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The Research on Ship Imaging Algorithm under the Sea Clutter Background

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Tutor: JiangYiCheng
School: Harbin Institute of Technology
Course: Information and Communication Engineering
Keywords: inverse synthetic aperture radar,ship imaging,time-frequency analysis,sea clutte
CLC: TN958
Type: Master's thesis
Year:  2008
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Inverse synthetic aperture radar (ISAR) can acquire high resolution images of non-cooperative moving targets, such as the aircrafts and ships. It is very important for national defence. Because of the complex changes in attitude of ships and sea clutter¡¯s influence, the difficulty in achieving high quality images increases. In this paper, we have a deep study on the imaging of ship targets, investigate the signal model, imaging algorithm, simulation of the sea clutter and its suppressing algorithm.Firstly, we introduce the research status of radar imaging and sea clutter home and abroad, and then discuss the main theories of ISAR imaging. Many basic issues related to ISAR imaging are analyzed.According to movement complexity of ships, we obtain the signal model, discuss the characteristics of received signals while one or more dimentional rotation exists, and give the corresponding imaging simulation. When low conditions of the sea level, the ship 3-D rotation is very small, RD algorithm can be objective. However, when sea level is high, three-dimentional, rotation is obvious; this results in the variation of Doppler frequency of scatters. On this condition, instantaneous imaging is needed. In this paper, we select several time-frequency methods, analyze and compare their performance, and then give the corresponding instantaneous imaging results.Sea clutter is an important factor which affects the ship imaging.In the paper, we analyze the characteristics of sea clutter and model the K-distributed on the special condition of ship imaging, and then simulate the clutter with two methods, contraposing their shortage, a new method for modeling and simulation of correlated coherent K-distributed clutter is presented.In actual imaging situation , the clutter has two-dimensional time-space correlation, then we study the sea clutter of time-space correlation and simulate the two-dimensional time-space related sea clutter.According to different circumstances that the clutter and objectives of the echoes may be of, we analyze the sea clutter¡¯s influence.When signal and clutter Doppler frequency is not in case-aliasing, a approach in the Doppler domain separation is presented, and of the mixing situation, we can estimate the power spectrum of clutter, white the echo signals, and then use CFAR detection method. This can effectively suppresses the clutter¡¯s effect, and improves the imaging quality.
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