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  • 1
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    Synthetic aperture radar imaging of ocean waves - Comparison with wave measurements (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Synthetic aperture radar images of ocean waves were obtained in conjunction with reference wave data near Marineland, Florida, December 14, 1975. Each of the various types of measurements were processed into a form that allowed direct comparisons with the others. Maxima of radar spectra occurred at the same frequencies as the maxima of reference wave height spectra. In a comparison of a radar spectrum with observed spectra of wave height, wave orbital velocity, and surface slope the high-frequency portion of the radar spectrum lay near and between the wave height and the orbital velocity spectra but differed significantly from the surface slope spectrum. The radar-derived mean directions and model-fitted directional spreads of wave energy were close to the values from a directional wave buoy and indicated the accuracy of radar measurements of wave direction. However, a directional plot of a radar spectrum near shore at the frequency of the maximum showed a sharper peak than such a plot of a fitted spectrum derived from reference data.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research; 85; Sept. 20
    Format: text
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  • 2
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    Comparison of in situ and remotely sensed ocean waves off Marineland, Florida (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Comparison between X-band and L-band radar imagery of sea waves is made. Sea truth was obtained by in situ pitch-and-roll buoy measurements. Under the low wind and wave conditions of the tests, superior wave imagery and more useful Fourier transforms were obtained with X-band SAR as compared to L-band with equivalent signal-to-noise ratio and synthetic aperture resolution. A comparison between X-band wave images and the in situ measurements shows agreement in the dominant wave direction to within a few degrees. The normalized spectra show a striking resemblance in spectral shape.
    Keywords: OCEANOGRAPHY
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  • 3
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    Seasat synthetic aperture radar observations of wave-current and wave-topographic interactions (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This study investigated the capability of a spaceborne, imaging radar system to detect subtle changes in the propagation characteristics of ocean wave systems. Specifically, an evolving surface gravity wave system emanating from Hurricane Ella and propagating toward Cape Hatteras, NC, formed the basis of this investigation. This wave system was successfully imaged by the Seasat synthetic aperture radar (SAR) during revolution 974 on September 3, 1978. Estimates of the dominant wavelength and direction of the ocean waves were derived from the SAR data by using optical Fourier transforms. Environmental data of the test area, which included the surface velocity vector within the Gulf Stream, the location of Hurricane Ella, and local bathymetric information, were used in conjunction with the SAR data to form the basis of this comparative study. Favorable agreement was found between wave rays calculated by utilizing theoretical wave-current and wave-topographic interactions and SAR observed dominant wavelength and direction changes across the Gulf Stream and continental shelf.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; May 20
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  • 4
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    Synthetic aperture radar imaging of ocean waves during the Marineland experiment (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Wave contrast measurements are used to analyze X and L-band simultaneously obtained synthetic aperture radar (SAR) data of ocean gravity waves collected during the Marineland Experiment (1975). The results of the wave contrast measurements show that the ocean waves imaged by a SAR are more discernible using an X-band frequency than an L-band frequency and when the ocean waves are traveling in the range direction. It is determined that ocean waves can be detected by both X and L-band SAR, provided that the radar surface resolution is a small compared to the ocean wavelength. In addition, wave detection using L-band SAR can be improved by adjusting the focal distance and rotation of the cylindrical telescope in the SAR optical processor to account for wave motion. This adjustment is determined to be proportional to a value that is near the wave phase velocity.
    Keywords: OCEANOGRAPHY
    Type: IEEE Journal of Oceanic Engineering; OE-8; Apr. 198
    Format: text
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  • 5
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    Modeling of SAR signatures of shallow water ocean topography (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A hydrodynamic/electromagnetic model was developed to explain and quantify the relationship between the SEASAT synthetic aperture radar (SAR) observed signatures and the bottom topography of the ocean in the English Channel region of the North Sea. The model uses environmental data and radar system parameters as inputs and predicts SAR-observed backscatter changes over topographic changes in the ocean floor. The model results compare favorably with the actual SEASAT SAR observed backscatter values. The developed model is valid for only relatively shallow water areas (i.e., less than 50 meters in depth) and suggests that for bottom features to be visible on SAR imagery, a moderate to high velocity current and a moderate wind must be present.
    Keywords: OCEANOGRAPHY
    Type: NASA. Marshall Space Flight Center Frontiers of Remote Sensing of the Oceans and Troposphere from Air and Space Platforms; p 415-430
    Format: application/pdf
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  • 6
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    Interpretation of synthetic aperture radar measurements of ocean currents (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Synthetic Aperture Radar (SAR) experiments have been performed over the last few years to measure ocean currents inferred from shifts in the Doppler spectral peak. Interpretations of aircraft SAR measurements, when compared with limited surface values, tend to underestimate the currents by about 25%. A theory is developed that modifies the classical Doppler expression showing that the radar measurements are dependent on the radar processor (system) bandwidth and the received signal bandwidth. Measured bandwidths give a correction that increases the inferred current values by about 25%, bringing the measurements into good agreement. This new correction lends credence to the theory and increases the potential for application of SAR systems to future ocean current measurements. SAR measurements should include the determination of processor and signal bandwidths such that this correction can be applied.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research; 88; Feb. 28
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  • 7
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    Refraction of coastal ocean waves (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.
    Keywords: OCEANOGRAPHY
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  • 8
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    Synthetic aperture radar measurements of ocean surface currents (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: OCEANOGRAPHY
    Type: Geophysical Research Letters; 9; July 198
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  • 9
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    SAR imaging of waves in water and ice - Evidence for velocity bunching (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Synthetic aperture radar (SAR) images collected over the Arctic marginal ice zone show gravity wave patterns in both the open water and the ice. Diffuse wave patterns are visible in the water at near range (small incidence angles), while most distinct wave patterns are visible in the ice across the entire swath. The wave patterns in the ice appear as bright lines rather than sinusoidal intensity variations. Additionally, the images show a periodic displacement of the ice/water boundary, apparently due to Doppler shift effects associated with the gravity wave orbital motions. These observations are interpreted as evidence for the velocity bunching effect and also illustrate the effects of random scatterer motions in the open water.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 1031-103
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  • 10
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    The contribution of wedge scattering to the radar cross section of the ocean surface (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This letter considers the contribution to the radar cross section of the ocean surface due to scattering from edges for which the local radius of curvature is small compared with the radar wavelength. An analytic expression based on the method of equivalent currents is given for such scattering and is evaluated for several assumed sets of parameters. This contribution is shown to augment the Bragg scattering cross section in regions where the latter underestimates the measured radar cross section, while remaining smaller than the Bragg component elsewhere.
    Keywords: OCEANOGRAPHY
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-21; 502-505
    Format: text
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