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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
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NASA NTRS1991

Airborne precursor missions in support of SIR-C/X-SAR

The NASA DC-8 and DLR E-SAR airborne imaging radars have been deployed over several sites in Europe and the U.S. in support of SIR-C/X-SAR (Shuttle Imaging Radar-C/X-Synthetic Aperture Radar) science team investigations. To date, data have been acquired in support of studies of alpine glaciers, forests, geology, oceanography, and calibration. An experimental campaign with airborne sensors will take place in Europe in June to July 1991 which will allow multitemporal surveys of several Europeans sites. Current plans are for calibration and ecology experiments to be undertaken in Germany, the Netherlands, Italy, France, and the United Kingdom. Coordinated multitemporal aircraft and ground campaigns are planned in support of hydrology experiments in Italy, the United Kingdom, and Austria. Data will also be acquired in support of oceanogrqhy in the Gulf of Genova, North Atlantic, Straits of Messina and the North Sea. Geology sites will include Campi Flegrei and Vesuvio, Italy.

Evans, D.↗
NASA NTRS1991

An experiment in remote manufacturing using the advanced communications technology satellite

The goal of the completed project was to develop an experiment in remote manufacturing that would use the capabilities of the ACTS satellite. A set of possible experiments that could be performed using the Advanced Communications Technology Satellite (ACTS), and which would perform remote manufacturing using a laser cutter and an integrated circuit testing machine are described in detail. The proposed design is shown to be a feasible solution to the offered problem and it takes into consideration the constraints that were placed on the experiment. In addition, we have developed two more experiments that are included in this report: backup of rural telecommunication networks, and remote use of Synthetic Aperture Radar (SAR) data analysis for on-site collection of glacier scattering data in the Antarctic.

Tsatsoulis, Costas↗
NASA NTRS1991

Alaska Synthetic Aperture Radar (SAR) Facility science data processing architecture

The paper describes the architecture of the Alaska SAR Facility (ASF) at Fairbanks, being developed to generate science data products for supporting research in sea ice motion, ice classification, sea-ice-ocean interaction, glacier behavior, ocean waves, and hydrological and geological study areas. Special attention is given to the individual substructures of the ASF: the Receiving Ground Station (RGS), the SAR Processor System, and the Interactive Image Analysis System. The SAR data will be linked to the RGS by the ESA ERS-1 and ERS-2, the Japanese ERS-1, and the Canadian Radarsat.

Hilland, Jeffrey E.↗
NASA NTRS1991

Applications of the EOS SAR to monitoring global change

The SAR employed by NASA's Earth Observing System (EOS) is a multifrequency multipolarization radar which can conduct global monitoring of geophysical and biophysical parameters. The present discussion of the EOS SAR's role in global monitoring emphasizes geophysical product variables applicable to global hydrologic, biogeochemical, and energy cycle models. EOS SAR products encompass biomass, wetland areas, and phenologic and environmental states, in the field of ecosystem dynamics; soil moisture, snow moisture and extent, and glacier and ice sheet extent and velocity, in hydrologic cycle studies; surface-wave fields and sea ice properties, in ocean/atmosphere circulation; and the topography, erosion, and land forms of the solid earth.

Schier, Marguerite↗
NASA NTRS1992

Changes in ice cover thickness and lake level of Lake Hoare, Antarctica - Implications for local climatic change

Results are reported from 10 years of ice-thickness measurements at perennially ice-covered Lake Hoare in southern Victoria Land, Antarctica. The ice cover of this lake had been thinning steadily at a rate exceeding 20 cm/yr during the last decade but seems to have recently stabilized at a thickness of 3.3 m. Data concerning lake level and degree-days above freezing are presented to show the relationship between peak summer temperatures and the volume of glacier-derived meltwater entering Lake Hoare each summer. From these latter data it is inferred that peak summer temperatures have been above 0 C for a progressively longer period of time each year since 1972. Possible explanations for the thinning of the lake ice are considered. The thickness of the ice cover is determined by the balance between freezing during the winter and ablation that occurs all year but maximizes in summer. It is suggested that the term most likely responsible for the change in the ice cover thickness at Lake Hoare is the extent of summer melting, consistent with the rising lake levels.

