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Zisk, S. H.

Publications and source records attributed to Zisk, S. H..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Valley systems on Tyrrhena Patera, Mars - Earth-based radar measurements of slopes

The presently treated eight topographic profiles across the Martian volcano Tyrrhena Patera indicate that the vocano rises about 1.5 km above the plains of Hesperia Planum to the east, and exhibit an average height/diameter ratio of about 1:340. The slopes of the northern flank of Tyrrhena Patera bear little correlation with the width or depth of valley systems in that area, suggesting that erosion by gravity-driven flows was not responsible for valley formation. Attention is given to such other valley geometry and location controlling factors as ground-water release variations and volcano surface unit materials' strength differences.

Zisk, S. H.↗
NASA NTRS1992

Estimating Lunar Pyroclastic Deposit Depth from Imaging Radar Data: Applications to Lunar Resource Assessment

Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits.

Campbell, B. A.↗
NASA NTRS1991

New studies of Martian volcanoes

To investigate the morphology, topography, and evolution of volcanic constructs on Mars, researchers have been studying the volcanoes Olympus Mons, Tyrrhena Patera, and Apollinaris Patera. These studies relied upon the analysis of digital Viking orbiter images to measure the depth and slopes of the summit area of Olympus Mons, upon new Earth-based radar measurements for the analysis of the slopes of Tyrrhena Patera, and upon the color characteristics of the flanks of Apollinaris Patera for information regarding surface properties.

Mouginis-Mark, P. J.↗
NASA NTRS1990

The Alphonsus region - A geologic and remote-sensing perspective

A number of interesting questions exist concerning the composition and origin of a number of geologic units in the west-central highlands crater Alphonsus. This paper utilizes a variety of newly obtained remote sensing data to address these questions and improve the current understanding of the geologic history of the Alphonsus region. Near-infrared and UV/VIS reflectance spectra were obtained and analyzed for many of the geologic features, the results of which are presented here. Spectra collected for pyroclastic debris associated with three endogenic dark halo crater complexes on the floor of Alphonsus indicate a basaltic assemblage rich in olivine. These pyroclastic deposits exhibit generally low returns on the depolarized 3.8 cm radar image. An exogenic dark halo crater was identified on the interior of Alphonsus and appears to be composed of a mixture of pyroclastic debris and highlands material. The light plains deposits and other highland units in the Alphonsus region generally exhibit a noritic compostion. However, the Alphonsus central peak is composed of pure anorthosite. This composition is unique within the region.

Coombs, C. R.↗
NASA NTRS1989

Radar scattering mechanisms within the meteor crater ejecta blanket: Geologic implications and relevance to Venus

Simple impact craters are known to occur on all of the terrestrial planets and the morphologic expression of their ejecta blankets is a reliable indicator of their relative ages on the Moon, Mars, Mercury, and most recently for Venus. It will be crucial for the interpretation of the geology of Venus to develop a reliable means of distinguishing smaller impact landforms from volcanic collapse and explosion craters, and further to use the observed SAR characteristics of crater ejecta blankets (CEB) as a means of relative age estimation. With these concepts in mind, a study was initiated of the quantitative SAR textural characteristics of the ejecta blanket preserved at Meteor Crater, Arizona, the well studied 1.2 km diameter simple crater that formed approx. 49,000 years ago from the impact of an octahedrite bolide. While Meteor Crater was formed as the result of an impact into wind and water lain sediments and has undergone recognizable water and wind related erosion, it nonetheless represents the only well studied simple impact crater on Earth with a reasonably preserved CEB. Whether the scattering behavior of the CEB can provide an independent perspective on its preservation state and style of erosion is explored. Finally, airborne laser altimeter profiles of the microtopography of the Meteor Crater CEB were used to further quantify the subradar pizel scale topographic slopes and RMS height variations for comparisons with the scattering mechanisms computed from SAR polarimetry. A preliminary assessment was summarized of the L-band radar scattering mechanisms within the Meteor Crater CEB as derived from a NASA/JPL DC-8 SAR Polarimetry dataset acquired in 1988, and the dominant scattering behavior was compared with microtopographic data (laser altimeter profiles and 1:10,000 scale topographic maps).

