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Modeling of Sea Clutter and Effect of Sea Clutter on Isar Imaging

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Tutor: SuFuLin
School: Harbin Institute of Technology
Course: Information and Communication Engineering
Keywords: Inverse Synthetic Aperture Radar,Ship targets,Sea Clutter,K-Distribution
CLC: TN957.54
Type: Master's thesis
Year:  2008
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Inverse Synthetic Aperture Radar (ISAR) is a kind of high-resolution imaging radar,which can provide an all-weather and day/night capability to generate a high-resolution two-dimensional radar images of the targets over a long range. When ISAR generates images for targets on the sea, sea clutter may influence the imaging performance. This paper hereby establishes sea clutter model and analyzes the effect of sea clutter on ISAR imaging.Firstly, target imaging algorithm is studied. This paper builds geometric model of ship and analyzes the characteristics of ship motion. Then according to rotation matrix theory, the locations of ship’s scatters are derived at any time. Furthermore, this paper describes fundamental principle of ISAR imaging and motion compensation. Simulation includes different conditions with different motion at different time.Secondly, the amplitude distribution model of sea clutter and correlated characteristics are discussed. The model for describing amplitude characteristics of sea clutter is given by a K-distribution model. The K-distribution amplitude distribution model has a good explanation to the scattering mechanism of radar sea clutter and coincides with experimental data. Furthermore, the prediction for shape parameter and scale parameter of the K-distribution are given and how radar parameters, environment parameters and geometry parameters influencing shape parameter and scale parameter are describedThen, the methods of modeling and simulation for K-distributed sea clutter are studied. The simulation model of temporal correlated noncoherent K-distributed clutter is realized using Zero Memory Nonlinear(ZMNL) transform and the temporal correlated coherent K-distributed clutter’s is realized using Spherically Invariant Random Processes (SIRP), the validity of the methods are proved by simulated results. According to temporal correlation and spatial correlation, the simulation model of temporal-spatial correlated coherent K-distributed clutter is estimated using SIRP, because the sea clutter is two-dimensional in ISAR signal. Finally, this paper analyzes the effect of sea clutter on ISAR imaging and motion compensation. The effect of shape parameter on sea clutter which is simulated according to the model of temporal-spatial correlated coherent K-distributed sea clutter and the method of parameter prediction is discussed. Then add simulation sea clutter to target signal. Motion compensation is usually divided into two steps: range alignment and phase compensation. This paper only studies the effects of sea clutter on range alignment from range estimation error and cross correlation function, because phase compensation is used after range alignment. The effect of sea clutter is presented by simulation results. After ideal motion compensation, sea clutter would be a band interference in ISAR imaging, which will degrade imaging performance.
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