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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Volcanism and Rift Formation in Beta Regio, Venus: New Radar Results

A high resolution (approximately 2 km) image of Beta Regio, Venus, obtained with the Arecibo radar system, reveals additional details of structure which seem to confirm past suggestions that this region consists of a rift system and associated volcanism. Numerous long linear features approximately parallel to the north-south trending trough discovered by the Pioneer-Venus Orbiter are interpreted as being indicative of extensive faulting and the detail for the radar reflectivity anomaly coincident with Theia Mons suggests that it is a major volcano situated on what would be the western bounding fault of the rift system.

Campbell, D. B.↗
NASA NTRS1985

Transformation of Polar Ice Sublimate Residue into Martian Circumpolar Sand

The experimental demonstration that a credible Martian sand may be formed from dust-bearing ice provides a new set of possible explanations for some of the observed Martian aeolian landforms. It is hypothesized that a light-weight fluffy rind is formed on the polar caps. This could provide material easily entrainable by Martian winds, which generally blow equatorward from the poles. These winds would peel the fluffy rind from the surface of the sublimating summer polar caps and from the equatorward slopes of the polar troughs. These pieces of material would then be rolled into lumps (of high sailarea/mass ratio) by the wind. They would become pigmented as they saltate across the surface, perhaps gathering carbonaceous meteoritic dust or other impurities on their surfaces, or through chemical reactions with the ice-free environment away from their point of origin. Once they became trapped in topographic wind shadows, they would form dune structures because they are hydraulically equivalent to sand particles.

Saunders, R. S.↗
NASA NTRS1985

Terrestrial Analog Studies for Martian Patterned Ground

A recurring problem in understanding Martian patterned ground is explaining its large size. Terrestrial patterned ground in Swedish Lapland offers an analog that may help explain this. In cold, arid regions with strong winds, polygonal features are accentuated paralled to the dominant wind direction. Preliminary results of a comparison between Martian polygonal troughs and dominant wind directions suggests a good correlation. This evolutionary model involving aeolian modification of Martian polygonal ground helps explain the large size features without requiring multiple, deep freeze-thaw cycles. A well-established geographical technique, nearest neighbor analysis, can be modified and applied to the distribution of patterned ground on Earth and Mars. The procedure determines the R-statistic, which reflects the degree to which on observation departs from an expected random pattern. The R-statistic is independent of scale, and therefore it can be applied to any size of type of pattern. Preliminary results indicate that there may be a correlation between the R-statistic and the process that create the polygons.

Rossbacher, L. A.↗
NASA NTRS1985

The Geomorphology of Rhea

Rhea was imaged to a resolution of approximately 1 km/lp by the Voyager spacecraft, providing the most detailed view of any Saturnian satellite. A preliminary study of Rhea divided the northern hemisphere into population 1 cratered terrain (between 20 deg and 120 deg) and population 2 cratered terrain (between 300 deg and 360 deg). Population 1 includes craters that are 40 km and were formed before the termination of population 2 bombardment, which formed craters primarily 40 km. Several geomorphic features on Rhea are classified and interpreted including three physiographic provinces, multiringed basins, craters, megascarps, ridges and scarps, and troughs and coalescing pit chains. A generalized chronology for Rhea is constructed from an analysis of the superposition relationships among the landforms and physiographic provinces.

Moore, J. M.↗
NASA NTRS1985

Valles Marineris Basin Beds: a Complex Story

High resolution stereoimages of the central Valles Marineris enabled detailed geologic mapping on Ophir and Candor Chasmata. Abundant light colored deposits, both layered and massive, fill the chasmata in this region. Units within these deposits were identified by their erosional characteristics and superposition and cross cutting relations. The Valles Marineris beds reflect a history of repeated faulting, volcanic eruptions, and deposition and erosion, resulting in stratigraphic sequences with several unconformities. Because of the preponderance of apparent volcanic deposits inside the troughs, the chasmata may not be simple grabens, but rather giant volcano tectonic depressions. Major events in chasmata development are examined.

