Engineering topics

Garvin, J. B.

Publications and source records attributed to Garvin, J. B..

At least 73 records · Page 4

NASA NTRS1989

Shuttle imaging radar (SIR-B) investigations of the Canadian Shield - Summary report

The objectives and results of two imaging-radar experiments carried on a Shuttle mission with the purpose of studying the structure of crustal province boundaries and the effects of illumination geometry are reviewed. The primary geological objectives as well as the secondary technique-oriented objective are outlined, along with digital processing techniques. The tectonic relationships of structural provinces are analyzed, and data pertaining to the Kapuskasing Structural Zone is discussed. Fracture patterns and diabase dike swarms are assessed. Focus is placed on the utilization of multiple look directions and incidence angles and on digital image-enhancement techniques such as linear contrast stretch, low-pass filter for speckle reduction, modified Moore-Waltz edge enhancement, and coregistration and display of multiple look azimuths.

Masuoka, P. M.↗

NASA NTRS1988

Geological observation of impact craters on Mars and the earth using remote-sensing methods

It has been suggested that future multispectral and radar remote sensing of Martian craters can be developed on the basis of studies of multispectral and radar signatures of earth craters which are reasonable analogues of the Martian varieties. The present paper is a contribution toward establishing a methodology for detecting the record of very fresh craters on Mars.

Garvin, J. B.↗

NASA NTRS1988

Astronaut's guide to terrestrial impact craters

Impact cratering of the earth's surface is discussed and compared with lunar craters. The basic types found on earth are either simple craters or complex impact structures and basins. Meteorite fragments and shock metamorphism provide evidence of a crater's formation by meteorite impact. Known craters on earth are ordered by location and a few principal facts are given for each crater and the general terrain in which it is located. A satellite picture of each crater and maps identifying crater locations are provided.

Grieve, R. A. F.↗

NASA NTRS1988

A Mars orbital laser altimeter for rover trafficability: Instrument concept and science potential

Limited information on the types of geologic hazards (boulders, troughs, craters etc.) that will affect rover trafficability on Mars are available for the two Viking Lander sites, and there are no prospects for increasing this knowledge base in the near future. None of the instrument payloads on the upcoming Mars Observer or Soviet PHOBOS missions can directly measure surface obstacles on the scales of concern for rover safety (a few meters). Candidate instruments for the Soviet Mars 92 orbiter/balloon/rover mission such as balloon-borne stereo imaging, rover panoramic imaging, and orbital synthetic aperature imaging (SAR) are under discussion, but data from this mission may not be available for target areas of interest for the U.S. Mars Rover Sample Return (MRSR) mission. In an effort to determine how to directly measure the topography of surface obstacles that could affect rover trafficability on Mars, we are studying how to design a laser altimeter with extremely high spatial and vertical resolution that would be suitable for a future Mars Orbiter spacecraft (MRSR precursor or MRSR orbiter). This report discusses some of the design issues associated with such an instrument, gives examples of laser altimeter data collected for Mars analog terrains on Earth, and outlines the scientific potential of data that could be obtained with the system.

Garvin, J. B.↗

NASA NTRS1988

Geological remote sensing signatures of terrestrial impact craters

Geological remote sensing techniques can be used to investigate structural, depositional, and shock metamorphic effects associated with hypervelocity impact structures, some of which may be linked to global Earth system catastrophies. Although detailed laboratory and field investigations are necessary to establish conclusive evidence of an impact origin for suspected crater landforms, the synoptic perspective provided by various remote sensing systems can often serve as a pathfinder to key deposits which can then be targetted for intensive field study. In addition, remote sensing imagery can be used as a tool in the search for impact and other catastrophic explosion landforms on the basis of localized disruption and anomaly patterns. In order to reconstruct original dimensions of large, complex impact features in isolated, inaccessible regions, remote sensing imagery can be used to make preliminary estimates in the absence of field geophysical surveys. The experienced gained from two decades of planetary remote sensing of impact craters on the terrestrial planets, as well as the techniques developed for recognizing stages of degradation and initial crater morphology, can now be applied to the problem of discovering and studying eroded impact landforms on Earth. Preliminary results of remote sensing analyses of a set of terrestrial impact features in various states of degradation, geologic settings, and for a broad range of diameters and hence energies of formation are summarized. The intention is to develop a database of remote sensing signatures for catastrophic impact landforms which can then be used in EOS-era global surveys as the basis for locating the possibly hundreds of missing impact structures. In addition, refinement of initial dimensions of extremely recent structures such as Zhamanshin and Bosumtwi is an important objective in order to permit re-evaluation of global Earth system responses associated with these types of events.

