中文摘要：

Fourier衍射投影定理可用于水下目标重建和水声目标散射特性分析。将目标和周围介质的声学参数分布以二值图像描述,计算目标特性时需旋转目标图像而维持入射方向不变得到不同角度的投影。若直接用几何变换旋转二值图像,由于像素间的映射并非一一对应,会加重图像边缘的锯齿并在局部区域产生空值点。以极坐标系矩形网格下的平移实现目标旋转,再用形态学的开闭运算对重新变换到笛卡尔坐标系的图像边缘进行平滑,可有效提高旋转精度和速度,改善图像重建系统的性能。实验结果表明该方法有助于快速获取投影数据,提高目标重建系统的性能。

英文摘要：

In reconstructing acoustic object and predicting sound scattering based on the Fourier diffraction theorem,projections in all directions are calculated by rotating the object while maintaining the incident wave unchanged.Object rotation is time consuming,and suffers from errors due to ruggedness of the edges and holes inside the object caused by dicretization.To improve computation efficiency and quality of the rotated image,the discretized binary object in the Cartesian system is converted into polar coordinates and presented on rectangular grids.In this way,rotation of the object is achieved by translation in the rectangular grid-represented polar system,and the result is converted back to the Cartesian system.The obtained image is then smoothed with morphological opening and closing operations.The proposed method can significantly reduce the computational burden,avoid holes and reduce edge ruggedness,thus improve accuracy of the computed projections.