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  • 1
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    Preliminary results from the ASF/GPS ice classification algorithm (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The European Space Agency Remote Sensing Satellite (ERS-1) satellite carried a C-band synthetic aperture radar (SAR) to study the earth's polar regions. The radar returns from sea ice can be used to infer properties of ice, including ice type. An algorithm has been developed for the Alaska SAR facility (ASF)/Geophysical Processor System (GPS) to infer ice type from the SAR observations over sea ice and open water. The algorithm utilizes look-up tables containing expected backscatter values from various ice types. An analysis has been made of two overlapping strips with 14 SAR images. The backscatter values of specific ice regions were sampled to study the backscatter characteristics of the ice in time and space. Results show both stability of the backscatter values in time and a good separation of multiyear and first-year ice signals, verifying the approach used in the classification algorithm.
    Keywords: OCEANOGRAPHY
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 573-575.
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  • 2
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    Identification of sea ice types in spaceborne synthetic aperture radar data (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This study presents an approach for identification of sea ice types in spaceborne SAR image data. The unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look-up tables containing the expected backscatter signatures of different ice types measured by a land-based scatterometer. Extensive scatterometer observations and experience accumulated in field campaigns during the last 10 yr were used to construct these look-up tables. The classification approach, its expected performance, the dependence of this performance on radar system performance, and expected ice scattering characteristics are discussed. Results using both aircraft and simulated ERS-1 SAR data are presented and compared to limited field ice property measurements and coincident passive microwave imagery. The importance of an integrated postlaunch program for the validation and improvement of this approach is discussed.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; 2391-240
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  • 3
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    Ice tracking techniques, implementation, performance, and applications (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Present techniques of ice tracking make use both of cross-correlation and of edge tracking, the former being more successful in heavy pack ice, the latter being critical for the broken ice of the pack margins. Algorithms must assume some constraints on the spatial variations of displacements to eliminate fliers, but must avoid introducing any errors into the spatial statistics of the measured displacement field. We draw our illustrations from the implementation of an automated tracking system for kinematic analyses of ERS-1 and JERS-1 SAR imagery at the University of Alaska - the Alaska SAR Facility's Geophysical Processor System. Analyses of the ice kinematic data that might have some general interest to analysts of cloud-derived wind fields are the spatial structure of the fields, and the evaluation and variability of average deformation and its invariants: divergence, vorticity and shear. Many problems in sea ice dynamics and mechanics can be addressed with the kinematic data from SAR.
    Keywords: OCEANOGRAPHY
    Type: Advances in Space Research (ISSN 0273-1177); 12; 7; p. 141-147.
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  • 4
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    Wave propagation in the marginal ice zone - Model predictions and comparisons with buoy and synthetic aperture radar data (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The Labrador ice margin experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada in March 1987, provided aircraft SAR imagery, ice property and wave buoy data. Wave energy attenuation rates are estimated from SAR data and the ice motion package data that were deployed at the ice edge and into the ice pack, and compared with a model. It is shown that the model data comparisons are quite good for the ice conditions observed during LIMEX 1987.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 4605-462
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  • 5
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    Determination of sea ice motion using digital SAR imagery (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Precise, densely sampled maps of ice motion have been derived from digital Seasat SAR imagery, in order to determine the small scale spatial variability of ice formation. The SAR images were processed to remove geometric distortions, and then located to an accuracy of about 100 m by means of a spacecraft orbital data/SAR characteristics algorithm, independently of attitude and ground reference point data. Ice features common to an overlapping pair of images yielded vector plots of ice motion that indicate a high degree of spatial deformation, demonstrating the potential value of spaceborne SAR data.
    Keywords: OCEANOGRAPHY
    Type: IEEE Journal of Oceanic Engineering (ISSN 0364-9059); OE-10; 358-367
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  • 6
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    The age and source of ocean swell observed in Hurricane Josephine (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A simple kinematic model is applied to SIR-B observations in the far field of Hurricane Josephine in order to estimate the swell origin in space and time. The SIR data was obtained on October 12, 1984, and the geometry of the hurricane swell kinematic model is described. Estimates of the wavenumber and wave age and generation regions of the system are graphically presented and examined. The data reveal that the waves of Hurricane Josephine were generated 0-9 hours before the SIR-B overpass.
    Keywords: OCEANOGRAPHY
    Type: Johns Hopkins APL Technical Digest (ISSN 0270-5214); 8; 94-99
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  • 7
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    Wave evolution in the marginal ice zone - Model predictions and comparisons with on-site and remote data (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ocean-wave dispersion relation and viscous attenuation by a sea ice cover were studied for waves in the marginal ice zone (MIZ). The Labrador ice margin experiment (Limex), conducted off the east coast of Newfoundland, Canada in March 1987, provided aircraft SAR, wave buoy, and ice property data. Based on the wave number spectrum from SAR data, the concurrent wave frequency spectrum from ocean buoy data, and accelerometer data on the ice during Limex '87, the dispersion relation has been derived and compared with the model. Accelerometers were deployed at the ice edge and into the ice pack. Data from the accelerometers were used to estimate wave energy attenuation rates and compared with the model. The model-data comparisons are reasonably good for the ice conditions observed during Limex' 87.
    Keywords: OCEANOGRAPHY
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  • 8
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    Ice classification algorithm development and verification for the Alaska SAR Facility using aircraft imagery (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Alaska SAR Facility (ASF) at the University of Alaska, Fairbanks is a NASA program designed to receive, process, and archive SAR data from ERS-1 and to support investigations that will use this regional data. As part of ASF, specialized subsystems and algorithms to produce certain geophysical products from the SAR data are under development. Of particular interest are ice motion, ice classification, and ice concentration. This work focuses on the algorithm under development for ice classification, and the verification of the algorithm using C-band aircraft SAR imagery recently acquired over the Alaskan arctic.
    Keywords: OCEANOGRAPHY
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  • 9
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    Waves in frazil and pancake ice and their detection in Seasat synthetic aperture radar imagery (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements of wavelength and direction derived from SAR imagery obtained from Seasat in October 1987 are compared with a theoretical model of waves propagating into an ice cover composed of frazil and pancake ice. The dispersion relation for phase and group velocities is derived, and the existence of an upper frequency limit for propagation into the ice is found. The wave radiation pressure exerted on the ice is derived from the reflection coefficient at the ice edge; it is found to cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration. When the frazil ice becomes transformed into pancake ice, the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the Bragg wavelength. Directional wave number spectra are derived outside and inside the ice cover. The change of wavelength and angle of refraction of the dominant wave entering the ice field are both found to be characteristic of the dispersion relation derived theoretically.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 8835-885
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  • 10
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    Beaufort-Chukchi ice margin data from Seasat - Ice motion (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The motion of sea ice in the summer and fall marginal zone of the Beaufort and Chukchi seas is observed by tracking ice features in sequential Seasat synthetic aperture radar images. Four examples of ice motion fields are shown and discussed with translation observation density finer than one observation per 5 km for the most part. In this region the components of proportional relative motion are shown to commonly have values in the range 0.1 to 0.25/day throughout the marginal zone, which itself has a scale of the order of 100 km.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 7163-717
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