A Fast Algorithm for Establishing 3-D Scattering Center Model for Ship Targets over Sea Surface Using the Shooting and Bouncing Ray Technique
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摘要: 海面舰船目标3维散射中心的快速建模对雷达目标信号快速仿真、特征提取与分类识别等应用具有重要意义。该文结合目标-海面耦合散射的“4路径”模型、随机海面散射修正Fresnel反射系数模型,以及基于射线管积分的快速3维成像等模型与方法,提出一种舰船-海面复合的快速3维成像方法,并通过CLEAN算法建立一种3维散射中心快速建模算法。该算法由于实现了单频、单视角条件下的目标3维成像,并且采用简化的海面模型避免了大量海面面元的构建,因而大大提高了3维散射中心建模的计算效率,从而满足实际工程应用的需求。典型海面舰船目标仿真实验结果表明,与传统基于FFT的3维成像算法相比,在典型计算条件下该算法的计算效率可提高4个数量级。不同海情下,3维散射中心重建的与直接仿真计算的1维距离像历程图和2维像的对比结果,也验证了算法的计算精度。Abstract: Fast construction of the 3-D scattering centers of ship targets on the sea surface is important for many radar applications, including the fast signature prediction, feature extraction, and automatic recognition of targets. Combining the " four-path” model for target-surface coupling scattering with modified Fresnel reflection coefficient model in the stochastic sea surface and ray tube integration method, we propose a 3-D image formation method for ship-surface compound targets. Using the CLEAN technique on 3-D image, we develop a fast algorithm for establishing 3-D scattering center model for ship targets on the sea surface. Because this algorithm realizes 3D imaging of targets at a single frequency and single aspect angle, and adopts simplified surface model to avoid the need to construct a large number of surface elements, the computational efficiency of the proposed alogrithm is greatly increased to meet the needs of practical engineering applications. Simulation experiments of a typical ship target show that the proposed algorithm can increase the speed by four orders of magnitude under typical conditions, as compared with the traditional FFT-based 3D imaging method. We validate the accuracy of this algorithm by comparing reconstructed 1-D range profiles and ISAR images obtain by the scattering center model with the ones that are directly simulated.
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表 1 全方位(0°~360°)合成显示的3维散射中心模型及其重建的1维距离像历程图的重构度评估
Table 1. Display of synthesized 3D scattering center model at various azimuth (0°~360°) and comparison of sinograms calculated by direct simulation and rebuilt by the models
3维散射中心分布 仿真的1维距离像历程图 模型重建的1维距离像历程图 相似度(%) 89.55 表 2 不同海情下3维散射中心模型及其重建的2维ISAR像重构度评估(方位90°)
Table 2. Display of 3D scattering center models and comparison of ISAR images calculated by direct simulation and rebuilt by the models under different sea conditions at azimuth 90°
海情等级 3维散射中心分布 仿真的2维像 模型重建的2维像 相似度(%) 0级 89.66 1级 82.89 2级 81.75 3级 81.76 表 3 不同入射方位下3维散射中心模型及其重建的2维ISAR像重构度评估(1级海情)
Table 3. Display of 3D scattering center models and comparison of ISAR images calculated by direct simulation and rebuilt by the models at different azimuth under level-1 sea condition
方位角(°) 3维散射中心分布 仿真的2维像 模型重建的2维像 相似度(%) 30 79.11 60 79.89 120 86.25 150 86.23 表 4 3维散射中心计算效率对比(以用于计算3维散射中心的3维成像分辨率取0.1 m×0.1 m×0.1 m为例)
Table 4. Comparison of computation time by traditional algorithm and proposed algorithm (take the resolution 0.1 m×0.1 m×0.1 m in 3D images as example)
方法 模块 计算条件 计算时间(min) 总计 效率提高比 传统算法 SBR:计算扫频扫角RCS幅相数据 采样点个数:频率600,方位600,俯仰600 360000 360008 72000倍 3D-FFT:计算3维像 点数:2048 5 CLEAN:提取3维散射中心 动态范围:50 dB 3 本文算法 3D-RIM:直接计算3维像 采样点个数:频率1,方位1,俯仰1 2 5 CLEAN:提取3维散射中心 动态范围:50 dB 3 注: RIM表示射线积分方法(Ray-tube Integration Method) -
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