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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Sea ice motions in the Central Arctic pack ice as inferred from AVHRR imagery

Synoptic observations of ice motion in the Arctic Basin are currently limited to those acquired by drifting buoys and, more recently, radar data from ERS-1. Buoys are not uniformly distributed throughout the Arctic, and SAR coverage is currently limited regionally and temporally due to the data volume, swath width, processing requirements, and power needs of the SAR. Additional ice-motion observations that can map ice responses simultaneously over large portions of the Arctic on daily to weekly time intervals are thus needed to augment the SAR and buoys data and to provide an intermediate-scale measure of ice drift suitable for climatological analyses and ice modeling. Principal objectives of this project were to: (1) demonstrate whether sufficient ice features and ice motion existed within the consolidated ice pack to permit motion tracking using AVHRR imagery; (2) determine the limits imposed on AVHRR mapping by cloud cover; and (3) test the applicability of AVHRR-derived motions in studies of ice-atmosphere interactions. Each of these main objectives was addressed. We conclude that AVHRR data, particularly when blended with other available observations, provide a valuable data set for studying sea ice processes. In a follow-on project, we are now extending this work to cover larger areas and to address science questions in more detail.

Emery, William↗
NASA NTRS2018

Arctic Ocean Primary Productivity: The Response of Marine Algae to Climate Warming and Sea Ice Decline

Highlights: 1. Satellite estimates of ocean primary productivity (i.e., the rate at which marine algae transform dissolved inorganic carbon into organic material) were higher in 2018 (relative to the 2003-17 mean) for three of the nine investigated regions (the Eurasian Arctic, Bering Sea, and Baffin Bay). 2. All regions continue to exhibit positive trends over the 2003-18 period, with the strongest trends for the Eurasian Arctic, Barents Sea, Greenland Sea, and North Atlantic. 3. The regional distribution of relatively high (low) chlorophyll-a concentrations can often be associated with a relatively early (late) breakup of sea ice cover.

Frey, K.E.↗
NASA NTRS1975

Beaufort sea ice zones by means of microwave imagery

An analysis of the aircraft microwave data obtained during the AIDJEX pilot experiment is presented and compared with a recent analysis of the microwave brightness temperatures measured in situ in the vicinity of the n main AIDJEX camp. The sea ice is divided into five distinct zones, the properties of each are discussed in detail.

Gloersen, P.↗
NASA NTRS1991

Observations of the late-summer to fall sea ice transition with the 14.6 GHz Seasat scatterometer

Seasat 14.6-GHz scatterometer data are used to investigate variations in the large area-averaged backscatter signature during the late summer to fall transition. The temporal evolution in the backscatter coefficient indicates general changes in the surface properties of the sea ice which are attributed to the seasonal cycle. Notable events in this typical cycle are the meltpond maximum, rapid drainage or disappearance of the meltponds, fall cooling and freeze-up, and ultimately snowfall. All are manifested in the signature record, and a simple empirical scattering model is used to infer the mean snow and ice properties and their temporal variation.

Drinkwater, Mark R.↗
NASA NTRS2005

Impacts of the Variability of Ice Types on the Decline of the Arctic Perennial Sea Ice Cover

The observed rapid decline in the Arctic perennial ice cover is one of the most remarkable signal of change in the Arctic region. Updated data now show an even higher rate of decline of 9.8% per decade than the previous report of 8.9% per decade mainly because of abnormally low values in the last 4 years. To gain insights into this decline, the variability of the second year ice, which is the relatively thin component of the perennial ice cover, and other ice types is studied. The perennial ice cover in the 1990s was observed to be highly variable which might have led to higher production of second year ice and may in part explain the observed ice thinning during the period and triggered further decline. The passive microwave signature of second year ice is also studied and results show that while the signature is different from that of the older multiyear ice, it is surprisingly more similar to that of first year ice. This in part explains why previous estimates of the area of multiyear ice during the winter period are considerably lower than the area of the perennial ice cover during the preceding summer. Four distinct clusters representing radiometrically different types have been identified using multi-channel cluster analysis of passive microwave data. Data from two of these clusters, postulated to come from second year and older multiyear ice regions are also shown to have average thicknesses of 2.4 and 4.1 m, respectively, indicating that the passive microwave data may contain some ice thickness information that can be utilized for mass balance studies. The yearly anomaly maps indicate high gains of first year ice cover in the Arctic during the last decade which means higher production of second year ice and fraction of this type in the declining perennial ice cover. While not the only cause, the rapid decline in the perennial ice cover is in part caused by the increasing fractional component of the thinner second year ice cover that is very vulnerable to total melt due to warming in the Arctic, especially in spring.

Comiso, Josefino C.↗
NASA NTRS1988

Modelling changes in the dielectric and scattering properties of young snow-covered sea ice at GHz frequencies

Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, Canada, were made during the winter of 1982. Detailed measurements of snow density and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 9 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar backscatter signatures of young sea ice. The results show that backscatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from SAR or SLAR images.

Drinkwater, Mark R.↗
NASA NTRS2007

Abrupt Decline in the Arctic Winter Sea Ice Cover

Maximum ice extents in the Arctic in 2005 and 2006 have been observed to be significantly lower (by about 6%) than the average of those of previous years starting in 1979. Since the winter maxima had been relatively stable with the trend being only about -1.5% per decade (compared to about -10% per decade for the perennial ice area), this is a significant development since signals from greenhouse warming are expected to be most prominent in winter. Negative ice anomalies are shown to be dominant in 2005 and 2006 especially in the Arctic basin and correlated with winds and surface temperature anomalies during the same period. Progressively increasing winter temperatures in the central Arctic starting in 1997 is observed with significantly higher rates of increase in 2005 and 2006. The Atlantic Oscillation (AO) indices correlate weakly with the sea ice and surface temperature anomaly data but may explain the recent shift in the perennial ice cover towards the western region. Results suggest that the trend in winter ice is finally in the process of catching up with that of the summer ice cover.