Wharton, Robert A., Jr.↗
NASA NTRS1992

Reflectance of snow as measured in situ and from space in sub-arctic areas in Canada and Alaska

An effort is made to measure snow reflectance under different snow and surface conditions, as well as to improve current capabilities for measuring snow reflectance over large regions of space, on the basis of visible and near-IR measurements of clean and dirty snow near Yellowknife, Canada, using both a portable spectrometer and the Landsat TM. Similar measurements were acquired over snow-covered glaciers in Alaska. Visible reflectance of the dirty snow was 30 percent lower than for cleaner snow; the shapes of the reflectance curves were also flatter for the dirty snow. The shape of the reflectance curves and the anisotropic reflectance properties are more useful in differentiating snow type and moisture type than actual reflectances.

Hall, D. K.↗
NASA NTRS1991

Dynamics of the Ross Ice Shelf

The changing flow of the Ross Ice Shelf is described based on AVHRR data from 18 cloud-free images which evince flow stripes and form the data for a glaciological map. The discharge region of the valley glaciers in the Transantarctic Mountains is found to have curvilinear stripes, and the brightness contrast is enhanced to examine the feature. The map of the region also shows rifts, ridge crests, surface folds, and large-scale lineaments.

Casassa, Gino↗
NASA NTRS1992

Sudbury Breccia and suevite as glacial indicators transported 800 km to Kentland Astrobleme, Indiana

A glacial erratic whose place of origin is known by direct comparison with bedrock is known as an indicator. In 1971, while visiting the known astrobleme at Kentland, Indiana, Peredery recognized and sampled in the overlying glacial drift deposits a distinctive boulder of Sudbury suevite (black member, Onaping Formation) that normally occurs within the Sudbury Basin as an impact fall-back or wash-in deposit. The rock was sampled (but later mislaid) from a farmer's cairn next to a cleared field. Informal reports of this discovery prompted the other authors to recently reconnoiter the Kentland locality in an attempt to relocate the original boulder. Several breccia blocks were sampled but laboratory examination proved most of these probably to be diamictites from the Precambrian Gowganda Formation, which outcrops extensively in the southern Ontario. However, one sample was confirmed as typical Sudbury Breccia, which outcrops in the country rock surrounding the Sudbury Basin. Thus two glacial indicators were transported by Pleistocene continental glaciers about 820 km over a tightly proscribed path and, curiously, from one astrobleme to another. Brecciated boulders in the Illinois/Indiana till plain are usually ascribed to the Gowganda or Mississagi formations in Ontario. But impact-generated rocks need not be confused. The carbonaceous matrix of the suevite, for example, was sufficiently distinctive to assign it to the upper portion of the black Onaping. The unique and restricted source area of these indicators provide an accurate and reliable control for estimating Pleistocene ice movement.

Mchone, John F.↗
NASA NTRS1993

Reconstruction of late Wisconsinan Ice Sheet and sea-level implications

The Ross Sea exhibits north-south oriented troughs associated with modern ice streams and outlet glaciers. Seismic reflection profiles across the troughs show evidence that they were glacially eroded. Seismic records show morphologic features interpreted as till tongues, morainal banks, and possibly glacial deltas formed near the grounding line of the former marine ice sheet. Piston cores from the continental shelf penetrated diamictons whose origin and age is problematic. Detailed petrographic analyses of the minerals and rocks comprising these diamictons were conducted to determine subglacial versus glacial marine origin, and to reconstruct the glacial setting of the Ross Sea during the most recent glacial maximum. The most detailed work, conducted in the western Ross Sea, shows that diamictons do occur in distinct petrologic provinces. This is consistent with deposition from the basal debris zone of either an ice sheet or an ice shelf. Overcompaction, in conjunction with the widespread nature of these deposits, favors deposition from marine ice sheets; ice shelves are believed to deposit their basal debris close to the grounding lines. Other results from the investigation are briefly discussed.

Anderson, John B.↗
NASA NTRS1992

Geologic process studies using Synthetic Aperture Radar (SAR) data

The use of SAR data to study geologic processes for better understanding of recent tectonic activity and climate change as well as the mitigation of geologic hazards and exploration for nonrenewable resources is discussed. The geologic processes that are particularly amenable to SAR-based data include volcanism; soil erosion, degradation, and redistribution; coastal erosion and inundation; glacier fluctuations; permafrost; and crustal motions. When SAR data are combined with data from other planned spaceborne sensors including ESA ERS, the Japanese Earth Resources Satellite, and the Canadian Radarsat, it will be possible to build a time-series view of temporal changes over many regions of earth.