Garvin, J. B.↗

NASA NTRS1987

Comparison of the compositions of Venusian surface rocks with those of the terrestrial ocean floor

A statistical comparison of data on the composition of the Venusian surface obtained with Venera and Vega lander X-ray fluorescence spectrometers and data on the composition of the terrestrial ocean floor indicates that the Venera 14 data correspond to certain thoeiitic basalts of the Kane fracture zone in the Middle-Atlantic ridge (22-25 deg N). It is suggested that deep magma storage regions exist on Venus and that the separation of tholeiitic and alkali magmas from a single primitive parent magma is an important process on Venus.

Garvin, J. B.↗

NASA NTRS1987

Multispectral geologic remote sensing of a suspected impact crater near Al Madafi, Saudi Arabia

A multispectral Landsat TM image of a 6-km-diameter circular formation at Al Madafi in NW Saudi Arabia is interpreted by means of color-band composites, band ratios, and principal-components analysis to determine the nature of this feature. The geological characteristics of impact craters are discussed, and the satellite-image analysis techniques are described. Disruptions in the pattern of spectral signatures are seen in the Al Madafi formation and shown to be consistent with an impact origin.

Garvin, J. B.↗

NASA NTRS1987

Martian surface physical properties to be derived by radar altimeter on the Mars observer spacecraft

The potential is described of a candidate Mars Observer altimeter for determining dielectric properties of Mars regolith. It is pointed out that it is straightforward to use the time between altimeter pulse trains for passive radiometry (hence dielectric properties) and roughness can be derived. Given the mission plan the whole surface can be mapped at least three times, yielding data on seasonal variability.

Garvin, J. B.↗

NASA NTRS1986

The Geoscience Laser Altimetry/Ranging System (GLARS)

The Geoscience Laser Altimetry Ranging System (GLARS) is a highly precise distance measurement system to be used for making extremely accurate geodetic observations from a space platform. It combines the attributes of a pointable laser ranging system making observations to cube corner retroreflectors placed on the ground with those of a nadir looking laser altimeter making height observations to ground, ice sheet, and oceanic surfaces. In the ranging mode, centimeter-level precise baseline and station coordinate determinations will be made on grids consisting of 100 to 200 targets separated by distances from a few tens of kilometers to about 1000 km. These measurements will be used for studies of seismic zone crustal deformations and tectonic plate motions. Ranging measurements will also be made to a coarser, but globally distributed array of retroreflectors for both precise geodetic and orbit determination applications. In the altimetric mode, relative height determinations will be obtained with approximately decimeter vertical precision and 70 to 100 meter horizontal resolution. The height data will be used to study surface topography and roughness, ice sheet and lava flow thickness, and ocean dynamics. Waveform digitization will provide a measure of the vertical extent of topography within each footprint. The planned Earth Observing System is an attractive candidate platform for GLARS since the GLAR data can be used both for direct analyses and for highly precise orbit determination needed in the reduction of data from other sensors on the multi-instrument platform. (1064, 532, and 355 nm)Nd:YAG laser meets the performance specifications for the system.

Cohen, S. C.↗

NASA NTRS1985

A perspective on the evidence for periodic cometary impacts on earth

Recent suggestions of periodic cometary showers coincident with mass extinctions have prompted a review of the terrestrial cratering record. From the point of view of completeness of search and crater retention, the record used to argue for statistical periodicities is incomplete and may not be representative. Estimates of crater ages are of variable accuracy and precision and, in some cases, different dating methods yield discordant results. It is possible to define through time-series analysis a number of periodicities of different magnitude (about 29, 21, 18.5, and 13.5 m.y.) and phase, depending on which craters are considered the most representative sample of the record. Arguing against periodic cometary showers is the observation that estimates of the average cratering rate in recent time and observations on Apollo bodies are equivalent. In addition, siderophile element data from impact melt rocks suggest a variety of projectile types were responsible for relatively large terrestrial craters. Given these observations, it is concluded that statements regarding periodic cometray showers are not categorical and require evidence beyond arguments based on time-series analyses of an incomplete cratering record.

Grieve, R. A. F.↗

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

Characteristics of Basaltic Lava Flows on Venus

Some ideas relating to the formation of lava flows on Venus are reviewed. The surface morphological features seen in the panoramic images made by the Venera 13 and 14 landers are examined in detail. The major element compositions measured by the Soviet probes indicate that the surface rocks at the Venera 13 site resemble a terrestrial tholeite composite whereas the Venera 14 rocks are similar to terrestrial alkali basalts. Few data exist on the rheological properties of such magma types on Earth; these properties are a strong function of magma volatile content, and there are important gaps in our knowledge of the typical volatiles to be associated with the magmas on Venus. However, the suggestion that Venusian magmas may be water poor together with consideration of the fact that the high Venusian surface temperatures may cause magmas to experience up to 50 K less cooling during their rise to the surface than corresponding terrestrial counterparts, leads to the finding that Venusian magmas may typically have plastic viscosities, E, up to a factor of three greater than terrestrial counterparts on eruption. A similar analysis of yield strength variations with temperature, magma composition and volatile content suggests that temperature will exert the main control and that Venusian magma yield strengths, Y, may be a factor of several times smaller than those of terrestrial equivalents.

