Search NASA⌕ Search

SEARCH · Search NASA

Results for “ice flows”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A scanning radar altimeter for mapping continental topography

Topographic information constitutes a fundamental data set for the Earth sciences. In the geological and geophysical sciences, topography combined with gravitational information provides an important constraint on the structure and rheologic properties of the crust and lithosphere. Detailed topography data can also be used to map offsets associated with faulting and to reveal the effects of tectonic deformation. In the polar regions, elevation data form a crucial but as yet largely unavailable resource for studying ice sheet mass balance and ice flow dynamics. The vast Antarctic ice sheet is the largest fresh water reservoir on Earth and is an important influence on ocean circulation and global climate. However, our knowledge of its stability is so limited that we cannot even specify whether the Antarctic ice sheet is growing or shrinking. It is clear that there is need for high quality global topography data. A summary of potential applications with their resolution requirements is shown.

Dixon, T. H.↗
NASA NTRS1988

Observed velocity fluctuations on a major Antarctic ice stream

Recent ice velocity measurements on the major Antarctic Ice Stream B are compared with those collected 10 years ago. The results show that the ice flow in the mouth of Ice Stream B has decelerated by about 20 percent. The possible causes of this deceleration are discussed on the basis of present knowledge of current regional dynamics, and the possible effects of this deceleration on future ice stream behavior are examined.

Stephenson, S. N.↗
NASA NTRS1993

Observation of pressure ridges in SAR images of sea ice: Scattering theory and comparison with observations

Ridges and keels (hummocks and bummocks) in sea ice flows are important in sea ice research for both scientific and practical reasons. Sea ice movement and deformation is driven by internal and external stresses on the ice. Ridges and keels play important roles in both cases because they determine the external wind and current stresses via drag coefficients. For example, the drag coefficient over sea ice can vary by a factor of several depending on the fluid mechanical roughness length of the surface. This roughness length is thought to be strongly dependent on the ridge structures present. Thus, variations in ridge and keel structure can cause gradients in external stresses which must be balanced by internal stresses and possibly fracture of the ice. Ridging in sea ice is also a sign of fracture. In a practical sense, large ridges form the biggest impediment to surface travel over the ice or penetration through sea ice by ice-strengthened ships. Ridges also play an important role in the damage caused by sea ice to off-shore structures. Hence, observation and measurement of sea ice ridges is an important component of sea ice remote sensing. The research reported here builds on previous work, estimating the characteristics of ridges and leads in sea ice from SAR images. Our objective is to develop methods for quantitative measurement of sea ice ridges from SAR images. To make further progress, in particular, to estimate ridge height, a scattering model for ridges is needed. Our research approach for a ridge scattering model begins with a survey of the geometrical properties of ridges and a comparison with the characteristics of the surrounding ice. For this purpose we have used airborne optical laser (AOL) data collected during the 1987 Greenland Sea Experiment. These data were used to generate a spatial wavenumber spectrum for height variance for a typical ridge - the typical ridge is the average over 10 large ridges. Our first-order model radar scattering includes both the quasi-specular and Bragg resonant scatter mechanisms. This model is extended to include contributions from volume scatter and scatter from discrete objects. Geometrical characteristics from the AOL survey and model calculations imply that for radar wavelengths and observation geometries that are dominated by the quasi-specular scattering mechanism radar backscatter from a ridge is a measure of peak ridge height. We present scattering model results and compare them with ridges observed during the LEADEX experiment of March-April 1992 when both X, C, and L-band aircraft SAR and the ERS-1 satellite SAR observed a region in the Beaufort Sea near 86 deg N, 10 deg W. Data were also collected documenting ridge characteristics on the surface. The surface data are used to generate a SAR signature via the scattering model described above. The predicted SAR signatures compare well with the SAR observations.

Vesecky, J. F.↗
NASA NTRS2007

Increased Water Storage at Ice-stream Onsets: A Critical Mechanism?