Garvin, J. B.↗
NASA NTRS1985

The nature of crater rays - The Copernicus example

It is pointed out that crater rays are filamentous, generally high-albedo features which emanate nearly radially from young impact structures. An investigation has been conducted of the physical and chemical properties of a single lunar ray system for Copernicus crater with the objective to achieve a better understanding of the nature of crater rays, taking into account questions regarding the local or foreign origin of ray material. A combination of data is considered, giving attention to spectral reflectance (for composition), radar (for physical properties), and images (for photogeologic context). The crater Copernicus was selected because of its well-developed ray system, the crater's relative youth, and the compositional contrast between the target material of Copernicus crater and the material on which many rays were emplaced.

Pieters, C. M.↗
NASA NTRS1985

Venus global radar reflectivity and correlations with elevation

A geological analysis of the global radar reflectivity data for Venus is presented. The statistical and map pattern distribution of the radar reflectivity rho is first analyzed in the context of the porosity structure of the surface. Rho is then correlated with elevation in order to examine the degree of topographic control on material properties which could depend on PT-sensitive chemical weathering phenomena. Comparison of the rms slope alpha and rho correlations with elevation demonstrates that there are distinct topographic zones defined on the basis of the rho and alpha trends. Finally, hierarchical clustering analysis is applied to the global rho, alpha, and 100-km baseline regional slope data sets in order to define radar property-related subregions.

Garvin, J. B.↗
NASA NTRS1985

Surface characteristics of Venus derived from Pioneer Venus altimetry, roughness, and reflectivity measurements

Pioneer Venus data sets for global topography, surface roughness, and reflectivity are analyzed, and the geological significance of some of the distinctive surface types is locally calibrated by examining high-resolution images from the Venera lander spacecraft and the Arecibo Observatory. Regional rock and bedrock surfaces are found to cover the majority of the planet. The relatively smooth rock and bedrock surfaces probably represent lava flows. Porous and unconsolidated fine materials cover less than about 27 percent of the surface. The distribution of soil surfaces indicate that they are the result of local weathering and small amounts of lateral transport. Several hypotheses for the origin of the high-dielectric materials which cover a small portion of the surface are discussed.

Head, J. W., III↗
NASA NTRS1985

Structure of terrestrial impact craters from SIR-B radar data - Preliminary results

The structure in and around the Charlevoix and Deep Bay impact craters was analyzed by comparing SIR-B radar image lineament maps with maps derived from Landsat data and aerial photography. Relationships revealed include the discovery in the Deep Bay lineament distribution of a mode, of slightly different location and size to that determined by aerial photography, which correlates with the regional glacial trend. The Deep Bay regional glacial trend displays a much more prominent signature in the aerial photography than in the radar data, confirming the influence of radar look direction on the interpretation of lineament distribution and orientation. Effects from the impact event are noted in the radar images of both craters, with lineaments of one km or less appearing to be associated with the rim structure.

Fisher, P. C.↗
NASA NTRS1984

Geological, structural, and geomorphological analyses from SIR-B

A Shuttle Imaging Radar-B (SIR-B) study designed to develop a better understanding of the application of radar in geological studies is described. The specific objectives for deltaic environments include the examination of delta morphology and the intertidal zone, the surface expression of shallow bathymetry, the characterization of vegetation cover, and the water balance of the delta. In impact crater environments, the goals include the establishment of the radar characteristics of exposed craters and the application of this knowledge to test for the detectability of very poorly exposed craters.

Head, J. W., III↗
NASA NTRS1984

Evaluation of the L-band scattering characteristics of volcanic terrain in aid of lithologic identification, assessment of SIR-B calibration, and development of planetary geomorphic analogs

The objectives of the Shuttle Imaging Radar-B (SIR-B) scattering study and calibration investigation of volcanic terrain are to delineate textural and structural features, to evaluate the L-band scattering characteristics, and to assess SIR-B calibration. Specific tasks are outlined and expected results are summarized.

Kaupp, V. H.↗
NASA NTRS1984

Hypsometric studies of Mars.

