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  • OCEANOGRAPHY  (3)
  • 1
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    The modulation of a radar signal from the ocean surface due to slope and hydrodynamic effects (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The modulation of the signal level of a tower-based radar scatterometer illuminating a small area of the ocean surface is predicted from direct measurements of the hydrodynamic conditions of the ocean surface and compared with X band radar measurements taken simultaneously. The radar backscatter is assumed to be due to Bragg resonance between the signal and the ripple waves. The effects of the slope of the ocean surface due to passing long waves are modeled by converting a measured wave height series into a slope time series. Laser-slope-gauge measurements of the spectrum of the ripple waves that ride upon the long ocean waves are used to predict the hydrodynamic effects. Comparisons with the measured radar signal show that the slope modulation alone gives a poor prediction of the modulation. Inclusion of the hydrodynamic effects in the simulation appears more promising, although it also is not entirely successful with this data set.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 16291-16
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    A video-aided study of sea spikes in radar backscatter at moderate incidence (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: Backscatter from a lake was measured at a 37-deg incidence angle using an FM-CW radar operating on X band and C band simultaneously. A limited amount of Ka-band data was also collected at 50 deg incidence. A video camera recorded the activity within the footprint looking upwind and crosswind. The video showed that breaking waves at all look directions and wedge-shaped waves when looking upwind consistently produced spikes in the radar time series. However, 62 percent to 90 percent of the spikes were not attributable to any surface structure visible on the video picture except wave crests. These spikes may be due to specular reflections or micro-scale breaking too small to be seen. Individual contributions to the backscattering coefficient were calculated for unattributed spikes, breaker spikes, and wedge spikes.
    Keywords: OCEANOGRAPHY
    Type: IGARSS ''91: Annual International Geoscience and Remote Sensing Symposium; Jun 03, 1991 - Jun 06, 1991; Espoo; Finland
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Synthetic-aperture-radar imaging of the ocean surface using the slightly-rough facet model and a full surface-wave spectrum (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A new model of synthetic-aperture-radar (SAR) imaging of ocean waves is described. The model is based on mapping individual, slightly-rough surface facets through the SAR processor into the image and responses of the facets in the image domain are added together coherently to give the composite image. A windowing technique allows both the orbital motion and the phase velocity of the long waves to be included. It is determined that the azimuthal cut-off is due to a smearing of the response of the facets in the image induced by the random orbital motion of the intermediate large-scale waves and that the focus adjustment that gives the greatest image contrast is half the phase velocity of the dominant long wave. The optimal processing technique, however, may consist of spatially offsetting the multiple looks on the image domain to compensate the propagation of long waves during the integration time of the SAR.
    Keywords: OCEANOGRAPHY
    Type: International Journal of Remote Sensing (ISSN 0143-1161); 11; 1451-148
    Format: text
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    NASA TECHNICAL REPORTS
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