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摘要: 该文从全极化体制角度出发,提出一种基于极化联合特征的海面目标检测方法。首先基于极化协方差矩阵,通过Cloude特征分解,提取表征回波随机程度的极化熵和反熵的数学期望;接着直接基于极化散射矩阵,通过Krogager特征分解,提取表征回波中极化散射分量结构组成的球散射体分量、二面角散射体分量和螺旋体散射分量的归一化系数;由提取的特征构成五维特征空间,利用主成分分析(PCA)降维证明所提特征具有良好的可分性,最后采用一类支持向量机(OCSVM)对目标和杂波进行识别。所提方法分别从极化相干和非相干分解两个角度出发,通过两种不同的极化分解方式提取特征,在一定程度上解决了高海情下基于单一极化分解方法存在的检测效果不理想的问题。通过IPIX实测数据验证所提方法具有良好的检测能力。Abstract: Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. This paper proposes a method for detecting small targets on the sea surface based on the combination of polarization features of two models. The scattering mechanism of sea clutter is random scattering at low glazing angle or glancing angle and the randomness is high as the angles do not have any specified shape. However, a target has a specific shape, and thus, the randomness of scattering will be less. Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars. Such echoes typically return from ground, sea, rain, and animals/insects. In this literature, the randomness of a scattering mechanism in an echo is obtained from the probability density functions of polarization entropy using the Cloude decomposition model. Further, the proportion of scattering at spherical, dihedral, and helicoid angles from the target echoes will be different in the sea clutter. Therefore, the relative coefficient of power of these three scattering components in each echo is extracted based on Krogager polarization decomposition. Then, polarization features with good separability and complementarity are selected to form the polarization feature vector, and the characteristics are verified by Principle Component Analysis (PCA). Finally, One Class Support Vector Machine (OCSVM) is used for classification and recognition based on the polarization decomposition feature vector. Instead of single-polarization detection methods, our method uses two polarization modes to extract the decomposition features with separability and complementarity through polarization coherent decomposition and incoherent decomposition, respectively. The experimental results of the IPIX data show the effectiveness of our method. Thus, the detection performance of our model is better than those methods based on single-polarization decomposition in complex and difficult sea conditions.
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表 1 1993年IPIX雷达数据主要参数说明
Table 1. The description of IPIX datasets in 1993
序号 数据编号 目标所在单元 受目标影响单元 风速(km/h) 浪高(m) 平均信杂比(dB) 1 #17 9 8:11 9 2.2 11.95 2 #26 7 6:8 9 1.1 6.43 3 #30 7 6:8 19 0.9 2.96 4 #31 7 6:9 19 0.9 8.03 5 #40 7 5:8 9 1.0 11.39 6 #54 8 7:10 20 0.7 13.88 7 #280 8 7:10 10 1.6 6.20 8 #310 7 6:9 33 0.9 2.52 9 #311 7 6:9 33 0.9 11.38 10 #320 7 6:9 28 0.9 10.64 表 2 实验样本数说明
Table 2. The description of experimental sample number
观测时间(ms) 纯杂波样本数 目标样本数 训练样本数 测试样本数 纯杂波样本 纯杂波样本 目标样本数 128 10240 1024 5120 5120 1024 256 5120 512 2560 2560 512 512 2560 256 1280 1280 256 1024 1280 128 640 640 128 2048 640 64 320 320 64 4096 320 32 160 160 32 表 3 不同核函数下OCSVM在3组数据集上的检测正确率(%)
Table 3. The detection accuracy of OCSVM in the three datasets with different kernel functions
核函数类型 线性核函数 多项式核函数 Sigmoid核函数 高斯核函数 #54 50.49 91.91 74.51 96.81 #280 61.76 72.79 70.10 89.07 #311 33.82 86.27 76.72 95.10 表 4 不同极化分解后的检测性能
Table 4. The detection performance after different polarization decomposition
数据编号 特征向量 目标检测概率(%) 虚警概率(%) #280 $\left[ {{G_H},{G_A}} \right]$ 65.63 18.75 $\left[ {{K_s},{K_d},{K_h}} \right]$ 90.19 2.38 $\left[ {{G_H},{G_A},{K_s},{K_d},{K_h}} \right]$ 91.02 2.19 #311 $\left[ {{G_H},{G_A}} \right]$ 82.81 7.81 $\left[ {{K_s},{K_d},{K_h}} \right]$ 96.88 2.38 $\left[ {{G_H},{G_A},{K_s},{K_d},{K_h}} \right]$ 97.79 1.72 #320 $\left[ {{G_H},{G_A}} \right]$ 25.00 18.74 $\left[ {{K_s},{K_d},{K_h}} \right]$ 95.94 1.56 $\left[ {{G_H},{G_A},{K_s},{K_d},{K_h}} \right]$ 98.57 1.25 #54 $\left[ {{G_H},{G_A}} \right]$ 86.88 4.69 $\left[ {{K_s},{K_d},{K_h}} \right]$ 95.94 2.38 $\left[ {{G_H},{G_A},{K_s},{K_d},{K_h}} \right]$ 98.31 1.88 表 5 不同观测时间下不同方法的检测性能
Table 5. The detection performance of different methods in different observation time
观测时间(ms) ${C_R}$ ${F_R}$ DBEA Tri-FPC 3D-PFM 所提方法 DBEA Tri-FPC 3D-PFM 所提方法 128 0.8478 0.8961 0.8948 0.9126 0.0104 0.0104 0.0112 0.0126 1024 0.8596 0.9178 0.9197 0.9377 0.0107 0.0146 0.0137 0.0166 4096 0.8797 0.9510 0.9493 0.9668 0.0193 0.0175 0.0218 0.0181 -
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