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At least 379 records · Page 21

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NASA NTRS1985

Late-Quaternary climatic change on the American North Pacific Coast

The late Quaternary climate of the North Pacific, where according to modelling the solar radiation in the early Holocene at the time of the summer solstice is high and in the late Holocene is relatively low, is investigated. Quantitative temperature and precipitation estimates from southern Alaska are compared with estimates from western Washington and British Columbia. Data extending over more than 10,000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the North Pacific Ocean. In the early Holocene, the subtropical North Pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present, so that warmth and dryness increased in southern Alaska. The Aleutian low-pressure center intensified during the late Holocene, resulting in colder and more humid coastal climate and increased frequency of glacier growth in the cordillera.

Heusser, C. J.↗

NASA NTRS1986

Thematic mapper studies of Andean volcanoes

The primary objective was to identify all the active volcanoes in the Andean region of Bolivia. Morphological features of the Tata Sabaya volcano, Bolivia, were studied with the thematic mapper. Details include marginal levees on lava and pyroclastic flows, and summit crater structure. Valley glacier moraine deposits, not easily identified on the multispectral band scanner, were also unambiguous, and provide useful marker horizons on large volcanic edifices which were built up in preglacial times but which were active subsequently. With such high resolution imagery, it is not only possible to identify potentially active volcanoes, but also to use standard photogeological interpretation to outline the history of individual volcanoes.

Francis, P. W.↗

NASA NTRS1986

Entrainment, transport and concentration of meteorites in polar ice sheets

Glaciers and ice sheets act as slow-moving conveyancing systems for material added to both their upper and lower surfaces. Because the transit time for most materials is extremely long the ice acts as a major global storage facility. The effects of horizontal and vertical motions on the flow patterns of Antarctic ice sheets are summarized. The determination of the source areas of meteorites and their transport paths is a problem of central importance since it relates not only directly to concentration mechanisms but also to the wider issues in glaciology and meteorites. The ice and snow into which a meteorite falls, and which moves with it to the concentration area, encodes information about the infall area. The principle environmental conditions being former elevation, temperature (also related to elevation), and age of the ice. This encoded information could be used to identify the infall area.

Drewry, D. J.↗

NASA NTRS1986

Radioactivities in returned lunar materials and in meteorites

A preliminary C-14 study on lunar soil was carried out with the University of Toronto Iso Trace accelerator mass spectrometer. This accelerator was recommended for C-14 work by Dr. R. Schneider of A.S. and E., who was the field engineer during the assemblage and start-up operation of the accelerator. After the preliminary study using CO2 from 10084,937 soil, which had previously been counted with low-level mini-proportional counters, it became clear that the Toronto accelerator could carry out C-14/C-13/C-12 ratio measurements on 1 gram meteorite and lunar samples and that the C-14 measurements are done with higher precision and better reliability than elsewhere. A collaborative program with the University of Toronto Iso Trace accelerator group, which is expected to be scientifically fruitful. Arrangements have been made for Dr. R.P. Beukens of the Toronto Accelerator Group to extract the carbon compounds from Antarctic meteorite and lunar samples and to convert the compounds to CO2. During the past two years, a uranium-series dating method was developed for polar ice, which method is being applied to ice from the Allan Hills site, Byrd core, and the Beardsmore glacier.

Fireman, E. L.↗

NASA NTRS1986

Mobilization of cryogenic ice in outer solar system satellites

Mechanisms to explain the mobilization of ice on the Uranian satellites Miranda and Ariel at the very low temperatures prevailing on those bodies are considered. A form of pressure solution creep is proposed in which very fine-grained water ice or clathrate hydrate is mobilized by a small amount of intergranular cryogenic fluid (CH4, CO, or N2). Viscosities as low as 10 to the 12th P are possible for a limited time, sufficient to allow flooding of rift valleys and perhaps even substantial lateral flows (glaciers).

Stevenson, D. J.↗

NASA NTRS1987

The Alaska synthetic aperture radar (SAR) facility project

A receiving station for the acquisition and processing of spaceborne synthetic aperture radar (SAR) data is being established by the National Aeronautics and Space Administration (NASA) at the University of Alaska, Fairbanks. The data that will be received from a number of SAR satellites that are to be launched starting in 1990 will allow U.S. researchers to study sea ice, oceanographic and geological features, hydrological processes, glaciers, and vegetation cover in Alaska and its surrounding seas.

Carsey, F.↗

NASA NTRS1988

Assessment of polar climate change using satellite technology

Using results of selected studies, this paper highlights some of the problems that exist in the remote sensing of snow and ice, and demonstrates the importance of remote sensing for the study of snow and ice in determining the effect of temperature increase, due to the atmospheric CO2 increase, on the cryospheric features. Evidence obtained from NOAA, Nimbus, and other satellites, that may already indicate a global or at least a regional warming, includes an increase in permafrost temperature in northern Alaska and the retreat of many of the world's small glaciers in the last 100 years. It is emphasized that remote sensing is of major importance as the method of obtaining data for monitoring future changes in cryospheric features.