Evans, Diane L.↗
NASA NTRS1993

Spatial patterns in backscatter strength across the Greenland Ice Sheet

The relationship between the physical properties of the Greenland ice sheet and Synthetic Aperture Radar (SAR) data collected from aircraft and from ERS-1 is addressed. Limited aircraft data are combined with a description of the glacier surface to predict qualitatively the spatial and seasonal variation in backscatter strength across the ice sheet. In particular the model predicts relatively low backscatter near the ice edge where scattering is dominated by rough surface effects. Backscatter increases through the lake zone as volume scattering becomes important. Strongest backscatter is found in the percolation facies where volume scatter from snow grains and volume scatter from large, buried ice bodies becomes important. Backscatter weakens in the interior ice sheet where fine grained snow is the only mechanism producing backscatter.

Jezek, K. C.↗
NASA NTRS1993

Basal scarp, paleoglacier, and fissure flows of Elysium Mons, Mars

Geological mapping at 1:500,000 scale of the Granicus Valles area west of Elysium Mons (MTM quadrangles 30227, 30222, and 25227) indicates that (1) the oldest deposits in the area are Upper Hesperian lavas of the Elysium shield; (2) a basal scarp formed by Early Amazonian faulting around the northwest flank of Elysium Mons triggered growth of Elysium Fossae; (3) a glacier or an ice sheet west and north of the scarp was of long duration; (4) water and lava flows from Elysium Fossae became dominant during and after glacial recession; and (5) the last volcanic-fissure-related flows resulted in linear chains of small domes on the Elysium shield.

Chapman, Mary G.↗
NASA NTRS1993

Research on Earth's rotation and the effect of atmospheric pressure on vertical deformation and sea level variability

The work done under NASA grant NAG5-485 included modelling the deformation of the earth caused by variations in atmospheric pressure. The amount of deformation near coasts is sensitive to the nature of the oceanic response to the pressure. The PSMSL (Permanent Service for Mean Sea Level) data suggest the response is inverted barometer at periods greater than a couple months. Green's functions were constructed to describe the perturbation of the geoid caused by atmospheric and oceanic loading and by the accompanying load-induced deformation. It was found that perturbation of up to 2 cm are possible. Ice mass balance data was used for continental glaciers to look at the glacial contributions to time-dependent changes in polar motion, the lod, the earth's gravitational field, the position of the earth's center-of-mass, and global sea level. It was found that there can be lateral, non-hydrostatic structure inside the fluid core caused by gravitational forcing from the mantle, from the inner core, or from topography at the core/mantle or inner core/outer core boundaries. The nutational and tidal response of a non-hydrostatic earth with a solid inner core was modeled. Monthly, global tide gauge data from PSMSL was used to look at the 18.6-year ocean tide, the 14-month pole tide, the oceanic response to pressure, the linear trend and inter-annual variability in the earth's gravity field, the global sea level rise, and the effects of post glacial rebound. The effects of mantle anelasticity on nutations, earth tides, and tidal variation in the lod was modeled. Results of this model can be used with Crustal Dynamics observations to look at the anelastic dissipation and dispersion at tidal periods. The effects of surface topography on various components of crustal deformation was also modeled, and numerical models were developed of post glacial rebound.

Wahr, John↗
NASA NTRS1993

Ice in the northern plains: Relic of a frozen ocean?

Viking images revealed many features in the northern plains and along their boundary that early investigators believed to be formed by ice-related processes. The features are possible pingos, pseudocraters, table mountains and moberg ridges, thermokarst depressions, moraines, patterned ground, and lobate aprons that suggest viscous flow such as that of ice or rock glaciers. More recently, many of these features were reinterpreted as related to sedimentation in hypothetical former polar lakes, oceans, or alluvial plains or as shoreline features of associated water bodies. Some evidence that points toward the existence of former bodies of standing water in the northern plains, but is also consistent with the idea that these bodies were ice covered or completely frozen is reviewed.

Lucchitta, B. K.↗
NASA NTRS1993

The thumbprint terrain: What will Mars Observer tell us?

Some of the more puzzling features seen on Mars are those known as curvilinear features or 'thumb print' terrain, types of patterned ground found in the northern plains. The thumbprint terrain, named for its resemblance to the lines of a human thumbprint is found on what appears to be level, relatively low-lying ground near the crustal dichotomy boundary. It is often found near the termini of large channels. There are three types of thumbprint terrain in the classification of Rossbacher and Judson. The first consists of ridges and depressions about a kilometer wide, separated by a few kilometers, and with an apparent relief of 40-100 m. The second consists of steep-sided, flat-floored depressions about a kilometer wide, separated by a few kilometers, and with an apparent relief of 10-290 m. The third consists only of albedo markings, with a typical scale of about a kilometer. Many models were proposed to explain the origin of this terrain. It was suggested that it was caused by lava flows, removal of debris mantles, glaciers, or karst. However, the most popular models at present involve the action of subsurface ice to form such thermokarst features as striped ground, solifluction lobes, and/or linear, ice-cored ridges. There are several instruments on the Mars Observer spacecraft that will be able to provide us with information useful in distinguishing between these models.