The interdependence of rapid ice flow, surface topography and the spatial distribution of subglacial water are examined by linking existing theories. The motivation is to investigate whether the acceleration of an ice-stream tributary contains a positive feedback that encourages the retention of subglacial water that leads to faster flow. Periodically varying surface and bed topographies are related through a linear ice-flow perturbation theory for various values of mean surface slope, perturbation amplitude and basal sliding speeds. The topographic variations lead to a periodic variation in hydraulic potential that is used to infer the tendency for subglacial water to be retained in local hydraulic potential minima. If water retention leads to enhanced basal sliding, a positive feedback loop is closed that could explain the transition from slower tributary flow to faster-streaming flow and the sustained downstream acceleration along the tributary-ice-stream system. A sensitivity study illustrates that the same range of topographic wavelengths most effectively transmitted from the bed to the surface also strongly influences the behavior of subglacial water. A lubrication index is defined to qualitatively measure the heterogeneity of the subglacial hydrologic system. Application of this index to field data shows that the transition from tributary to ice stream closely agrees with the location where subglacial water may be first stored.

Bindschadler, Robert↗
NASA NTRS2021

Topographic Correction of Geothermal Heat Flux in Greenland and Antarctica

Earth’s thick, polar ice sheets insulate the bedrock beneath them from the colder temperatures at the ice surface. Consequently, the small amount of geothermal heat that Earth’s bedrock releases can have a disproportionate role in controlling ice flow. Geothermal heat flux measurements beneath ice sheets are sparse, and models do not presently account for variable bed topography. Here, we present a simple statistical method for correcting geothermal heat flux models to make them consistent with known subglacial bed topography. This method is based on previous geothermal heat flux measurements across valleys and ridges, and it helps us explore the broader significance of geothermal heat flux variability beneath the Greenland and Antarctic ice sheets. Our method can also be used to estimate the influence of topography on geothermal heat flux in non-ice-covered areas.

William Colgan↗
NASA NTRS2017

The Effect of Firn-Aquifer Drainage on the Greenland Subglacial System or Subglacial Efficiency and Storage Modified by the Temporal Pattern of High-Elevation Meltwater Input

Ice flow in marginal region of the Greenland Ice Sheet dynamically responds to summer melting as surface meltwater is routed through the supraglacial hydrologic system to the bed of the ice sheet via crevasses and moulins. Given the expected increases in surface melt production and extent, and the potential for high elevation surface-to-bed connections, it is imperative to understand how meltwater delivered to the bed from different high-elevation supraglacial storage features affects the evolution of the subglacial hydrologic system and associated ice dynamics. Here, we use the two-dimensional subglacial hydrologic model, GLaDS, which includes distributed and channelized water flow, to test how the subglacial system of an idealized outlet glacier responds to cases of high-elevation firn-aquifer-type and supraglacial-lake-type englacial drainage over the course of 5 years. Model outputs driven by these high elevation drainage types are compared to steady-state model results, where the subglacial system only receives the 1980- 2016 mean MERRA-2 runoff via low-elevation moulins. Across all experiments, the subglacial hydrologic system displays inter-annual memory, resulting in multiyear declines in subglacial pressure during the onset of seasonal melting and growth of subglacial channels. The gradual addition of water in firn-aquifer-type drainage scenarios resulted in small increases in subglacial water storage but limited changes in subglacial efficiency and channelization. Rapid, supraglacial- lake-type drainage resulted in short-term local increases in subglacial water pressure and storage, which gave way to spatially extensive decreases in subglacial pressure and downstream channelization. These preliminary results suggest that the character of high-elevation englacial drainage can have a strong, and possibly outsized, control on subglacial efficiency throughout the ablation zone. Therefore, understanding both how high elevation meltwater is stored supraglacially and the probability of crevassing at high elevations will play an important role in how the subglacial system, proglacial discharge and ice motion will respond to future increases in surface melt production and runoff.

Andrews, Lauren C.↗
NASA NTRS1979

Remote sensing of snow and ice

This paper reviews remote sensing of snow and ice, techniques for improved monitoring, and incorporation of the new data into forecasting and management systems. The snowcover interpretation of visible and infrared data from satellites, automated digital methods, radiative transfer modeling to calculate the solar reflectance of snow, and models using snowcover input data and elevation zones for calculating snowmelt are discussed. The use of visible and near infrared techniques for inferring snow properties, microwave monitoring of snowpack characteristics, use of Landsat images for collecting glacier data, monitoring of river ice with visible imagery from NOAA satellites, use of sequential imagery for tracking ice flow movement, and microwave studies of sea ice are described. Applications of snow and ice research to commercial use are examined, and it is concluded that a major problem to be solved is characterization of snow and ice in nature, since assigning of the correct properties to a real system to be modeled has been difficult.