Hall, Dorothy K.↗

NASA NTRS1989

Remote sensing of global snowpack energy and mass balance: In-situ measurements on the snow of interior and Arctic Alaska

Observations led to a study of the physical properties of snow and the processes which operate on it. These observations included microwave brightness temperatures in interior Alaska which revealed: (1) up to three times more variability from one cell (1/2 degree latitude x 1/2 degree longitude) to the next in winter than in summer (5 to 15 K in winter and about 5 K in summer); (2) the overall range of temperature from week to week is about seven times greater in winter than in summer; (3) the microwave brightness temperature is about 25 K less than air temperature during summer but 35 to 60 K less during winter; and (4) the presence of snow cover appears to contribute to increasing the difference between air temperature and brightness temperature. The role of irregular substrate under the snow in enhancing convection has been studied with particular attention to variations in snow cover on water surfaces and in forested regions. LANDSAT imagery has been obtained to prepare a classification of ground surface types of the area. The extreme conditions of the 1988 to 1989 winter are discussed with respect to comparing the microwave data sets from 1985, and before, up to the present. The use of the Mt. Wrangell area as aerial photogrammetric controls for glacier measurements is given attention.

Benson, Carl S.↗

NASA NTRS1989

Iridium enrichment in volcanic dust from blue ice fields, Antarctica, and possible relevance to the K/T boundary event

The analysis of samples of volcanic ash dust layers from the Lewis Cliff/Beardmore Glacier in Antarctica shows that some of the samples contain Ir concentrations up to 7.5 ppb. It is shown that the Ir is positively correlated with Se, As, Sb, and other volcanogenic elements. The results show that Ir may be present in some volcanic ash deposits, suggesting that the Ir in the K/T boundary clays is not necessarily of cosmic origin, but may have originated from mantle reservoirs tapped during extensive volcanic eruptions possibly triggered by impact events.

Koeberl, Christian↗

NASA NTRS1989

Early Martian environments - The antarctic and other terrestrial analogs

The comparability of the early environments of Mars and earth, and the biological evolution which occurred on early earth, motivates serious consideration of the possibility of an early Martian biota. Environments which could have contained this early Martian life and which may presently contain evidence of this former life include aquatic, ice, soil, and rock habitats. Several analogs of these potential early Martian environments, which can provide useful information in searching for extinct life on Mars, are currently available for study on earth. These terrestrial analogs include the perennially ice-covered lakes and sandstone rocks in the polar deserts of Antarctica, surface of snowfields and glaciers, desert soils, geothermal springs, and deep subsurface environments.

Wharton, R. A., Jr.↗

NASA NTRS1990

Differential Radar Interferometry Maps Changes In Elevation

Differential radar interferometry uses data from synthetic-aperture radar (SAR). Three passes of SAR yield three amplitude-and-phase images, from which two interferograms (phase-difference images) made. Interferograms used to make third, "double-difference" interferogram indicating vertical motion of terrain between passes. Vertical earthquake motions as small as 1 cm detectable. Used to make extensive, accurate maps of such geophysical phenomena as heaving and buckling in fault zones, motions to tectonic plates, residual displacements from earthquakes, motions from prevolcanic swelling, motions of glaciers, tides, and thermal expansion of mountains from diurnal heating.

Gabriel, Andrew K.↗

NASA NTRS1989

Surface topography of the Greenland Ice Sheet from satellite radar altimetry

Surface elevation maps of the southern half of the Greenland subcontinent are produced from radar altimeter data acquired by the Seasat satellite. A summary of the processing procedure and examples of return waveform data are given. The elevation data are used to generate a regular grid which is then computer contoured to provide an elevation contour map. Ancillary maps show the statistical quality of the elevation data and various characteristics of the surface. The elevation map is used to define ice flow directions and delineate the major drainage basins. Regular maps of the Jakobshavns Glacier drainage basin and the ice divide in the vicinity of Crete Station are presented. Altimeter derived elevations are compared with elevations measured both by satellite geoceivers and optical surveying.

Bindschadler, Robert A.↗

NASA NTRS1990

Cloud and surface textural features in polar regions

The study examines the textural signatures of clouds, ice-covered mountains, solid and broken sea ice and floes, and open water. The textural features are computed from sum and difference histogram and gray-level difference vector statistics defined at various pixel displacement distances derived from Landsat multispectral scanner data. Polar cloudiness, snow-covered mountainous regions, solid sea ice, glaciers, and open water have distinguishable texture features. This suggests that textural measures can be successfully applied to the detection of clouds over snow-covered mountains, an ability of considerable importance for the modeling of snow-melt runoff. However, broken stratocumulus cloud decks and thin cirrus over broken sea ice remain difficult to distinguish texturally. It is concluded that even with high spatial resolution imagery, it may not be possible to distinguish broken stratocumulus and thin clouds from sea ice in the marginal ice zone using the visible channel textural features alone.

