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At least 325 records · Page 18

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NASA NTRS1981

Optical polarimetry of Comet West 1976 VI

Four narrowband filters covering the 440-850 nm wavelengths were used to measure the polarization of the continuum of Comet West 1976 VI. Postperihelion observations indicated wavelength-independent linear polarization in all of the three measurements made, in agreement with other polarization measurements of the comet from the visible to the near-infrared but in contrast with the general tendency in comets toward polarization increase with wavelength. No circular polarization was detected, and it is suggested by (1) the magnitude of polarization as a function of scattering angle, (2) wavelength independence, and (3) infrared and optical photometric properties, that dirty silicates with radii approaching 5 microns may be responsible for the phenomena observed.

Michalsky, J. J.↗

NASA NTRS1982

Aircraft measurement of sea surface temperature during the West Coast Experiment

During the West Coast Experiment in March 1977, a test was conducted to ascertain the effectiveness of using remote sensing techniques to estimate sea surface temperature (SST) from infrared (IR) emissions of the sea surface. Aircraft flights were made over three buoys moored in southern California coastal waters, and data was collected of sea surface emissions at thermal IR wavelengths (7.95-13.5 micrometers). SST obtained from the remote sensing measurements were compared with in situ SST measured with thermistors mounted on the buoys. The remotely determined SST were from 1.4-2.9 C lower than the in situ measurements. Several factors are discussed that could account for the differences.

Schieldge, J. P.↗

NASA NTRS1981

Remote sensing in West Virginia

Low altitude black and white aerial photography is the prinicipal remote sensing tool for geologic investigations in West Virginia, although side looking radar and color infrared photography are also used. The first land use/cover map for the state was produced in color infrared and is being digitized. Linear features in Cabell and Wayne Counties, as revealed by LANDSAT, were evaluated to test the possible correlations with rock fractures and gas production from shales. A LANDSAT linear features map (1:250,000) was prepared for the entire state, also. Presently investigations are being made to understand karst and to predict areas that should not be used for development. Aerial photography and field mapping is being conducted to detect the location and causes of landslides.

Lessing, P.↗

NASA NTRS1983

MIZEX-WEST NASA CV-990 flight report

As part of the Bering Sea marginal ice zone winter experiment (MIZEX-WEST), the CV-990 airborne laboratory was flown to assess the potential of using an extended range of wavelengths for improving passive microwave sea ice observations from spacecraft and second to provide an overview of the MIZ for large-scale processes studies. The aircraft was equipped with both imaging and fixed-beam, dual-polarized passive microwave radiometers ranging from 1.5 millimeter to 3 centimeter wavelengths. Visual, photographic, and thermal (10.7 micron) infrared surface observations were also made from the aircraft to complement the microwave measurements. The flight operations and in-flight observations are discussed and each flight is summarized including flight objective and instrument status. Preliminary mosaic images obtained with the ESMR imager, Nimbus-7 orbits over the Bering Sea, ice observations obtained by an ice observer on board, and composite maps of the general ice conditions for the month of February are also presented.

Cavalieri, D. J.↗

NASA NTRS1983

An investigation of MAGSAT and complementary data emphasizing precambrian shields and adjacent areas of West Africa and South America

There is lack of acceptance of quantitative crustal models by specialists on regional geology because of the problem of east-west banding on MAGSAT anomaly maps. The possibility of some of the Earth's magnetic field being created in the mantle below the Curie isotherm is discussed as well as the need to remove spherical harmonics of degrees less than 15 from the anomaly map. Two dimensional models were produced for northern South America that might be considered as working models. These models suggest that the presumed Amazon River depression is better developed near Belem and in the upper Amazon basin than in the central Amazon basin. An attempt is proposed for separating the core field from the crustal field using a flat-Earth model.

