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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Velocities of Thwaites and Land glaciers

Changes in the area of volume of polar ice sheets are intricately linked to changes in global climate and may severely impact the densely populated coastal regions on Earth. An ice sheet's velocity is a critical parameter, which, together with ice thickness, allows the determination of discharge rates. Using moderate-resolution satellite images such as Landsat, the velocity of floating ice can be measured quickly and relatively inexpensively by tracing crevasse patterns on shelves and ice tongues. Errors in measured velocities are as little as 0.02 km per year, if the following criteria are met: (1) the time interval is longer than 10 years; (2) the velocity is higher than 0.5 km per year; (3) the coregistration points are well dispersed and enclose the area to be measured; and (4) the image pair includes a Landsat 4 or 5 image. The fewer of these conditions that are met, the less accurate the results become; but even for poor conditions, the velocities are generally reliable to near 0.1 km per year. We are in the process of obtaining velocities of all ice shelves and ice tongues along the Bakutis and Ruppert coasts, wherever suitable crevasse patterns exist. So far, we have obtained velocities for the Thwaites and Land glacier tongues.

Lucchitta, B. K.↗
NASA NTRS1994

Application of artificial neural networks in hydrological modeling: A case study of runoff simulation of a Himalayan glacier basin

The simulation of runoff from a Himalayan Glacier basin using an Artificial Neural Network (ANN) is presented. The performance of the ANN model is found to be superior to the Energy Balance Model and the Multiple Regression model. The RMS Error is used as the figure of merit for judging the performance of the three models, and the RMS Error for the ANN model is the latest of the three models. The ANN is faster in learning and exhibits excellent system generalization characteristics.

Buch, A. M.↗
NASA NTRS2000

High-Latitude Martian Impact Paleolakes: The Possible Contribution of Snowfall and Ancient Glaciers in the Lacustrine Activity Associated to Argyre and Hellas

Hellas and Argyre show impact crater paleolakes, which morphologies could have been associated to glacial and sub-glacial processes, implying the existence of snowfall and ancient glaciers. Some of them show as well a hydrothermal contribution related to the presence of volcanic centers. Additional information is contained in original extended abstract.

Cabrol, N. A.↗
NASA NTRS2002

Comparative Results of Using Different Methods for Discovery of Microorganisms in very Ancient Layers of the Central Antarctic Glacier above the Lake Vostok

The ice sheet of the Central Antarctic is considered by the scientific community worldwide, as a model to elaborate on different methods to search for life outside Earth. This became especially significant in connection with the discovery of the underglacial lake in the vicinity of the Russian Antarctic Station Vostok. Lake Vostok is considered by many scientists as an analog of the ice covered seas of Jupiter's satellite Europa. According to the opinion of many researchers there is the possibility that relict forms of microorganisms, well preserved since the Ice Age, may be present in this lake. Investigations throughout the thickness of the ice sheet above Lake Vostok show the presence of microorganisms belonging to different well-known taxonomic groups, even in the very ancient horizons near close to floor of the glacier. Different methods were used to search for microorganisms that are rarely found in the deep ancient layers of an ice sheet. The method of aseptic sampling from the ice cores and the results of controlled sterile conditions in all stages when conducting these investigations, are described in detail in previous reports. Primary investigations tried the usual methods of sowing samples onto different nutrient media, and the result was that only a few microorganisms grew on the media used. The possibility of isolating the organisms obtained for further investigations, by using modern methods including DNA-analysis, appears to be the preferred method. Further investigations of the very ancient layers of the ice sheet by radioisotopic, luminescence, and scanning electron microscopy methods at different modifications, revealed the quantity and morphological diversity of the cells of microorganisms that were distributed on the different horizons. Investigations over many years have shown that the microflora in the very ancient strata of the Antarctic ice cover, nearest to the bedrock, support the effectiveness of using a combination of different methods to search for signs of life in ancient icy formations, which might play a role in the long-term preservation and transportation of microbial life throughout the Universe.