Welch, Ronald M.↗

NASA NTRS1990

Testing the Sun-climate Connection with Paleoclimate Data

If there is a significant sun-climate connection, it should be detectable in high-resolution paleoclimate records. Of particular interest is the last few thousand years, where we have both indices of solar variability (C-14 and Be-10) and climate variations (alpine glaciers, tree rings, ice cores, corals, etc.). Although there are a few exceptions, statistical analyses of solar and climate records generally indicates a flickering relationship between the two -- sometimes it seems to be present, sometimes not. The most repeatable solar climate periods occur at approx. 120 and approx. 56 yrs, although there is also evidence for approx. 420 and approx. 200 yrs. power in some records. However, coherence between solar and climate spectra is usually low, and occurrence of solar spectra in climate records is sometimes dependent on choice of analysis program. These results suggest in general a relatively weak sun-climate link on time scales of decades to centuries. This conclusion is consistent with previous studies and with the observation that inferred climate fluctuations of 1.0 to 1.5 C on this time scale would require solar constant variations of approximately 0.5 to 1.0 percent. This change in forcing is almost an order of magnitude greater than observed changes over the last solar cycle and appears to be on the far-outer limit of acceptable changes for a Maunder Minimum-type event.

Crowley, Thomas J.↗

NASA NTRS1990

Earth observing satellite: Understanding the Earth as a system

There is now a plan for global studies which include two very large efforts. One is the International Geosphere/Biosphere Program (IGBP) sponsored by the International Council of Scientific Unions. The other initiative is Mission to Planet Earth, an unbrella program for doing three kinds of space missions. The major one is the Earth Observation Satellite (EOS). EOS is large polar orbiting satellites with heavy payloads. Two will be placed in orbit by NASA, one by the Japanese and one or two by ESA. The overall mission measurement objectives of EOS are summarized: (1) the global distribution of energy input to and energy output from the Earth; (2) the structure, state variables, composition, and dynamics of the atmosphere from the ground to the mesopause; (3) the physical and biological structure, state, composition, and dynamics of the land surface, including terrestrial and inland water ecosystems; (4) the rates, important sources and sinks, and key components and processes of the Earth's biogeochemical cycles; (5) the circulation, surface temperature, wind stress, sea state, and the biological activity of the oceans; (6) the extent, type, state, elevation, roughness, and dynamics of glaciers, ice sheets, snow and sea ice, and the liquid equivalent of snow in the global cryosphere; (7) the global rates, amounts, and distribution of precipitation; and (8) the dynamic motions of the Earth (geophysics) as a whole, including both rotational dynamics and the kinematic motions of the tectonic plates.

Soffen, Gerald↗

NASA NTRS1989

The 1989 NASA-ASEE Summer Faculty Fellowship Program in Aeronautics and Research

The 1989 NASA-ASEE Summer Faculty Fellowship Program at the Goddard Space Flight Center was conducted during 5 Jun. 1989 to 11 Aug. 1989. The research projects were previously assigned. Work summaries are presented for the following topics: optical properties data base; particle acceleration; satellite imagery; telemetry workstation; spectroscopy; image processing; stellar spectra; optical radar; robotics; atmospheric composition; semiconductors computer networks; remote sensing; software engineering; solar flares; and glaciers.

Boroson, Harold R.↗

NASA NTRS1991

Role of artesian groundwater in forming Martian permafrost features

Various landforms possibly related to formation (growth), movement, or decay of ground ice have been identified on Mars, including fretted terrain (ft) and associated lobate debris aprons (lda), the chaotic terrain, concentric crater fills (ccf), polygonal ground, softened terrain, small domes that are possibly pingos, and curvilinear (fingerprint) features (cuf). Glaciers may also have been present. Some of these may involve ice derived from artesian groundwater. Topical areas of discussion are: Mars groundwater and the location of permafrost features; the ft, lda, ccf, and cuf; role of artesian groundwater in formation of fretted terrain, lobate debris blankets, and concentric crater fills; sources of glacial ice; and pingos and other pseudovolcanic structures.

Howard, Alan D.↗

NASA NTRS1991

Terrestrial glacial eskers: Analogs for Martian sinuous ridges

A glacial model was introduced last year for the Argyre region, a concept which is now extended, and which was recently integrated with a Global Hydrologic Model incorporating many other aspects of Martian geology. Despite wide agreement that the Martian ridges strongly resemble glacial eskers, this hypothesis has been presented with great equivocation due to a perceived lack of other glacial landforms. Quite to the contrary, it is shown that the Martian ridges actually do occur in logical ordered sequences with many other types of characteristically glacial appearing landforms. Herein, the esker hypothesis is further supported in isolation from considerations of regional landform assemblages. It is concluded that Martian sinuous ridges are similar in every respect to terrestrial eskers: scale, morphology, planimetric pattern, and associations with other probable glaciogenic landforms. It is found that the esker hypothesis is well supported. Eskers are glaciofluvial structures, and owe their existence to large scale melting of stagnant temporate glaciers. Thus, eskers are indicators of an ameliorating climatic regime after a protracted episode of cold, humid conditions.

Kargel, Jeffrey S.↗