980

Simulation of orbital radar images

The operating parameters for spaceborne synthetic aperture imaging radar systems was addressed in the cost effective manner by using simulation techniques. The use of airborne images, Seasat images, and computer simulation were the first computer simulation of spaceborne radar imagery was analyzed for system definition studies. Analysis of the simulation indicates that incidence angles as small as 30 are useful for general terrain geomorphologic analysis.

Saunders, R. S.↗

NASA NTRS1980

Radar imaging of volcanic fields and sand dune fields: Implications for VOIR

A number of volcanic fields and sand dune fields in the western part of North America were studied using aircraft and Seasat synthetic aperture radar images and LANDSAT images. The capability of radars with different characteristics (i.e., frequency, polarization and look angles was assessed to identify and map different volcanic features, lava flows and sand dune types. It was concluded that: (1) volcanic features which have a relatively large topographic expression (i.e., cinder cones, collapse craters, calderas, etc.) are easily identified; (2) lava flows of different ages can be identified, particularly on the L-band images; and (3) sand dunes are clearly observed and their extent and large scale geometric characteristics determined, provided the proper imaging geometry exists.

Elachi, C.↗

NASA NTRS1980

Radar altimetry of South Tharsis, Mars

The paper discusses Martian altitudes measured by radar during the oppositions of 1971 and 1973 using the 64-m antenna at Goldstone, Calif. The resultant topographic profiles substantiate a zonal classification of the volanic flows blanketing the south flanks of Arsia Mons, and they confirm the existence of a secondary, parasitic shield, attached from the SSW to the main Arsia shield. The secondary shield is about 400 km in diameter at its base and at least 4 km high at its center. The distribution and orientation of the lunar mare - like ridges in Sinai Planum appear to be independent of the regional gradients. Segments of the chaotic terrain at the eastern terminus of Valles Marineris are located down to 6 km below the level of the surrounding plains.

Roth, L. E.↗

NASA NTRS1980

Estimation of the thickness of the Tharsis lava flows and implications for the nature of the topography of the Tharsis plateau

An attempt to estimate the thickness of the volcanics which cover the large part of the Tharsis region is reported. Estimates for the thickness of the flows were made using the numerous occurrences of the partially buried craters throughout the region and a relation between the crater diameter and crater rim height. Estimates were made along the southern contact with the heavily cratered terrain in the Phoenicis Lacus and Memnonia quadrangles, and along the northeast contact with older plains units in the Tharsis and Lunae Palus quadrangles. In these distal regions the thickness estimates range from 0 to 600-700 m of lava. This would indicate that only 20-30% of the topography is the result of volcanic construction. If the 20-30% estimate is representative of Tharsis as a whole then lava thickness would reach only 2-3 km near the center of the region. Thus only a small fraction of the topography presently observed can be attributed to units readily identifiable as volcanic. This additional evidence indicates that the model for Tharsis of a pre-existing elevated region of heavily cratered crust, capped by a veneer of volcanics is correct.

Plescia, J. B.↗

NASA NTRS1979

The chronology of the martian volcanoes

The volcanoes of Mars have been divided into three groups based on morphology: basaltic shields, domes and composite cones, and highland patera. A fourth group can be added to include the volcano-tectonic depressions. Using crater counts and the absolute chronology of Soderblom, an attempt is made to estimate the history of the volcanoes. Early in the martian history, about 2.5 b.y. ago, all three styles of volcanoes were active at various locations on the surface. At approximately 1.7-1.8 b.y. ago a transition occurred in the style and loci of volcanic construction. Volcanoes of younger age appear to be only of the basaltic shield group and are restricted to the Tharsis region. This same transition was noted by a change in the style of the basaltic shield group. Older shields were small low features, while the younger shields are significantly broader and taller.

Plescia, J. B.↗

NASA NTRS1977

Geologic interpretation of new observations of the surface of Venus

New radar observations of the surface of Venus provide further evidence of a diverse and complex geologic evolution. The radar bright feature 'Beta' (24 deg N, 85 deg W) is seen to be a 700 km diameter region elevated a maximum of approximately 10 km relative to its surroundings with a 60 x 90 km wide depression at its summit. 'Beta' is interpreted to be a large volcanic construct, analogous to terrestrial and Martian shield volcanoes. Two large, quasi-circular areas of low reflectivity, examples of a class of features interpreted to be impact basins by previous investigators who were without the benefit of actual topographic information, are shown in altimetry maps to be depressions. Thus the term 'basin' can be applied, although we urge a non-genetic usage until more complete understanding of their origin is achieved through analysis of future observations.

