| WANG Yunhua,LIU Xiaoyan,LI Huimin,ZHANG Yanmin.Targets detecting in the ocean using the cross-polarized channels of fully polarimetric SAR data[J].Acta Oceanologica Sinica,2015,34(1):85-93 |
| 基于合成孔径雷达交叉极化通道数据的海上目标探测 |
| Targets detecting in the ocean using the cross-polarized channels of fully polarimetric SAR data |
| 投稿时间：2014-04-24 修订日期：2014-09-10 |
| DOI：10.1007/s13131-015-0601-3 |
| 中文关键词: 方位向模糊 极化合成孔径雷达 恒虚警率探测算法 |
| 英文关键词:azimuth ambiguities polarimetric SAR CFAR detection algorithm |
| 基金项目:The National Natural Science Foundation of China under contract Nos 41376179 and 41106153. |
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| 中文摘要: |
| 海上目标的方位向模糊(鬼影)在合成孔径雷达(SAR)图像中常被误检为真实目标, 从而引起虚警. 因此, 基于SAR图像的海上目标探测过程中, 方位向模糊目标的剔除技术引起了广泛关注. 基于互易性定理, 真实目标两交叉极化通道后向散射场的相位和振幅是相等的, 然而, 对于方位向一阶模糊目标而言, 两交叉极化通道数据却存在 ±π的相位偏移. 正是基于这一物理特性, 本文定义两交叉极化通道回波数据乘积的实部作为海上目标探测的一个新参数, 下文中该参数用A12r表示. 与其它参数相比较发现: 将A12r图像进行均值滤波, A12r图像中目标和海背景的对比度明显提高. 为了能应用恒虚警率算法探测A12r图像中的目标, 文中基于Wishart分布模型推导给出了海面回波 数据所满足的概率密度函数. 在A12r图像中, 因为方位向模糊目标的A12r值小于零, 而真实目标的A12r值大于零, 因此, 本文算法可完全剔除方位向模糊目标. 文中应用RAdARSAT-2全极化数据验证了所建算法的有效性. |
| 英文摘要: |
| Azimuth ambiguities (ghost targets) discrimination is of great interest with the development of a synthetic aperture radar (SAR). And the azimuth ambiguities are often mistaken as actual targets and cause false alarms. For actual targets, HV channel signals acquired by a fully polarimetric SAR are approximately equal to a VH channel in magnitude and phase, i.e., the reciprocity theorem applies, but shifted in phase about ±π for the first-order azimuth ambiguities. Exploiting this physical behavior, the real part of the product of the two cross-polarized channels, i.e. (SHVSVH*), hereafter called A12r, is employed as a new parameter for a target detection at sea. Compared with other parameters, the contrast of A12r image between a target and the surrounding sea surface will be obviously increased when A12r image is processed by mean filtering algorithm. Here, in order to detect target with constant false-alarm rates (CFARs), an analytical expression for the probability density function (pdf) of A12r is derived based on the complex Wishart-distribution. Because a value of A12r is greater/less than 0 for real target/its azimuth ambiguities, the first-order azimuth ambiguities can be completely removed by this A12r-based CFAR technology. Experiments accomplished over C-band RAdARSAT-2 fully polarimetric imageries confirm the validity. |
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