Wilson, L.↗

NASA NTRS1985

Surface Units on Venus Derived from Pioneer-venus Altimetry, Roughness, and Reflectivity Measurements

The nature of the Venusian surface was revealed by Pioneer-Venus (PV) observations to be diverse at scales from tens to hundreds of kilometers. Spatial correlations of elevation, surface roughness, and radar reflectivity were investigated as a means of assessing the degree of homogeneity of surface radar properties within topographic provinces and develop a map of possible geologic boundaries. Correlations were performed in a supervised fashion whereby unit boundaries were selected on the basis of statistical and empirical studies of the individual data sets. Interpretations of these units in terms of geologic characteristics are based on the determination of physical units which are model dependent.

Peterfreund, A. R.↗

NASA NTRS1985

Periodic cometary showers: Real or imaginary?

Since the initial reports in 1980, a considerable body of chemical and physical evidence has been accumulated to indicate that a major impact event occurred on earth 65 million years ago. The effects of this event were global in extent and have been suggested as the cause of the sudden demise or mass extinction of a large percentage of life, including the dinosaurs, at the end of the geologic time period known as the Cretaceous. Recent statistical analyses of extinctions in the marine faunal record for the last 250 million years have suggested that mass extinctions may occur with a periodicity of every 26 to 30 million years. Following these results, other workers have attempted to demonstrate that these extinction events, like that at the end of the Cretaceous, are temporally correlated with large impact events. A recent scenario suggests that they are the result of periodic showers of comets produced by either the passage of the solar system through the galactic plane or by perturbations of the cometary cloud in the outer solar system by a, as yet unseen, solar companion. This hypothesized solar companion has been given the name Nemesis.

Grieve, R. A. F.↗

NASA NTRS1984

A geometric model for excavation and modification at terrestrial simple impact craters

A geometric model for the excavation and modification stages of simple crater development is presented. Cavity modification is modelled from an analytical derivation of the dimensions of the so-called transient cavity (Dence, 1973; Dence et al., 1977). The final cavity as it appears in terrestrial craters and the primary elements of excavation are approximated by a variation of the so-called Z model. The applicability of the model is tested with data from the Meteor and Brent craters. In the case of Meteor, the modelled final crater diameter at the original ground plane is within 26 m of the observed value and the modelled breccia lens and the rim crest volumes of the final true crater are within 9.5 percent and 2.5 percent, respectively, of the observed values. The correspondence for the more degraded Brent crater is less precise.

Grieve, R. A. F.↗

NASA NTRS1984

Venus - The nature of the surface from Venera panoramas

The present investigation has the objective to analyze the information collected by the Soviet Venera 9, 10, 13, and 14 lander spacecraft imaging systems. The analysis is to make a systematic comparison with other planetary surfaces possible, and an improved understanding of the surface of the planet Venus is to be provided. Attention is given to the imaging systems and transformation methods, observations, the observed characteristics of Venera lander sites, and an interpretation of the geological processes responsible for the features observed in the Venera panoramas. It is concluded that the present Venus environment is considerably different in terms of temperature, pressure, and atmosphere composition from the present terrestrial subaerial environment.

Garvin, J. B.↗

NASA NTRS1984

Venus: The nature of the surface from Venera panoramas

Images of the surface of Venus obtained by the Soviet Venera 9, 10, 13 and 14 landers are analyzed to provide a basis for understanding the nature of geologic processes operating there. Bedrock is exposed at the Venera 10, 13 and 14 sites and is characterized by semi-continuous, flat polygonal to subrounded patches up to several meters in width. The bedrock surface is often dominated by sub horizontal to horizontal layered plates with thicknesses of several cm and abundant linear and polygonal vertical fractures. Soils (particles 1 cm) are abundant at the Venera 9, 10 and 13 sites, but are uncommon at Venera 14. Features indicative of a strong aeolian influence (moats, dunes, wind tails) are not observed. Several hypotheses are considered for the origin of the bedrock surfaces, and it is concluded that bedrock originated from surface lava flows. The relative freshness of features observed by the Veneras suggests that erosion rates are very low or that some bedrock surfaces are geologically young.

Garvin, J. B.↗