Study Of Detection Algorithm For Weak Target Embedded In Sea Clutter

Sea clutter is the backscatter of radar electromagnetic waves from the rough sea surface. Features of sea clutter is influenced by combined factors of both environment of sea surface and radar system parameters. Sea clutter has strong energy, and is complex and non-stationary within time and space. When radar trys to dectect targets near sea surface, sea clutter comes in to the antenna and radar receiver along with target returns. Specially, when energy of target return is smaller or equal to sea clutter, radar detection for targets is severally interferred by sea clutter. These targets are weak targets embedded in sea clutter.Radar detection of weak targets is very important for navigation safety, disaster rescue, coastal management and homeland security, so it is payed more and more attention. In recent decades, researchers made a series of meaningful progress by a wide range of signal processing methods around this problem. However, there are still a lot of imperfections and unresolved difficulties, which need to explore and research. This paper starts the study based on the measured data from shore-based radar microwave radar platform and foreign public databases.This paper introduces the basic principles of radar target detection, including the basic structure of the radar system, radar range equation and the basic principles of radar detection. And then, the MORSE radar systems and measured radar data which is subsequently used are introduced and explained in detail.Based on the study of the physical mechanism of sea clutter from microwave radar working at low grazing angle, amplitude distribution characteristic of sea clutter is analyzed making use of common probability density function, and the measured data is fitted by these models. Then, Doppler spectrum of sea clutter is mathematically modeled and simulated. Finally, the fractal and multi-fractal theory are studied, and the multifractal detrended fluctuation analysis (MFDFA) method is utilized to analyze the measured data of sea clutter, indicating that real sea clutter data series is multifractal.According to the morphological characteristics of sea clutter Doppler spectrum, this paper proposed a median operator-based adaptive clutter suppression filter (MACSF). Numerical simulation and measured data are both used to validate the effectiveness of the method. Compared to the block adaptive clutter suppression filter (BACSF), MACSF well tracks the change of sea clutter in time and space, so the estimation of sea clutter power is more accurate. Moreover, the number of pulses needed for one processing interval is not very larger, so the method is suitable for real time processing.On the basis of sea clutter multifractal analysis, this paper proposes a target detection algorithm based on high order Hurst exponent. The algorithm makes use of the difference of the generalized Hurst exponent between echoes from targets and sea surface. Analysis of numerical simulation and the C-band and X-band radar data, show that the proposed method is able to detect slow or stationary targets in sea clutter, and the performance is better than existing box dimension-based dectection algorithm.In addition, this paper firstly apply the spectral kurtosis (SK) method to the problem of weak target detection in sea clutter. The algorithm steps and effect are analyzed by S-band radar data. Detection performance of the method are analyzed by the way of numerical simulation. The result shows that the proposed method is effective for moving targets in ordinary sea condition, while its performance declines for slow or stationary targets.Finally, this paper proposed four target detection schemes based on analysis of sea clutter and discussion of sea clutter suppression method and target detection method. These schemes are implemented for detection problem of moving and slow targets in sea clutter. The schemes are applied to different measured data to analyze the overall detection performance. These measured data are from S-band, C-cand and X-band radar respectively. And measured data from different sea conditions are available.