Rango, A.↗
NASA NTRS1984

Observing the polar regions from space

The use of active and passive microwave sensors to provide information on the ice cover in the earth's polar regions is described, along with the ice characteristics that can be measured by such techniques. The continental ice sheets of Greenland and Antarctica represent vast reservoirs of fresh water that can significantly impact sea level if the ice sheets are changing in size. Satellite remote sensing gives information on: sea ice extent and physical characteristics; detailed images of ice flows and open-water leads within the ice pack; sea-ice movement; zones of summer melting and snow-accumulation rates on the continental ice sheets; accurate estimates of ice-surface elevation and detection of zones on the ice sheet that are either thickening or thinning; accurate, all-weather mapping of ice coastlines and large crevasses, and estimates of ice discharge rates from the ice sheets.

Thomas, R. H.↗
NASA NTRS1988

Ice sheet radar altimetry

The surface topography of the Greenland and Antarctic ice sheets between 72 degrees north and south was mapped using radar altimetry data from the U.S. Navy GEOSAT. The glaciological objectives of this activity were to study the dynamics of the ice flow, changes in the position of floating ice-shelf fronts, and ultimately to measure temporal changes in ice surface elevation indicative of ice sheet mass balance.

Zwally, J.↗
NASA NTRS2021

Acoustic Sensor Network for Planetary Exploration

This paper investigates the concept of an acoustic sensor network that can monitor a variety of geophysical processes occurring on other planetary bodies. In many cases sound is naturally omnidirectional and travels at known speeds which depend on the composition and density of the atmosphere. The differences in the time of flight of signals received by a distributed microphone network can be used to locate the source of the sound. We suggest this property is ideal for mobile planetary robots and can be used to expand the exploration envelope considerably by directing camera pointing or rover path planning thus extending beyond line-of-sight exploration. Acoustic signatures have been used in a variety of fields (e.g., sonar, heavy machinery) to identify and catalog sounds associated with a specific vessels and malfunctioning machinery. Our ears have cataloged hundreds of sounds and we continuously use these sounds both consciously and subconsciously to extract information about our surroundings. This paper investigates the use acoustic measurements on other planetary bodies that could be used to characterize specific environmental parameters such as rain droplet size, wind speed, thunder, or dust devil vortex diameter. The paper identified other important sound sources that are thought to occur on other bodies in our solar system include; booming or singing dunes, waves, rivers, streams, fluidfalls, geysers, hurricanes, tornados, ice flow, volcanoes, planetary quakes, avalanche, rock slides and ice cracking. In addition, this paper focused on issues associated with the development of appropriate sensors for the network including the specification of the sensitivity, frequency response, and directional response of each of the microphones in the network in order to aid in localization of sound sources. We also presented our initial development of the transducers for potential mission targets including Mars and Titan and investigated the use of signal processing techniques including windowing, time frequency plots and correlation techniques to resolve phase differences between sensors in the network to aid in localization. We also identified additional benefits of these sensor networks in that they could used as engineering sensors to diagnose mechanical malfunctions on a rover or lander actuators or mechanisms. We also noted that they could also enhance public outreach by adding sound to videos.

Malaska, Mike↗
NASA NTRS2003

The Effects of Snow Depth Forcing on Southern Ocean Sea Ice Simulations

The spatial and temporal distribution of snow on sea ice is an important factor for sea ice and climate models. First, it acts as an efficient insulator between the ocean and the atmosphere, and second, snow is a source of fresh water for altering the already weak Southern Ocean stratification. For the Antarctic, where the ice thickness is relatively thin, snow can impact the ice thickness in two ways: a) As mentioned above snow on sea ice reduces the ocean-atmosphere heat flux and thus reduces freezing at the base of the ice flows; b) a heavy snow load can suppress the ice below sea level which causes flooding and, with subsequent freezing, a thickening of the sea ice (snow-to-ice conversion). In this paper, we compare different snow fall paramterizations (incl. the incorporation of satellite-derived snow depth) and study the effect on the sea ice using a sea ice model.

