中文摘要：

水下目标散射回波在时域、频域混叠在一起，而且受声波入射角度的影响严重，在不同的入射角度下表现出很大的差异，需要建立全方位入射角度下回波分量的理论分析模型．本文推导了目标几何声散射分量在分数阶傅里叶变换域中随入射角度变化的解析表达式；确定了目标几何声散射回波分量在最佳分数阶傅里叶变换域中的全方位模型，从理论上证明了目标回波的几何特征形式；给出了离散分数阶傅里叶变换对声散射分量的分辨能力和计算精度与发射信号带宽和观测时间之间的关系．实验数据处理表明，建立的分数阶傅里叶变换域的全方位模型与目标几何特征是一致的，对未知入射角度下的目标识别提供了理论依据．

英文摘要：

The components of the underwater target scattering waves alias together in time domain and frequency domain realistically. They are affected by the incident angle, and show great differences under different angles. It is necessary to build an analytical model of scattering waves under all-direction incident angles theoretically. The analytical expressions of geometrical scattering components changing with the incident angle in fractional Fourier transform domain are deduced in this paper. The all-direction model in optimal fractional Fourier transform domain of the scattering waves is built. Based on this, the geometrical feature of underwater target echo is provided. In addition, the relationships between the resolution and the bandwidth of transmitted signal, and between the calculation accuracy and the length of observational signal are given. By processing experimental data, it is is in accordance with the characteristics of underwater under unknown incident angle. indicated that the model in fractional Fourier transform domain target. It can provide a theoretical basis for target recognition