Hastings, D. A.↗

NASA NTRS1982

Factors in the Effective Utilization of a LANDSAT Related Inventory in West Africa

A comprehensive LANDSAT related resource inventory was performed in parts of Ghana, Benin, and Upper Volta to determine resource development potential in areas freed of the disease onchocerciasis. The ultimate success of the project lies in the effective use of the data by host country personnel in resource development projects. This requires project follow-through, adequate training of regional counterparts, and integration of the data into an easily used framework. Present levels of support systems and technical expertise in West Africa indicate that an automated system for natural resource data is not currently appropriate. Suggestions for the greater implementation of such inventories are explored.

Hall, L.↗

NASA NTRS1983

The 0.9-2.5 micron spectrum of Comet West 1976 VI

Analyses of IR data of Comet West in the region 0.9-2.5 microns are presented. The spectra were observed with a resolution of 4.6/cm, and the solar-type star Eta Boo was also observed for comparison purposes. The cometary continuum was found to increase slightly from 10,000-5500/cm, and display thermal emission above 5500/cm due to dust particles in the coma. The cometary emissions were identified with CN and C2, with the C2 transitions displaying unblended singlet and triplet systems. It is noted that no emissions or absorptions due to ice of any form were detected.

Johnson, J. R.↗

NASA NTRS1983

Average sedimentary rock rare Earth element patterns and crustal evolution: Some observations and implications from the 3800 Ma ISUA supracrustal belt, West Greenland

Rare earth element (REE) data is given on a set of clastic metasediments from the 3800 Ma Isua Supracrustal belt, West Greenland. Each of two units from the same sedimentary sequence has a distinctive REE pattern, but the average of these rocks bears a very strong resemblance to the REE pattern for the North American Shale Composite (NASC), and departs considerably from previous estimates of REE patterns in Archaean sediments. The possibility that the source area for the Isua sediments resembled that of the NASC is regarded as highly unlikely. However, REE patterns like that in the NASC may be produced by sedimentary recycling of material yielding patterns such as are found at Isua. The results lead to the following tentative conclusions: (1) The REE patterns for Isua Seq. B MBG indicate the existence of crustal materials with fractionated REE and negative Eu anomalies at 3800 Ma, (2) The average Seq. B REE pattern resembles that of the North American Shale Composite (NASC), (3) If the Seq. B average is truly representative of its crustal sources, then this early crust could have been extensively differentiated. In this regard, a proper understanding of the NASC pattern, and its relationship to post-Archaean crustal REE reservoirs, is essential, (4) The Isua results may represent a local effect.

Dymek, R. F.↗

NASA NTRS1984

Final Comparison of TM and MSS Data for Surface Mine Assessment in Logan County, West Virginia

A variety of classifications during both raw and transformed MSS and TM data sets from 4 September 1982 were performed for the Logan County, West Virginia study area. The object was to compare the utility of TM and MSS data for delineating small, irregular ground features, particularly surface mines, and also to test data reduction/transformation techniques (band selection, canonical analysis, and principal components) in relation to a traditional means of unsupervised classification. Statistical results demonstrate that, on the average, the TM classifications yielded an overall .53 factor of improvement relative to the MSS classifications. When the accuracies for only three minor (in terms of areal extent) land use categories are examined, the factor of improvement for TM over MSS increases to 1.48; i.e., the TM is nearly one and one-half times better than the MSS for delineating small and irregular ground features such as contour strip mines.

Witt, R. G.↗

NASA NTRS1983

Performance of an airborne imaging 92/183 GHz radiometer during the Bering Sea Marginal Ice Zone Experiment (MIZEX-WEST)

An airborne imaging 92/183 GHz radiometer was recently flown onboard NASA's Convair 990 research aircraft during the February 1983 Bering Sea Marginal Ice Zone Experiment (MIZEX-WEST). The 92 GHz portion of the radiometer was used to gather ice signature data and to generate real-time millimeter wave images of the marginal ice zone. Dry atmospheric conditions in the Arctic resulted in good surface ice signature data for the 183 GHz double sideband (DSB) channel situated + or - 8.75 GHz away from the water vapor absorption line. The radiometer's beam scanner imaged the marginal ice zone over a + or - 45 degrees swath angle about the aircraft nadir position. The aircraft altitude was 30,000 feet (9.20 km) maximum and 3,000 feet (0.92 km) minimum during the various data runs. Calculations of the minimum detectable target (ice) size for the radiometer as a function of aircraft altitude were performed. In addition, the change in the atmospheric attenuation at 92 GHz under varying weather conditions was incorporated into the target size calculations. A radiometric image of surface ice at 92 GHz in the marginal ice zone is included.