Comiso, Josefino C.↗
NASA NTRS1984

Matrix partitioning and EOF/principal component analysis of Antarctic Sea ice brightness temperatures

A field of measured anomalies of some physical variable relative to their time averages, is partitioned in either the space domain or the time domain. Eigenvectors and corresponding principal components of the smaller dimensioned covariance matrices associated with the partitioned data sets are calculated independently, then joined to approximate the eigenstructure of the larger covariance matrix associated with the unpartitioned data set. The accuracy of the approximation (fraction of the total variance in the field) and the magnitudes of the largest eigenvalues from the partitioned covariance matrices together determine the number of local EOF's and principal components to be joined by any particular level. The space-time distribution of Nimbus-5 ESMR sea ice measurement is analyzed.

Murray, C. W., Jr.↗
NASA NTRS1974

A theory of wave scatter from an inhomogeneous medium with a slightly rough boundary and its application to sea ice

An analytical theory of electromagnetic wave scattering from an inhomogeneous medium with a slightly rough boundary surface is formulated. The inhomogeneity in the medium is assumed to vary continuously in the vertical direction and to have a small random variation in the horizontal direction. The medium is assumed to consist of two layers. Maxwell's equations are solved by using the small perturbation method together with Fourier transform technique. The resulting differential equations are solved by using WKB and variation of parameter methods. Field amplitudes in each medium are determined by taking boundary conditions into account. The expressions for first order polarized radar backscatter cross-section are obtained. An attempt is made to apply the developed theory to compute sea ice scatter. Numerical calculations are performed for polarized radar backscatter cross-section at two frequencies, 13.3 GHz and 400 MHz. It is shown that WKB method is applicable at both of these frequencies. Theoretical results are compared with the experimental results obtained from NASA Earth Resources Program mission 126. Theoretical results and experimental results are in good agreement.

Parashar, S. K.↗
NASA NTRS1984

Passive microwave characteristics of the Bering Sea ice cover during Marginal Ice Zone Experiment (MIZEX) West

Passive microwave measurements of the Bering Sea were made with the NASA CV-990 airborne laboratory during February. Microwave data were obtained with imaging and dual-polarized, fixed-beam radiometers in a range of frequencies from 10 to 183 GHz. The high resolution imagery at 92 GHz provides a particularly good description of the marginal ice zone delineating regions of open water, ice compactness, and ice-edge structure. Analysis of the fixed-beam data shows that spectral differences increase with a decrease in ice thickness. Polarization at 18 and 37 GHz distinguishes among new, young, and first-year sea ice types.

Cavalieri, D. J.↗
NASA NTRS1990

Mapping sea ice leads with a coupled numeric/symbolic system

A method is presented which facilitates the detection and delineation of leads with single-channel Landsat data by coupling numeric and symbolic procedures. The procedure consists of three steps: (1) using the dynamic threshold method, an image is mapped to a lead/no lead binary image; (2) the likelihood of fragments to be real leads is examined with a set of numeric rules; and (3) pairs of objects are examined geometrically and merged where possible. The processing ends when all fragments are merged and statistical characteristics are determined, and a map of valid lead objects are left which summarizes useful physical in the lead complexes. Direct implementation of domain knowledge and rapid prototyping are two benefits of the rule-based system. The approach is found to be more successfully applied to mid- and high-level processing, and the system can retrieve statistics about sea-ice leads as well as detect the leads.

Key, J.↗
NASA NTRS1973

Sea ice and surface water circulation, Alaskan Continental Shelf

The author has identified the following significant results. The boundaries of land-fast ice, distribution of pack ice, and major polynya were studied in the vicinity of the Bering Strait. Movement of pack ice during 24 hours was determined by plotting the distinctly identifiable ice floes on ERTS-1 imagery obtained from two consecutive passes. Considerably large shallow area along the western Seward Peninsula just north of the Bering Strait is covered by land fast ice. This ice hinders the movement of ice formed in eastern Chukchi Sea southward through the Bering Strait. The movement of ice along the Russian coast is relatively faster. Plotting of some of the ice floes indicated movement of ice in excess of 30 km in and south of the Bering Strait between 6 and 7 March, 1973. North of the Bering Strait the movement approached 18 km. The movement of ice observed during March 6 and 7 considerably altered the distribution and extent of polynya. These features when continually plotted should be of considerable aid in navigation of ice breakers. The movement of ice will also help delineate the migration and distribution of sea mammals.

Wright, F. F.↗
NASA NTRS1987

Variations of mesoscale and large-scale sea ice morphology in the 1984 Marginal Ice Zone Experiment as observed by microwave remote sensing

The data acquired during the summer 1984 Marginal Ice Zone Experiment in the Fram Strait-Greenland Sea marginal ice zone, using airborne active and passive microwave sensors and the Nimbus 7 SMMR, were analyzed to compile a sequential description of the mesoscale and large-scale ice morphology variations during the period of June 6 - July 16, 1984. Throughout the experiment, the long ice edge between northwest Svalbard and central Greenland meandered; eddies were repeatedly formed, moved, and disappeared but the ice edge remained within a 100-km-wide zone. The ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200-km-wide zone. The high-resolution ice concentration distributions obtained in the aircraft images agree well with the low-resolution distributions of SMMR images.

Campbell, W. J.↗