Saunders, R. S.↗

NASA NTRS1977

Surface of Venus - Evidence of diverse landforms from radar observations

Radar images seem to indicate that some regions of Venus have remained little altered since a period of intense bombardment similar to that recorded by the many large impact craters on the moon. On the other hand, there is evidence in other regions that Venus has been a geologically active planet, forming diverse landforms, and perhaps rivaling the earth in the breadth of features portrayed on its surface

Malin, M. C.↗

NASA NTRS1977

A TiO2 abundance map for the northern maria

A map of TiO2 abundance for most of the northern maria is presented. The telescopic data base used is the 0.38/0.56-micron ratio mosaic from Johnson et at. (1977). The titanium content has been estimated using the correlation established by Charette et al. (1974). The combination of observational, processing, and calibration errors indicates that the TiO2 map is accurate to + or - 2% (wt% TiO2) for high TiO2 content (more than 5%) and + or - 1% for low values of TiO2. Analysis of the lunar sample and telescopic data suggests strongly that the spectral parameter mapped is sensitive primarily to TiO2 abundance in the range 3-9% and does not correlate directly with iron content. It is suggested, however, that for the low TiO2 mare regions (less than 2-3% TiO2) there may be a relation between the spectral ratio and iron content and that some of the reddest mare areas in the Imbrium region may have low iron contents as well as low titanium abundances.

Johnson, T. V.↗

NASA NTRS1976

The geologic development of Mars - A review

The overall view of Mars has changed from earthlike in the prespacecraft era to moonlike following the flyby missions and finally to a planet with intermediate characteristics. There are many impact craters as on the moon, but tectonic and volcanic features resembling structures on earth are also present. However, there is a lack of evidence for the compressional deformation associated with terrestrial plate tectonics and continental drift. Current analyses indicate that Mars has a differentiated interior with a crust and mantle and perhaps a core. Whenever the nature of interior processes, whether overall mantle expansion, plumes, or full-scale convection, the effects at the surface have been predominantly vertical with formation of broad regions of uplift and depression. One of the results is hemispheric asymmetry with cratered terrain in the south and younger uncratered plains in the north.

Mutch, T. A.↗

NASA NTRS1976

The geology and geophysics of Mars

The current state of knowledge concerning the regional geology and geophysics of Mars is summarized. Telescopic observations of the planet are reviewed, pre-Mariner models of its interior are discussed, and progress achieved with the Mariner flybys, especially that of Mariner 9, is noted. A map of the Martian geological provinces is presented to provide a summary of the surface geology and morphology. The contrast between the northern and southern hemispheres is pointed out, and the characteristic features of the surface are described in detail. The global topography of the planet is examined along with its gravitational field, gravity anomalies, and moment of inertia. The general sequence of events in Martian geological history is briefly outlined.

Saunders, R. S.↗

NASA NTRS1976

The geology of Mars

The book constitutes a topographic/geologic atlas of Mars compiled on the basis of data from the various Mariner missions. A large number of maps has been included which systematically describe the character and distribution of the principal landforms: craters, channels, volcanoes, and faults; also related properties such as albedo, elevation, and wind streaks. Pictures of all the important topographic features have been included. The discussion of the material is carried out with a minimum of technical detail, and Mars is examined within a context of interplanetary comparisons.

Mutch, T. A.↗

NASA NTRS1975

Guide to the use of Mariner images

Planetary imaging from unmanned spacecraft, almost exclusively done by digital systems, is examined. The Mars Mariner 9 television camera, representative of such systems, is considered. Each image consists of 700 lines, each containing 832 picture elements, or pixels. Each pixel contains nine binary bits of information capable of displaying 512 discrete brightness levels. Several problems inherent in television systems are discussed. These include nonuniform target response, residual images, noise, and blemishes. These defects can be removed to some extent by decalibration of the image. The final product is geometrically corrected for camera distortion and photometrically corrected. Several versions of the decalibrated images are available. The most generally useful are the geometrically corrected images with enhanced contrast. The Mariner 10 imaging of Mercury is briefly discussed.

Saunders, R. S.↗

NASA NTRS1975

The isostatic state of Martian topography

As is evidenced by the gravity data, the regional topography of Mars falls into two disctinct age groups. The older group is isostatically compensated at relatively shallow depth. All of our analyses indicate that the younger group is only partly compensated and that the depth of partial compensation is also shallow. The young topography is composed primarily of the Tharsis plateau and the adjacent low areas of Chryse and Amazonis. They appear to have all undergone the same amount of partial compensation, suggesting a comtemporaneous origin. All of the topography is consistent with a model of viscous relaxation in an environment of approximate thermal steady state. The minimum viscosity necessary to explain the partial compensation is 10 to the 27th power P, a value typical of a number of lunar studies. Alternatively, the strength required to support the uncompensated fraction of the topography is similar to strengths determined for the earth and moon.

Phillips, R. J.↗

NASA NTRS1975

Vidicon spectral imaging - Color enhancement and digital maps

A silicon imaging photometer system (SIPS) was used to obtain visible and near-infrared spectral imaging data in four narrow bandpasses (0.38, 0.56, 0.85, and 1.05 microns) for a 400-by-400-km lunar region which includes the Serenitatis-Tranquillitatis border. Three ratio frames were used to make color composites of radio images, and spectral maps based on interactive 'cluster' analysis were produced from four video channels. A low albedo titanium-poor unit occurs near the southern edge of the Serenitatis and south of the basin; this unit appears to postdate the high-titanium dark Tranquillitatis and 'blue-ring' material and may be associated with an Al/Si anomaly noticed in Apollo orbital X-ray data.

Johnson, T. V.↗