Research On Key Technologies Of Target Detection,Estimation,and Wideband Tracking For Maritime Isar

Inverse synthetic aperture radar(ISAR)is available to search the surveillance sea surface under all-weather all-day conditions.The information and ISAR images of interesting marine targets could be obtained for feature extraction and identification,which will be of advantage to enhance the nation's coastal defense.In this dissertation,several key technics of sea clutter modeling,target detection and parameter estimation in sea clutter,and wideband tracking for maritime surveillance ISAR are investigated and analyzed thoroughly as follows:1.Typical models for the statistical amplitude of sea clutter are introduced and the estimations of distribution parameters are provided.The Gamma distribution is demonstrated to be promising to model the amplitude distribution of sea clutter based on experimental results.The estimated shape parameters are observed to be slowly varied within a relative small scale of range.To model the sea clutter amplitude with Gamma distribution is beneficial to understanding the sea surface scattering principle,and the categories of the typical sea clutter models are also enriched.In addition,this phenomenon motivates us to investigate the constant false alarm rate(CFAR)detector in Gamma-distributed sea clutter.2.Two CFAR detectors,namely the MLG-CFAR based on maximum likelihood estimation and WAI-CFAR based on weighted amplitude iteration,are proposed for Gamma-distributed background.Theoretical analysis shows that the derived estimator of the MLG-CFAR is an asymptotically efficient estimator of the mean power of the Gamma clutter.With a known shape parameter,the MLG-CFAR is demonstrated to maintain CFAR property with respect to the scale parameter of the Gamma distribution.Simulation results validate the superiority and generality of the MLG-CFAR in homogenous Gamma-distributed background.Given that the performances of false alarm control at clutter edges and target detection in the multiple-target condition with traditional CFAR detectors are required to be improved,the WAI-CFAR is proposed by combining the advantages of cell averaging class CFAR detectors and ordered statistic class CFAR detectors.The WAI-CFAR is demonstrated to maintain CFAR property with respect to the scale parameter in Gamma-distributed background with a known shape parameter.The superiority of the WAI-CFAR,which is applicable to different clutter scenarios with corresponding weighting factors,is investigated and verified by simulations.3.Accurate estimations of the target parameters,such as range,radial velocity,and azimuth,are usually operated after target detection and are essential for the following target tracking and continuous ISAR imaging.On the basis of the existing engineering scheme,the mathematical model for the estimations of target range and radial velocity are theoretically derived based on the adjacent-cell amplitude-comparison method,and several examples for parameter estimations are provided.Given that the linear frequency-modulated continuous wave(LFMCW)is usually utilized in practical maritime ISAR and the antenna often works in staring and scanning modes,however,the effects of range-Doppler coupling on the range estimation with LFMCW and the additional modulations on the amplitude and phase of radar returns should be considered.As cures,a generalized mathematical model of coherent integration is firstly established,and a high-precision estimation method is proposed to eliminate the impact of antenna rotation on parameter estimation.The complete scheme for parameter estimation in practical ISAR system are provided.4.The target of interest could be selected for ISAR imaging with the knowledge of target parameters.Real-time tracking of moving targets is the prerequisite for continuous imaging and is advantageous to increase the coherent integration time for a better cross-range resolution.To relieve the estimation fluctuation and poor robustness of the RAT method with a single snapshot,a modified range and azimuth tracking approach based on centroid algorithm(RATCA)with forgotten factor is then proposed.Both theoretical analysis and simulation results verify the effectiveness and robustness of RATCA in conditions of echo missing.5.The performances of the proposed methods in this dissertation are evaluate d and verified through a large number of field data and experimental results.Results show that the MLG-CFAR,the WAI-CFAR,the refined parameter estimation methods,and the RATCA method achieve excellent performances and great feasibilities in practical scenario.In concluding,the key technics of target detection,estimation,and wideband tracking for maritime surveillance ISAR are basically solved.The proposed schemes are promising to be useful for the designing of the radar system and the signal processing method.