Schaefer, M. W.↗
NASA NTRS1993

Radar backscattering from snow facies of the Greenland ice sheet: Results from the AIRSAR 1991 campaign

In June 1991, the NASA/JPL airborne SAR (AIRSAR) acquired C- (lambda = 5.6cm), L- (lambda = 24cm), and P- (lambda = 68m) band polarimetric SAR data over the Greenland ice sheet. These data are processed using version 3.55 of the AIRSAR processor which provides radiometrically and polarimetrically calibrated images. The internal calibration of the AIRSAR data is cross-checked using the radar response from corner reflectors deployed prior to flight in one of the scenes. In addition, a quantitative assessment of the noise power level at various frequencies and polarizations is made in all the scenes. Synoptic SAR data corresponding to a swath width of about 12 by 50 km in length (compared to the standard 12 x 12 km size of high-resolution scenes) are also processed and calibrated to study transitions in radar backscatter as a function of snow facies at selected frequencies and polarizations. The snow facies on the Greenland ice sheet are traditionally categorized based on differences in melting regime during the summer months. The interior of Greenland corresponds to the dry snow zone where terrain elevation is the highest and no snow melt occurs. The lowest elevation boundary of the dry snow zone is known traditionally as the dry snow line. Beneath it is the percolation zone where melting occurs in the summer and water percolates through the snow freezing at depth to form massive ice lenses and ice pipes. At the downslope margin of this zone is the wet snow line. Below it, the wet snow zone corresponds to the lowest elevations where snow remains at the end of the summer. Ablation produces enough meltwater to create areas of snow saturated with water, together with ponds and lakes. The lowest altitude zone of ablation sees enough summer melt to remove all traces of seasonal snow accumulation, such that the surface comprises bare glacier ice.

Rignot, Eric↗
NASA NTRS1993

Interferometric detection of freeze-thaw displacements of Alaskan permafrost using ERS-1 data

The possibility of making large scale (50 km) measurements of motions of the earth's surface with high resolution (10 m) and very high accuracy (1 cm) from multipass SAR interferometry was established in 1989. Other experiments have confirmed the viability and usefulness of the method. Work is underway in various groups to measure displacements from volcanic activity, seismic events, glacier motion, and in the present study, freeze-thaw cycles in Alaskan permafrost. The ground is known to move significantly in these cycles, and provided that freezing does not cause image decorrelation, it should be possible to measure both ground swelling and subsidence. The authors have obtained data from multiple passes of ERS-1 over the Toolik Lake region of northern Alaska of suitable quality for interferometry. The data are processed into images, and single interferograms are formed in the usual manner. Phase unwrapping is performed, and the multipass baselines are estimated from the images using both orbit ephemerides and scene tie points. The phases are scaled by the baseline ratio, and a double-difference interferogram (DDI) is formed. It is found that there is a residual 'saddle-shape' phase error across the image, which is postulated to be caused by a small divergence (10(exp -2) deg.) in the orbits. A simulation of a DDI from divergent orbits confirms the shape and magnitude of the error. A two-dimensional least squares fit to the error is performed, which is used to correct the DDI. The final, corrected DDI shows significant phase (altitude) changes over the period of the observation.

Werner, Charles L.↗
NASA NTRS1993

Ancient Martian valley genesis and paleoclimatic inference: The present as a key to the past

I offer here the speculative genetic hypothesis that the flat-floored landforms represent episodically active, sediment-laden valley glaciers formed by localized geothermal melting of abundant interstitial ice (permafrost) in a fine-grained sedimentary terrain. Geothermal melting may also localize spring heads for the narrow deep, high-gradient valleys, or the collapse process itself may result in the generation of decanted, relatively sediment-poor overland water flows (some local evidence of fluid overtopping of the localized depressions exists). Whatever the generic mechanisms for the suite of valley landforms, perhaps the most interesting observation is simply their youth. In aggregate, the morphologies are similar to the ancient valley systems cited as evidence for a previously much denser atmosphere on Mars.

Brakenridge, G. R.↗