Lucchitta, B. K.↗
NASA NTRS1985

Multistage spent particle collector and a method for making same

A description is given of a spent particle collector which maintains structural integrity when raised to a high temperature although constructed of materials having widely different coefficients of expansion. The collector is comprised of one or more axisymmetric stages, each stage comprising a subassembly. A subassembly includes an inner pyrolytic graphite ring, a transition ring, a ceramic insulator ring and an outer metal ring which forms part of the wall of the collector. Each transition is of a ductile metal having high thermal conductivity and is provided with an annular sputter shield wall extending toward the source of spent particles and, where necessary, a trough in the other surface to enclose the sputter shield of the next adjacent transition ring. A plurality of radial extending slots are provided in a transition ring to form segments which are retained in their position by the sputter shield.

Ebihara, B. T.↗
NASA NTRS1983

Cold plasma distribution above a few thousand kilometers at high latitudes

Great advances with respect to the study of the earth's magnetosphere could be achieved in connection with the launch of the Dynamics Explorer (DE) 1 and 2 spacecraft. These advances were made possible partly because of the unique combination of coplanar orbits which simultaneously sample the low altitude ionospheric and atmospheric signature (DE-2) and the high altitude phenomena of the inner magnetosphere (DE-1). It was, thus, feasible to obtain new measurements of the coupling of plasmas and fields between these fundamentally important regions. One basic element of the coupling involves the interchange of low energy plasma between the ionosphere and magnetosphere. The flow characteristics of the low energy plasma are indicators of the magnetospheric and ionospheric electric fields which drive the current system. The Retarding Ion Mass Spectrometer (RIMS) instrument has been designed for conducting measurements regarding this plasma population. Attention is given to details regarding RIMS, an example RIMS orbit, plasma trough characteristics, and polar cap phenomena.

Chappell, C. R.↗
NASA NTRS1984

Concentrations and isotope ratios of carbon, nitrogen and sulfur in ocean-floor basalts

Ocean floor basalts studied from the Galapagos Ridge, FAMOUS area, Cayman Trough and Kilauea east rift contain 20-200 ppm carbon and 0.3-2.8 ppn nitrogen as sums of the vesicle-filling gases CO2 and N2 and dissolved species. The wide range of carbon contents found is due partly to the different extent of outgassing of vesicle-filling gases and partly to depth dependency of dissolved CO2 in the basalts. Sulfate commonly exists with sulfide in these basalts, and the sulfate/sulfide ratio increases with increasing water content, perhaps reflecting the higher oxidation potential in basalt melt of the higher water content.

Sakai, H.↗
NASA NTRS1983

Determination of atmospheric properties from lidar measurements

Differential absorption lidar techniques for determining basic atmospheric properties to high accuracy are described. The theory of a two-wavelength lidar temperature measurement is given with simulation results that show accuracies of 0.5 to 1 K for measurements from ground-based and satellite platforms. The theory of measurements of the atmospheric pressure profile using absorption troughs, broad regions of nearly uniform absorption, is also described with simulation results that show accuracies of 0.1 to 0.3 percent. Recent measurements which confirm the accuracy of these techniques are reviewed.

Korb, C. L.↗
NASA NTRS1985

Emission-line QSOs in the region of the Hercules cluster of galaxies

Slit spectrophotometry in the 305-855-nm range of 25 QSO candidates identified by slitless spectroscopy in two 1-deg-sq fields (one centered on Abell 2151 and one in a blank region) near the Hercules cluster of galaxies, obtained using image-dissector scanners on the 3-m Lick Observatory and 4-m KPNO telescopes at resolution 5-20 A during 1976-1979, are reported. The data are presented in tables and spectrograms and characterized in detail. In the cluster field, 14 candidates are confirmed as QSOs with z = 0.89-3.24; in the blank field, six are confirmed with z = 1.52-3.00. While the strongest feature of most spectra is found to be the Lyman alpha line, five QSOs have the 154.9-nm line of C IV and one the semiforbidden 190.9-nm line of C III as strong features. The wide variety of spectral profiles and absorption features in the higher-redshift QSOs and the lack of any QSOs with broad absorption troughs are discussed, and the use of these QSOs as probes for warm or cool gas in the Hercules cluster in Space Telescope Faint Object Spectrograph observations is suggested.