Gagliano, J. A.↗

NASA NTRS1984

Geochemical constraints on magma processes in a peralkaline system - The Paisano volcano, west Texas

Petrographic and trace element data from a continuous stratigraphic sequence of flows from the peralkaline Paisano Volcano in west Texas are used to delineate magnetic processes responsible for the chemical evolution of this volcano. It is shown that crystal fractionation of the phenocrystic assemblage explains the main compositional variation, but magma mixing of a less evolved melt composition also affected the chemical evolution of the volcano.

Mcdonough, W. F.↗

NASA NTRS1985

Venus gravity west of Beta Regio

Doppler tracking data from the Pioneer Venus Orbiter (PVO) have been used to estimate the anomalous gravity field in the region of Venus west of Beta Regio. The analysis invokes a Kalman filter-smoother to solve the nonlinear spacecraft state estimation problem and a linear Bayesian estimator to perform the geophysical inversion. The topographic map for this region, derived from the PVO radar, has been filtered to have the same distortions and degree of smoothing as the gravity map. The undulations of the gravity are about 0.2 times as large as expected from the topography, on the assumption that the latter is uncompensated. A comparison of the gravity and topography by means of the spectral admittance is consistent with Airy compensation at a depth of 50 km, if the surface material has a density of 2.6 g/cu cm. However, this is not a unique interpretation.

Goldberg, Z. M.↗

NASA NTRS1985

Does the geoid drift west?

In 1970 Hide and Malin noted a correlation of about 0.8 between the geoid and the geomagnetic potential at the Earth's surface when the latter is rotated eastward in longitude by about 160 degrees and the spherical harmonic expansions of both functions are truncated at degree 4. From a century of magnetic observatory data, Hide and Malin inferred an average magnetic westward drift rate of about 0.27 degrees/year. They attributed the magnetic-gravitational correlation to a core event at about 1350 A.D. which impressed the mantle's gravity pattern at long wavelengths onto the core motion and the resulting magnetic field. The impressed pattern was then carried westward 160 degrees by the nsuing magnetic westward drift. An alternative possibility is some sort of steady physical coupling between the magnetic and gravitational fields (perhaps migration of Hide's bumps on the core-mantle interface). This model predicts that the geoid will drift west at the magnetic rate. On a rigid earth, the resulting changes in sea level would be easily observed, but they could be masked by adjustment of the mantle if it has a shell with viscosity considerably less than 10 to the 21 poise. However, steady westward drift of the geoid also predicts secular changes in g, the local acceleration of gravity, at land stations. These changes are now ruled out by recent independent high-accuracy absolute measurements of g made by several workers at various locations in the Northern Hemisphere.

Backus, G. E.↗

NASA NTRS1986

Strontium and neodymium isotopic variations in early Archean gneisses affected by middle to late Archean high-grade metamorphic processes: West Greenland and Labrador

Relicts of continental crust formed more than 3400 Ma ago are preserved fortuitously in most cratons. The cratons provide the most direct information about crust and mantle evolutionary processes during the first billion years of Earth history. In view of their polymetamorphic character, these terrains are commonly affected by subsequent tectonothermal events. Hence, their isotope systematics may be severely disturbed as a result of bulk chemical change or local isotopic homogenization. This leads to equivocal age and source information for different components within these terrains. The Sr and Nd isotopic data are presented for early Archean gneisses from the North Atlantic Craton in west Greenland and northern Labrador which were affected by younger metamorphic events.