Abyzov, S. S.↗
NASA NTRS2007

Radar Interferometer for Topographic Mapping of Glaciers and Ice Sheets

A report discusses Ka-band (35-GHz) radar for mapping the surface topography of glaciers and ice sheets at high spatial resolution and high vertical accuracy, independent of cloud cover, with a swath-width of 70 km. The system is a single- pass, single-platform interferometric synthetic aperture radar (InSAR) with an 8-mm wavelength, which minimizes snow penetration while remaining relatively impervious to atmospheric attenuation. As exhibited by the lower frequency SRTM (Shuttle Radar Topography Mission) AirSAR and GeoSAR systems, an InSAR measures topography using two antennas separated by a baseline in the cross-track direction, to view the same region on the ground. The interferometric combination of data received allows the system to resolve the pathlength difference from the illuminated area to the antennas to a fraction of a wavelength. From the interferometric phase, the height of the target area can be estimated. This means an InSAR system is capable of providing not only the position of each image point in along-track and slant range as with a traditional SAR but also the height of that point through interferometry. Although the evolution of InSAR to a millimeter-wave center frequency maximizes the interferometric accuracy from a given baseline length, the high frequency also creates a fundamental problem of swath coverage versus signal-to-noise ratio. While the length of SAR antennas is typically fixed by mass and stowage or deployment constraints, the width is constrained by the desired illuminated swath width. As the across-track beam width which sets the swath size is proportional to the wavelength, a fixed swath size equates to a smaller antenna as the frequency is increased. This loss of antenna size reduces the two-way antenna gain to the second power, drastically reducing the signal-to-noise ratio of the SAR system. This fundamental constraint of high-frequency SAR systems is addressed by applying digital beam-forming (DBF) techniques to synthesize multiple simultaneous receive beams in elevation while maintaining a broad transmit illumination. Through this technique, a high antenna gain on receive is preserved, thereby reducing the required transmit power and thus enabling high-frequency SARs and high-precision InSAR from a single spacecraft.

Moller, Delwyn K.↗
NASA NTRS2011

Variability of Basal Melt Beneath the Pine Island Glacier Ice Shelf, West Antarctica

Observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the Pine Island Glacier ice shelf, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest ice-shelf-wide changes to the ocean s influence on the ice shelf as the grounding line retreated. Longitudinal profiles of ice surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40.5 Gt/a. One profile captures a persistent set of surface waves that correlates with quasi-annual variations of atmospheric forcing of Amundsen Sea circulation patterns, establishing a direct connection between atmospheric variability and sub-ice-shelf melting. Ice surface troughs are hydrostatically compensated by ice-bottom voids up to 150m deep. Voids form dynamically at the grounding line, triggered by enhanced melting when warmer-than-average water arrives. Subsequent enlargement of the voids is thermally inefficient (4% or less) compared with an overall melting efficiency beneath the ice shelf of 22%. Residual warm water is believed to cause three persistent polynyas at the ice-shelf front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.

Bindschadler, Robert↗
NASA NTRS2021

Radar-Sounding Characterization of the Subglacial Groundwater Table Beneath Hiawatha Glacier, Greenland

Radar-sounding surveys associated with the discovery of a large impact crater beneath Hiawatha Glacier, Greenland, revealed bright, flat subglacial reflections hypothesized to originate from a subglacial groundwater table. We test this hypothesis using radiometric and hydrologic analysis of those radar data. The dielectric loss between the reflection from the top of the basal layer and subglacial reflection and their reflectivity difference represent dual constraints upon the complex permittivity of the basal material. Either ice-cemented debris or fractured, well-drained bedrock explain the basal layer's radiometric properties. The subglacial reflector's geometry is parallel to isopotential hydraulic head contours, located 7.5–15.3 m below the interface, and 11 ± 7 dB brighter than the ice–basal layer reflection. We conclude that this subglacial reflection is a groundwater table and that its detection was enabled by the wide bandwidth of the radar system and unusual geologic setting, suggesting a path for future direct radar detection of subglacial groundwater elsewhere.

Johnathan T. Bessette↗