Burbidge, E. M.↗
NASA NTRS1985

Thermal ion temperatures from the retarding ion mass spectrometer on DE 1

Data from the retarding ion mass spectrometer (RIMS) on Dynamics Explorer 1 are analyzed by means of a thin sheath model to determine ion temperatures. A number of characteristic features of ion temperatures in and near the plasmasphere are presented. Typical H(+) temperatures in the plasmasphere are found to be 4000 K to 6000 K on the morningside and 2000 K to 4000 K on the eveningside, increasing with L throughout. In the plasma trough, typical temperatures observed are a few times 10,000 K. In the outer plasmasphere, multiple temperature components are frequently observed. H(+) and He(+) ions are found to be very close to thermal equilibrium with each other in all but perhaps the outer part of the plasmasphere. Within the plasmasphere, temperature profiles observed by DE 1/RIMS rarely show small-scale variation. During geomagnetically active times, high-altitude temperatures between L = 2 and 3 appear to be depressed over quiet time values, to the extent that they may be cooler than temperatures at low altitudes along approximately the same field line.

Comfort, R. H.↗
NASA NTRS1984

Ionospheric variations affecting altimeter measurements - A brief synopsis

Data on quiet-time ionospheric fluctuations on scales from 1 km to thousands of kilometers are reviewed. The effect of the fluctuations on satellite altimeter measurements are discussed, and corrections for both small scale and large-scale fluctuations are given. Large scale changes are considered to be those on scales greater than 500 km or 1 hr. Temporal changes were found to occur on solar, seasonal, and diurnal scales. Spatial variations include the equatorial anomaly and the mid-latitude trough. The correlation distance of the ionosphere (70 percent correlation) was approximately 2500-3000 km east-west and 1600 km north-south. It is shown that small scale flutuations can be described by a power law spectrum with a one-dimensional index of -1.5 to -2.0. The observed spectrum of density flutucations gave a vertical line-of-sight path-length fluctuation of 1-40 mm, on a horizontal scale of 1-500 km, for a radio signal at 13.7 GHz.

Callahan, P. S.↗
NASA NTRS1984

Electromagnetic bias of 10-GHz radar altimeter measurements of MSL

Electromagnetic bias, the small difference that exists between the radar measured mean sea level and the geometric mean sea level is an important issue in high precision satellite altimetry. Present day satellite altimetry has achieved, with SEASAT-1, a precision of 5 cm rms in the range measurement. Future altimeter designs are expected to improve the range measurement precision to cm rms. In order to exploit the capability of these precise radar altimeters are marine geodesy and oceanography, it is necessary to understand and account for all of the known biases in the range measurement. The electromagnetic bias or the EM bias, which has been attributed to the observed fact that ocean wave troughs tend to be better reflectors of nadir viewing microwave radar energy than ocean wave crests, can be observed with high resolution airborne radar. This report presents the results of the EM bias measurements made by NRL using an airborne radar altimeter operating at 10 GHz with a 1 ns range resolution. Data were taken for various sea states and wind conditions. The experimental results are compared with current theories.