Collerson, K. D.↗

NASA NTRS1986

The Archean geology of the Godthabsfjord Region, southern west Greenland (includes excursion guide)

The part of the West Greenland Archean gneiss complex centered around Godthabsfjord and extending from Isukasia in the north to south Faeringehavn is studied. Extensive outcrops of 3800 to 3400 Ma rocks can provide some direct evidence of conditions and processes that operated on the Earth in the early Archean. However, the ways in which primary characteristics have been modified by later deformation, metamorphism, and chemical changes are first taken into account. The rocks exposed are the products of two major phases of accretion of continental crust, at 3800 to 3700 Ma and 3100 to 29 Ma. The main features of these two accretion phases are similar, but careful study of the least modified rocks may reveal differences related to changes in the Earth in the intervening period. The combination of excellent exposure over an extensive area, relatively detailed geological mapping of much of the region, and a considerable volume of isotopic and other geochemical data gives special insights into processes that operated at moderately deep levels of the crust in the Archean. Of particular interest is the effect of late Archean granulite facies metamorphism on early Archean rocks, especially the extent to which isotope systems were disturbed. Similar processes may well have partly or wholly destroyed evidence of more ancient components of other high grade terrains. This account does not attempt to be an exhaustive review of all work carried out on the geology of the region. Rather, it attempts to summarize aspects of the geology and some interest in the context of early crustal genesis.

Mcgregor, V. R.↗

NASA NTRS1986

A remanent and induced magnetization model of Magsat vector anomalies over the west African craton

Scalar and vector Magsat anomalies over the west African craton are analyzed by forward and inverse models. A forward model of the Man shield is based on Liberia. Induced magnetization contrasts due to sporadic iron-formations and to regional metamorphic rocks, and a contrast in remanent magnetization within the lower crust are included. This combination reproduces the location, magnitude and adopted local zero level of anomalies in the initial Magsat maps. An inverse model of the Reguibat shield estimates the magnetization contrast of its lithosphere, and when magnetism is restricted to shallower than 75 km both shields can be represented by a susceptibility contrast of +0.02. A residual anomaly between the shields involves a relative deficiency of induced magnetization along with other causes.

Toft, P. B.↗

NASA NTRS1987

Geomorphic evidence for ancient seas in west Deuteronilus Mensae, Mars-1: Regional geomorphology

The fretted terrain in west Deuteronilus Mensae consists of extensive cratered upland penninsulas or isolated plateaus cut by long, finger-like canyons typically 10 to 20 km wide and upwards of 300 km long. The longest of these canyons trend roughly north-south to north-northeast, which may reflect some local structural and/or topographic control. At least three geomorphic zones roughly parallel to the lowland/upland boundary, suggestive of increasing modification northward, can be recognized on the fretted region of the region. The southern-most zone (zone A) consists of sharply defined fretted terrain. The middle zone (zone B) consists of well defined fretted terrain in which the plateau surfaces appear smoother, with a somewhat darker and much less varied albedo surface than those of zone A. The northern-most zone (zone C) consists of rounded or softened fretted terrain. The zones were interpreted as surface exposures of successively lower stratigraphic units.

Parker, Timothy J.↗

NASA NTRS1987

Cosmic-ray positrons from 10 to 20 GeV - A balloon-borne measurement using the geomagnetic east-west asymmetry

Results are reported for cosmic-ray positrons obtained in a balloon flight of the University of Chicago electron telescope in Hawaii in April 1984. Making use of the east-west asymmetry in the geomagnetic cutoff rigidity, cosmic-ray positrons and negatrons were separated over the range 10-20 GeV. The resulting positron to electron ratio is 12-22 percent, significantly higher than the ratio measured in the 1-10 Gev range by other experiments. This increase appears to suggest that either a primary component of positrons becomes significant above 10 GeV or that the spectrum of primary negatrons decreases above 10 GeV more sharply than that of secondary positrons.

Mueller, Dietrich↗