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Motion Compensation and 3-D Imaging Algorithm in Sparse Flight Based Airborne Array SAR
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摘要: 该文针对机载交轨阵列SAR下视3维成像模型，采用以巴克码伪随机序列为准则的稀疏重航过采样方式，利用较少飞行次数提高交轨向分辨率。针对重航过采样方式存在的运动误差，利用修正均匀冗余阵列(Modified Uniformly Redundant Arrays, MURA)编码空间调制和3维后向投影(Back Projection, BP)算法获得各航过3维复图像对，基于干涉处理和频域压缩感知(Compressed Sensing, CS)等效实现各航过阵列形变误差补偿。将MURA反码对应回波形成的3维复图像相位作为参考，对各单航过复图像进行相位补偿，以恢复各航过间复图像相位关系。根据单航过阵列SAR3维复图像具备频域稀疏的性质，对各个复图像相干累加，实现稀疏重航过阵列SAR高分辨率下视3维成像。仿真和暗室试验数据处理结果验证了方法的有效性。Abstract: In this study, we adopt a criterion of Barker code to generate a high-resolution image from sparse flight samples to establish a three-dimensional (3-D) imaging model of airborne array SAR. Under the condition of motion error, we utilize the Modified Uniformly Redundant Arrays (MURA) modulation and 3-D Back Projection (BP) algorithm to obtain 3-D complex image pairs under each flight. Based on interferometry and Compressed Sensing (CS) in frequency domain, the array deformation error compensation is realized. The phases of 3-D complex image formed by the echo corresponding to negative MURA modulation are referred to perform phase compensation on each single-pass complex image to restore the image phase relation of each flight. Coherent accumulation of each complex image is implemented to realize high-resolution 3-D imaging under sparse flight sampling. Simulation analysis and experimental data verify the feasibility of the proposed method.
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图 1 机载稀疏重航过阵列SAR下视3维成像模型
Figure 1. Geometry of airborne downward-looking 3-D imaging SAR based on sparse flight
图 3 127×127大小MURA 2维编码及其自相关函数示意图
Figure 3. Code pattern and autocorrelation diagram of MURA with size of 127×127
图 4 稀疏重航过阵列SAR运动误差补偿和3维成像方法流程图
Figure 4. Signal processing chart of motion compensation and 3-D imaging algorithm in sparse flight based airborne array SAR
图 5 运动误差条件下航迹顺轨向-交轨向分布示意图
Figure 5. The sampling plane distribution of flight path under motion error
图 6 运动误差条件下各航迹顺轨向-高程向分布示意图
Figure 6. The along-track and range distribution of flight path under motion error
图 7 运动误差条件下位置测量误差引起的阵列形变斜距误差示意图
Figure 7. The range offset caused by array deformation error
图 8 理想飞行条件下单航过阵列SAR 3维成像结果
Figure 8. 3-D imaging results of single flight array SAR under ideal condition
图 9 理想飞行条件下7次未稀疏重航过阵列SAR 3维成像结果
Figure 9. 3-D imaging results with 7 flights array SAR under ideal condition
图 10 理想飞行条件下稀疏重航过阵列SAR 3维成像结果
Figure 10. 3-D imaging results of sparse flight array SAR under ideal condition
图 11 存在运动误差条件下7次重航过阵列SAR下视3维成像结果
Figure 11. Downward-looking 3-D SAR imaging results with 7 flights under motion error
图 12 阵列形变误差补偿前后对应的单航过SAR复图像频谱
Figure 12. SAR image spectrum of single flight before/after array deforming error compensation
图 13 运动误差条件下稀疏重航过阵列SAR运动误差补偿和3维成像结果
Figure 13. 3-D imaging results with sparse flights under motion error compensation
图 14 暗室试验观测场景和测试现场
Figure 14. The observed field and testing site in microwave anechoic chamber
表 1 机载交轨向稀疏重航过阵列SAR仿真参数
Table 1. Simulation parameters of airborne sparse flight array SAR
参数 数值 参数 数值 飞行高度 2000 m 顺轨向天线子阵尺寸 1.0 m 信号带宽 300 MHz 交轨向阵列天线长度 9 m 雷达工作波长 0.03 m 各航过飞行间隔 9.15 m 脉冲重复频率 400 Hz 顺轨向分辨率 0.50 m 载机飞行速度 75 m/s 高程向分辨率 0.5 m 交轨向等效相位中心数量 61 单航过交轨分辨率 3.33 m 交轨向等效相位中心间隔 0.15 m 7次重航过交轨分辨率 0.47 m 交轨向幅宽 200 m 稀疏重航过交轨分辨率 0.55 m 
下载: 导出CSV
表 2 运动误差条件下的3维成像结果误差分析
Table 2. 3-D imaging performance analysis under motion error
成像方法 相关系数 RMSE(m) SSIM 理想条件单航过阵列SAR 3维BP成像 0.7378 0.1083 0.7936 理想条件未稀疏重航过阵列SAR 3维BP成像 0.9216 0.0111 0.9532 理想条件巴克码稀疏重航过阵列SAR 3维BP成像 0.8718 0.0146 0.9079 运动误差下巴克码稀疏重航过阵列SAR 3维BP成像 0.8205 0.0276 0.8908 运动误差下巴克码稀疏重航过阵列SAR运动误差补偿和3维成像 0.8904 0.0151 0.9312
下载: 导出CSV
表 3 试验参数
Table 3. Experimental parameters
参数 数值 参数 数值 测试距离R0 1.60 m 顺轨向采样点数 51 雷达工作波长 $\lambda$ 0.03 m 高程向采样点数 201 信号总带宽B 4 GHz 交轨向分辨率 0.027 m 天线扫描面大小 1.00 m×1.00 m 顺轨向分辨率 0.027 m 交轨向采样点数 51 高程向全带宽分辨率 0.0375 m
下载: 导出CSV
表 4 运动误差条件下的3维成像结果误差分析
Table 4. 3-D imaging performance analysis under motion error
成像方法 相关系数 RMSE (m) SSIM 理想条件下巴克码稀疏重航过直接成像结果 0.8759 0.0104 0.9535 运动误差下稀疏重航过直接成像结果 0.8329 0.0204 0.9133 运动误差下稀疏重航过运动误差补偿和3维成像结果 0.8781 0.0115 0.9647
下载: 导出CSV
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