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The Simulation of the SAR Image of a Ship Wake

1991
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Release : 1991
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Book Synopsis The Simulation of the SAR Image of a Ship Wake by :

Download or read book The Simulation of the SAR Image of a Ship Wake written by . This book was released on 1991. Available in PDF, EPUB and Kindle. Book excerpt: This paper describes a computer simulation of L-band synthetic aperture radar (SAR) images of surface-ship wakes and compares the simulation results to actual satellite-borne SAR imagery. The model used in the simulation accounts for both the disturbance produced in the water by the moving ship and the influence of the background sea. The radar scatter from the wake is modelled using the Bragg mechanism. A two-scale model of the sea surface is employed which assumes that the small-wavelength Bragg waves are modulated by the larger scale ambient sea & wake fluctuations. Several components of the wake are modelled: the ambient waves, the Kelvin wake, and the turbulent wake.

Near-Field Ship Wake Signature Modeling and Simulation

1994
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Release : 1994
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Book Synopsis Near-Field Ship Wake Signature Modeling and Simulation by : D. Lyzenga

Download or read book Near-Field Ship Wake Signature Modeling and Simulation written by D. Lyzenga. This book was released on 1994. Available in PDF, EPUB and Kindle. Book excerpt: A frequently observed characteristic of Synthetic Aperture Radar (SAR) imagery of moving ships is an area of increased backscatter immediately behind the ship extending approximately one ship length. The region causing these signatures has been termed the near-field disturbed water (NFDW) region of the ship. In this report a simple prediction model for these signatures is presented. This model utilizes a Fourier transform solution for the Kelvin wake along with a numerical procedure for calculating the hull pressure distribution. The model appears to predict the breaking regions more or less correctly for ship hulls having a rectangular stern, but over predicts the extent of the breaking regions for non-rectangular stern shapes. This limitation is apparently due to the fact that energy dissipation due to wave breaking has not been included. Outputs from the NFDW model are used to simulate a SAR image of the NFDW region and encouraging agreement between the appearance of the simulated and actual SAR images is found. The dependence of the NFDW with ship speed is in agreement with observations.

SAR (Synthetic Aperture Radar) Imaging of Ship Wakes in the Gulf of Alaska

1987
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Release : 1987
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Book Synopsis SAR (Synthetic Aperture Radar) Imaging of Ship Wakes in the Gulf of Alaska by : Omar H. Shemdin

Download or read book SAR (Synthetic Aperture Radar) Imaging of Ship Wakes in the Gulf of Alaska written by Omar H. Shemdin. This book was released on 1987. Available in PDF, EPUB and Kindle. Book excerpt: Conclusions include: 1.) The half-angles associated with narrow-V wakes are consistent with first-order Bragg surface theory. 2) The decay rate along the bright arms of the narrow-V wake is consistent with a combined viscous and radiation decay of short surface wave with first-order Bragg wave lengths. 3) Narrow-V wakes are observed in Sea States 1-3 at incidence angles less than or equal to 44 deg. The limitation is due to the noise threshold of the SAR system used. 4) The longest narrow-V wakes bright-arm observed is 12.0 km (31 deg. incidence angle) in Sea State 1, 3.9 km (44 deg incidence angle) in Sea State 2 and 4.3 km (24 deg incidence angle) in Sea State 3. In Sea State 4 no narrow-V wakes could be observed. 5) The turbulent wake (dark band between bright arms) is observed in Sea States 1-3 at incidence angles less than 53 deg. The limitations is due to the noise threshold in the SAR system used. 6) The longest turbulent wake length observed is 41 km (37 deg incidence angle) in Sea State 1, 4.5 km (35 deg incidence angle) in Sea State 2 and 5.5 km (24 deg incidence angle) in Sea State 3. No turbulent wake is observed in Sea State 4. Keywords: Synthetic aperture radar backscattering; Ocean surface waves; Deep mixed-layer marine environments; Deep water; Radar images.

Using Ship Wake Patterns to Evaluate Sar Ocean Wave Imaging Mechanisms

1985 Artificial satellites
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Release : 1985
Genre : Artificial satellites
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Book Synopsis Using Ship Wake Patterns to Evaluate Sar Ocean Wave Imaging Mechanisms by : R. R. Hammond

Download or read book Using Ship Wake Patterns to Evaluate Sar Ocean Wave Imaging Mechanisms written by R. R. Hammond. This book was released on 1985. Available in PDF, EPUB and Kindle. Book excerpt: The Joint Ocean Wave Investigation Project (JOWIP) was conducted to evaluate the detectability of ocean wave structures on imaging synthetic aperture radar (SAR). This project used Kelvin surface ship wake patterns generated under controlled and well documented surface environmental conditions to isolate SAR image parameters. Use of waves of known wavelength and direction provide the opportunity to evaluate the SAR contribution to ocean wave forecasting. SEASAT-like images made with L-band SAR are presented: (1) to suggest how ship-generated surface roughness combines with the velocity-bunching mechanism in calm ocean areas to produce the unusually narrow wakes observed for azimuth-traveling ships on SEASAT images; and (2) to estimate conditions under which SAR image modulation mechanisms can be expected to produce wake images. A method is described for using the Kelvin transverse ship wake wave component to quantitatively evaluate the contributions of various SAR ocean wave imaging mechanisms. It makes use of the narrow sector of surface roughness generated by a ship along its track to produce SAR images of the longest waves in its wake system on flat calm water.

SAR Detection of Ship-Generated Turbulent and Vortex Wakes

1985
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Release : 1985
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Book Synopsis SAR Detection of Ship-Generated Turbulent and Vortex Wakes by : J. D. Lyden

Download or read book SAR Detection of Ship-Generated Turbulent and Vortex Wakes written by J. D. Lyden. This book was released on 1985. Available in PDF, EPUB and Kindle. Book excerpt: A frequently observed ship wake feature in Synthetic Aperture Radar (SAR) images is a dark, narrow line along the ship track. These features have been termed turbulent wakes, although it is not clear that turbulence alone is responsible for their appearance. It has been suggested that vortices produced by the ship's hull may be responsible for the suppression of surface waves near the ship track and an enhancement of the waves near the edge of the smoothed area. The primary purpose of this study was to use a hydrodynamic model for ship-generated vortices as input to existing radar backscatter models, and to use this hybrid model to produce simulated SAR ship wake signatures for comparison with actual measurements. For the limited number of cases considered, the simulated wake signatures agreed closely to those observed in actual SAR data. Our results also indicated that the SAR signatures are related to the vortex currents under low wind conditions and to the strain rates associated with the ship-generated vortices under high winds. Additional studies included the radar resolution dependence of SAR ship wake features as well as examination of the Fourier transform of a ship wake image for information which could be used in an automatic detection algorithm. Keywords: Radar images; Radar/ship signatures; Optical radar; Surface waves perturbations.

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