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A number of models exist that attempt to explain wave imagery obtained with a synthetic aperture radar (SAR). These models are of two types; static models that depend on instantaneous surface features and dynamic models that employ surface velocities. Radar backscatter values (sigma_{0} ) were calculated from 1.3- and 9.4-GHz SAR data collected off Marineland, FL. Thesigma_{0} data (averaged over many wave trains) collected at Marineland can best be modeled by the Bragg-Rice-Phillips model which is based on roughness variation and the complex dielectric constant of oceans. This result suggests that capillaries on the surface of oceanic waves are the primary cause for the surface return observed by a SAR. Salinity and temperature of the sea at small and medium incidence angles produce little effect upon sea-surface reflection coefficients atX -band, for either of the linear polarizations. The authors' observation of moving ocean, imaged by the SAR and studied in the SAR optical correlator, support a theory that the ocean surface appears relatively stationary in the absence of currents. The reflecting surface is most likely moving slowly (i.e., capillaries) relative to the phase velocity of the large gravity waves. 相似文献
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O. H. Shemdin W. E. Brown Jr. F. G. Staudhammer R. Shuchman R. Rawson J. Zelenka D. B. Ross W. McLeish R. A. Berles 《Boundary-Layer Meteorology》1978,13(1-4):193-202
Some early results from an oceanographic experiment staged off Marineland, Florida, in December 1975 are presented, viz., intercomparisons between the X-band and L-band imagery obtained by the Environmental Research Institute of Michigan's (ERIM) dual-wavelength, dualpolarization multiplexed radar. This radar allows direct comparison since the images are produced simultaneously. The wave data obtained from the radar imagery are compared with surface measurements of waves obtained with a pitch- and-roll buoy. The conclusions are only applicable to medium and low wind and wave conditions encountered during the Marineland test. The results indicate that X-band images provide superior quality wave imagery and more useful Fourier Transforms compared to L-band under equivalent signal-to-noise ratios and resolution. Optimum wave imagery is seen when waves propagate in the range direction. Comparisons betweenin situ measurements and X-band imagery of the same area indicate that the dominant wave direction can be obtained from imagery to within a few degrees. A one-dimensional spectrum obtained from X-band imagery compares favorably with an equivalent wave frequency spectrum obtained from the pitch- and-roll buoy after suitable transformation asing linear wave theory. 相似文献
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The usual operation of a synthetic-aperture radar (SAR) assumes that the sensor platform moves at a constant velocity along a straight line and that objects to be imaged are stationary. Moving ocean waves perturb the Doppler frequencies in the SAR phase histories, and when processed in a conventional manner, they produce images of waves that are dispersed and thus defocused in the azimuth (along-track) direction. This defocusing can be compensated in the processor by readjusting the azimuth focus by an amount proportional to the velocity of the wave.The relationship among the parameters of the radar system, the SAR processor, and the relative target velocity is, theoretically determined for radars that operate at both X- and L-band frequencies. Experimental observations support these calculations. The effect of varying spectrum sampling, range focus, and number of coherent averages or looks is also observed. 相似文献
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Simultaneously obtainedX - andL -band synthetic aperture radar (SAR) data collected during the Marineland Experiment were spectrally analyzed by fast Fourier transform (FFT) techniques to estimate ocean wavelength and direction. An eight-sided flight pattern was flown over the same ocean area in order to study the sensitivity of the spectral estimate on radar look direction. These spectral estimates were compared with in situ wave measurements made by a pitch-and-roll buoy. The comparison revealed that theX -band SAR detected all gravity waves independent of radar look direction, while theL -band SAR detected all range-traveling gravity waves but failed to detect waves in three of four cases in which the waves were traveling within 25° of the azimuth direction. The analysis also indicates that azimuth-traveling waves appear longer and more range-traveling in the SAR imagery than observed by in situ instrumentation. It is postulated that degraded azimuth resolution due to scatterer motion is responsible for these observations. 相似文献
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