Powel, Dylan C.↗
NASA NTRS2024

Geologic Provinces Beneath the Greenland Ice Sheet Constrained by Geophysical Data Synthesis

Present understanding of Greenland's subglacial geology is derived mostly from interpolation of geologic mapping of its ice-free margins and unconstrained by geophysical data. Here we refine the extent of its geologic provinces by synthesizing geophysical constraints on subglacial geology from seismic, gravity, magnetic and topographic data. North of 72°N, no province clearly extends across the whole island, leaving three distinct subglacial regions yet to be reconciled with margin geology. Geophysically coherent anomalies and apparent province boundaries are adjacent to the onset of faster ice flow at both Petermann Glacier and the Northeast Greenland Ice Stream. Separately, based on their subaerial expression, dozens of unusually long, straight and sub-parallel subglacial valleys cross Greenland's interior and are not yet resolved by current syntheses of its subglacial topography.

Joseph A. MacGregor↗
NASA NTRS2019

Possible Role for Tectonics in the Evolving Stability of the Greenland Ice Sheet

The history of the Greenland Ice Sheet has been influenced by the geodynamic response to ice sheet fluctuations, and this interaction may help explain past deglaciations under modest climate forcing. We hypothesize that when the Iceland hot spot passed beneath north‐central Greenland, it thinned the lithosphere and left anomalous heat likely with partially melted rock; however, it did not break through the crust to supply voluminous flood basalts. Subsequent Plio‐Pleistocene glacial‐interglacial cycles caused large and rapidly migrating stresses, driving dike formation and other processes that shifted melted rock toward the surface. The resulting increase in surface geothermal flux favored a thinner, faster‐responding ice sheet that was more prone to deglaciation. If this hypothesis of control through changes in geothermal flux is correct, then the long‐term (10 (sup 5) to 10 (sup 6) years) trend now is toward lower geothermal flux, but with higher‐frequency (less than or equal to 10( sup 4) to 10 (sup 5) years) oscillations linked to glacial‐interglacial cycles. Whether the geothermal flux is increasing or decreasing now is not known but is of societal relevance due to its possible impact on ice flow. We infer that projections of the future of the ice sheet and its effect on sea level must integrate geologic and geophysical data as well as glaciological, atmospheric, oceanic, and paleoclimatic information.

Greenland Ice Sheet↗
NASA NTRS1993

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

Multi-temporal satellite images, field observations, and field measurements were used to investigate the mechanisms by which sea ice melts offshore from the Mackenzie River delta. Advanced Very High Resolution Radiometer (AVHRR) satellite data recorded in 1986 were analyzed. The satellite data were geometrically corrected and radiometrically calibrated so that albedo and temperature values could be extracted. The investigation revealed that sea ice melted approximately 2 weeks earlier offshore from the Mackenzie River delta than along coasts where river discharge is minimal or non-existent. There is significant intra-delta variability in the timing and patterns of ice melt. An estimation of energy flux indicates that 30 percent more of the visible wavelength energy and 25 percent more of the near-infrared wavelength energy is absorbed by water offshore of the delta compared to coastal areas with minimal river discharge. The analysis also revealed that the removal of sea ice involves the following: over-ice-flooding along the coast offshore from river delta channels; under-ice flow of 'warm' river water; melting and calving of the fast ice; and, the formation of a bight in the pack ice edge. Two stages in the melting of sea ice were identified: (1) an early stage where heat is supplied to overflows largely by solar radiation, and (2) a later stage where heat is supplied by river discharge in addition to solar radiation. A simple thermodynamic model of the thaw process in the fast ice zone was developed and parameterized based on events recorded by the satellite images. The model treats river discharge as the source of sensible heat at the base of the ice cover. The results of a series of sensitivity tests to assess the influence of river discharge on the near shore ice are presented.

Dean, Kenneson G.↗
NASA NTRS2021

A first constraint on basal melt-water production of the Greenland ice sheet

The Greenland ice sheet has been one of the largest sources of sea-level rise since the early 2000s. However, basal melt has not been included explicitly in assessments of ice-sheet mass loss so far. Here, we present the first estimate of the total and regional basal melt produced by the ice sheet and the recent change in basal melt through time. We find that the ice sheet’s present basal melt production is 21.4 +4.4/−4.0 Gt per year, and that melt generated by basal friction is responsible for about half of this volume. We estimate that basal melting has increased by 2.9 ± 5.2 Gt during the first decade of the 2000s. As the Arctic warms, we anticipate that basal melt will continue to increase due to faster ice flow and more surface melting thus compounding current mass loss trends, enhancing solid ice discharge, and modifying fjord circulation.