Choy, L. W.↗
NASA NTRS1984

The reflection of airborne UV laser pulses from the ocean

It is experimentally shown here for the first time that the normalized laser backscatter cross-section of the sea surface is a function of elevation or height position on teh ocean wave. All data were taken off-nadir, resulting in incidence angles of about 6.5 deg measured relative to the normal to mean sea level (MSL). In the limited data sets analyzed to date, the normalized backscatter cross-section was found to be higher in wave crest regions and lower in wave troughs for a swell-dominated sea over which the wind speed was 5 m/s. The reverse was found to be the case for a sea that was driven by a 14 m/s wind. These isolated results show that the MSL, as measured by an off-nadir and/or multibeam type satellite laser altimeter, will be found above, at, or below the true MSL, depending on the local sea conditions existing in the footprint of the altimeter. Airborne nadir-pointed laser altimeter data for a wide variety of sea conditions are needed before a final determination can be made of the effect of sea state on the backscatter cross-section as measured by a down-looking satellite laser system.

Hoge, F. E.↗
NASA NTRS1984

Cenozoic rift formation in the northern Caribbean

Rifts form in many different tectonic environments where the lithosphere is put into extension. An outline is provided of the distribution, orientation, and relative ages of 16 Cenozoic rifts along the northern edge of the Caribbean plate and it is suggested that these structures formed successively by localized extension as the Caribbean plate moved eastward past a continental promontory of North America. Evidence leading to this conclusion includes (1) recognition that the rifts become progressively younger westward; (2) a two-phase subsidence history in a rift exposed by upthrusting in Jamaica; (3) the absence of rifts east of Jamaica; and (4) the observation that removal of 1400 km of strike-slip displacement on the Cayman Trough fault system places the Paleogene rifts of Jamaica in an active area of extension south of Yucatan where the rifts of Honduras and Guatemala are forming today.

Mann, P.↗
NASA NTRS1985

Development of a boundary-layer-type solver based on simultaneous iteration technique for axisymmetric separated flows

A boundary-layer-type solver is developed for the numerical solution of axisymmetric separated flows. A new fully implicit coupling scheme for the viscous and inviscid regions is demonstrated. This fully implicit coupling technique is similar to the work of Carter, Veldman, and an extension of an earlier work of Halim and Hafez. A comparison is made for the convergence rate using this new fully implicit coupling technique and the semiimplicit coupling of Halim and Hafez. Numerical results using the fully implicit coupling are obtained for laminar incompressible separated flows, including a boattail and a series of trough geometries. Also, the near-wake flow problem is considered using the present formulation. A clear conclusion of this investigation is that the present scheme using the fully implicit coupling method converges at a faster rate than the semiimplicit coupling and the partially parabolized Navier-Stokes (PPNS) procedures.

Halim, A. A. M.↗
NASA NTRS1985

The source of midlatitude metallic ions at F-region altitudes

The results of a survey of metallic ions detected by the Bennett Ion Mass Spectrometer flown on the Atmospheric Explorer satellites are presented and discussed. The nighttime distribution of these ions observed in the F-region at middle latitudes can be accounted for by the presence of fast upward Pederson ion drifts that are produced by intense poleward-directed electric fields with magnitudes typical of those defining subauroral drift events. Such fields, which arise in the vicinity of the main electron density trough at night, result in the rapid movement of long-lived meteoric ions upwards out of their source region into the F-region. Neutral wind drag by the equatorially-directed nightside neutral wind component can lift the ions higher along the field lines until the downward drag of major ion diffusion forces them to layer under F-max.

Grebowsky, J. M.↗
NASA NTRS1985

Small-scale convection beneath the transverse ranges, California: Implications for interpretation of gravity anomalies

Tomographic inversion of upper mantle P wave velocity heterogeneities beneath southern California shows two prominent features: an east-west trending curtain of high velocity material (up to 3% fast) in the upper 250 km beneath the Transverse Ranges and a region of low velocity material (up to 4% slow) in the 100 km beneath the Salton Trough. These seismic velocity anomalies were interpreted as due to small scale convection in the mantle. Using this hypothesis and assuming that temperature and density anomalies are linearly related to seismic velocity anomalies through standard coefficients of proportionality, leads to inferred variations of approx. + or - 300 C and approx. + or - 0.03 g/cc.

Humphreys, E. D.↗