Altitude data derived from the 12.6 cm radar measurements obtained at JPL's Goldstone Facility were used to explore the utility of this type of regional analysis and to develop criteria for the interpretation of hypsometric data for planets where no visual images are available. Examination of the radar-derived hypsogram for Mars shows that the unimodal distribution of elevations contains several second order peaks and is skewed toward a modal elevation of about 3.5 km above the 6.1 mb datum. Individual topographic features can be recognized from this hypsogram, but such interpretations are based on the known surface morphology that has been determined from spacecraft images. It is not yet known how, for example, cratered terrain, regional slopes or other morphological features could be identified using the hypsogram if no images were available for ground-truth. The role that large impact craters play in influencing the shape of a hypsogram is being studied.

Blake, P. L.↗
NASA NTRS1982

New radar-derived topography for the northern hemisphere of Mars

Earth-based radar altimetry data for the northern equatorial belt of Mars (6 deg S-23 deg N) have recently been reduced to a common basis corresponding to the 6.1-mbar reference surface. A first look at these data indicates that the elevations of Tharsis, Elysium, and Lunae Planum are lower (by 2-5 km) than has been suggested by previous estimates. These differences show that the required amount of tectonic uplift (or constructional volcanism) for each area is less than has been previously envisioned. Atmospheric or surficial conditions are suggested which may explain the discrepancies between the radar topography and elevations measured by other techniques. The topographies of Chryse Planitia, Syrtis Major, and Valles Marineris are also described.

Downs, G. S.↗
NASA NTRS1982

Mars: Definition and characterization of global surface units with emphasis on composition

Viking 2 approach maps of red and violet normal albedo are used to define units of similar optical properties for a large area of the Martian surface. Computer processing of these data reveals clusters of albedo values relating to specific, contiguous regions of the planet, with some unit boundaries being of a gradational nature while others are more discrete. A study of the albedo properties of analog materials measured in the laboratory, and of telescopic spectrophotometry of Mars, indicates that both hydroxylated and hematitic oxidized materials exist on the surface. The most probable surface expression of global dust and/or high albedo soils is in the classical bright region, Arabia. Most low albedo features in the region studied have red and violet albedos that are consistent with a dark substrate, such as basalt, coated by, or mixed with, a fine grained alteration product.

Mccord, T. B.↗
NASA NTRS1982

Ancient and modern slopes in the Tharsis region of Mars

Ancient slope directions in the Martian Tharsis region are compared with new earth-based radar observations in an effort to detect tectonic deformations. Data were taken from 20-150 pixel/m Viking Orbiter images and from 200 m orthophotomosaics prepared by the U.S. Geological Survey. The positions of 475 lava flows were determined, covering widths between 5-10 km on higher slopes and 15-35 km on lower slopes. Most of the flows originated from four volcanos, although none issued from Olympus Mons, which makes up the central portion of the Plateau. Further radar-derived topography was made of, Arsia Mons and Syria Planum in latitudes 14-21 deg S to find differences in regional gradients and the lava flow directions, to determine if deformations occurred after the lava flows. A lithospheric stability is concluded, indicating no tectonic upheavals since the days of Tharsis Plateau volcanic activity.

Mouginis-Mark, P. J.↗
NASA NTRS1981

Lunar craters with radar bright ejecta

The properties of the 3.8-cm radar-bright halos observed around certain lunar impact craters are compiled and compared with 70-cm radar, thermal infrared and photogeological data in order to address the nature of the halos. Diameters, positions, and radar and IR signal strengths are presented for 120 radar-bright ejecta regions of size greater than 20 km and twice the diameter of the crater. The 3.8-cm halos are noted to range in size up to 30 times that of the crater itself, although the strength of the signal from the crater and rim lies in a narrow range, while the IR halos are smaller in extent and variable in signal strength. The radar-bright ejecta are found to have a range of optical properties, and to be associated with fresh primary impact craters. Data are thus consistent with craters having radar-bright ejecta deposits having ages of less than 10 million to 1 billion years, with the radar and infrared signatures of the ejecta deposits produced by combinations of enhanced blockiness and roughness.

Thompson, T. W.↗
NASA NTRS1980

Anomalous region on Mars - Implications for near-surface liquid water

An anomalous region has been identified on Mars from the 1971 and 1973 earth-based Goldstone radar data. This region is characterized by coincident very high radar reflectivities and unusual smoothness. Very few realistic surface morphologies can generate such return-signals. Liquid water within about 50-100 cm of the surface is one possibility, an interpretation strengthened by an apparent seasonal variation in surface reflectivity for the same locality.

Zisk, S. H.↗