Greenland Ice Sheet↗
NASA NTRS2004

Numerical Modeling of Glaciers in Martian Paleoclimates

Numerous geologic features suggest the presence of ice flow on the surface of mars. These features include lobate debris aprons, concentric crater fill, and lineated valley fill. The lateral extent of these features can range from 100 meters to over 20 km. Previous work has demonstrated that these features could not have formed in current Martian conditions. It has long been speculated that changes in Mars orbital properties, namely its obliquity, eccentricity, and argument of perihelion, can result in dramatic changes to climate. Recent climate model studies have shown that at periods of increased obliquity north polar water ice is mobilized southward and deposited at low ad mid latitudes. Mid latitude accumulation of ice would provide the necessary conditions for rock glaciers to form. A time-marching, finite element glacier model is used to demonstrate the ability of ice and ice-rock mixtures to flow under Martian paleoclimate conditions. Input to this model is constrained by the NASA Ames Mars General Circulation Model (MGCM).

Colaprete, A.↗
NASA NTRS2000

Sea Ice Motion from Wavelet Analysis of Satellite Data

Wavelet analysis of NASA scatterometer (NSCAT) backscatter and Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) radiance data can be used to obtain daily sea ice drift information for the Arctic region. This technique provides improved spatial coverage over the existing array of Arctic Ocean buoys and better temporal resolution over techniques utilizing data from satellite synthetic aperture radars. Comparisons with ice motion derived from ocean buoys give good quantitative agreement. Both comparison results from NSCAT and SSM/I are compatible, and the results from NSCAT can definitely complement that from SSM/I when there are cloud or surface effects. Then three sea-ice drift daily results from NSCAT, SSM/I, and buoy data can be merged as a composite map by some data fusion techniques. The ice flow streamlines are highly correlated with surface air pressure contours. Examples of derived ice-drift maps in December 1996 illustrate large-scale circulation reversals over a period of four days. A method for deriving divergence and shear at the large-scale has been developed and comparison between buoys and satellite results shows a good agreement. These calibrated/validated results indicate that NSCAT, SSM/I merged daily ice motion are suitably accurate to identify and closely locate sea ice processes, and to improve our current knowledge of sea ice drift and related processes through the data assimilation of ocean-ice numerical model. For demonstration purpose, the ice velocities derived from satellite data are compared with the ice velocities derived from a coupled ice-ocean interaction model. The comparison reveals that the general circulation patterns of the two are quite similar but the ice velocity differences between the two are quite significant. In order to quantify the wind effects on ice motion, empirical orthogonal functions (EOF) are used in the principal component analysis for both ice motion and pressure field. Some preliminary results of sea-ice motion from QuikScat will also be presented.

Liu, Antony K.↗
NASA NTRS2021

Challenges in predicting Greenland supraglacial lake drainages at the regional scale

A leading hypothesis for the mechanism of fast supraglacial lake drainages is that transient extensional stresses briefly allow crevassing in otherwise compressional ice flow regimes. Lake water can then hydrofracture a crevasse to the base of the ice sheet, and river inputs can maintain this connection as a moulin. If future ice sheet models are to accurately represent moulins, we must understand their formation processes, timescales, and locations. Here, we use remote-sensing velocity products to constrain the relationship between strain rates and lake drainages across ∼ 1600 ksq.m in Pâkitsoq, western Greenland, between 2002–2019. We find significantly more extensional background strain rates at moulins associated with fast-draining lakes than at slow-draining or non-draining lake moulins. We test whether moulins in more extensional background settings drain their lakes earlier, but we find insignificant correlation. To investigate the frequency at which strain-rate transients are associated with fast lake drainage, we examined Landsat-derived strain rates over 16 and 32 d periods at moulins associated with 240 fast-lake-drainage events over 18 years. A low signal-to-noise ratio, the presence of water, and the multi-week repeat cycle obscured any resolution of the hypothesized transient strain rates. Our results support the hypothesis that transient strain rates drive fast lake drainages. However, the current generation of ice sheet velocity products, even when stacked across hundreds of fast lake drainages, cannot resolve these transients. Thus, observational progress in understanding lake drainage initiation will rely on field-based tools such as GPS networks and photogrammetry.

Kristin Poinar↗