An Aircraft Detection Method Based on Convolutional Neural Networks in High-Resolution SAR Images
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摘要: 传统的合成孔径雷达(Synthetic Aperture Radar, SAR)图像飞机检测方法一般利用像素对比度信息进行图像分割,从而提取待定目标。然而这些方法只考虑了像素亮度信息而忽视了目标的结构特征,进而导致目标的不精确定位和大量虚警的产生。基于上述问题,该文构建了一个全新的SAR图像飞机目标检测算法框架。首先,针对大场景SAR图像应用需求,提出了改进的显著性预检测方法,从而实现SAR图像候选飞机目标多尺度快速粗定位;然后,设计并调优了含4个权重层的卷积神经网络(Convolutional Neural Network, CNN),实现对候选目标的精确检测和鉴别;最后,因为SAR数据量有限、易导致过拟合,提出4种适用于SAR图像的数据增强方法,具体包括平移、斑点加噪、对比度增强和小角度旋转。实验证实该飞机检测算法在高分辨率TerraSAR-X数据集上效果显著,与传统的SAR飞机检测方法相比,该方法检测效率更高,泛化能力更强。
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关键词:
- 合成孔径雷达(SAR) /
- 飞机检测 /
- 卷积神经网络(CNN) /
- 数据增强 /
- 视觉显著性
Abstract: In the field of image processing using Synthetic Aperture Radar (SAR), aircraft detection is a challenging task. Conventional approaches always extract targets from the background of an image using image segmentation methods. Nevertheless, these methods mainly focus on pixel contrast and neglect the integrity of the target, which leads to locating the object inaccurately. In this study, we build a novel SAR aircraft detection framework. Compared to traditional methods, an improved saliency-based method is proposed to locate candidates coarsely and quickly in large scenes. This proposed method is verified to be more efficient compared with the sliding window method. Next, we design a convolutional neural network fitting in SAR images to accurately identify the candidates and obtain the final detection result. Moreover, to overcome the problem of limited available SAR data, we propose four data augmentation methods comprising translation, speckle noising, contrast enhancement, and small-angle rotation. Experimental results show that our framework achieves excellent performance on the high-resolution TerraSAR-X dataset. -
表 1 CNN参数
Table 1. Parameters of our CNN
层结构 核结构 输出尺寸 输入层 – 120×120 C1 32@5×5 116×116 S1 2×2 58×58 C2 64@5×5 54×54 S2 2×2 27×27 C3 128@6×6 22×22 S3 2×2 11×11 表 2 不同预检测方法性能比较
Table 2. The performance of different pre-detection methods
方法 预检测 正确率(%) 候选目标 个数 预检测 时间(s) Selective search 100 569 47.50 原始显著性预检测 94.12 298 6.07 改进的显著性预检测 100 242 10.67 表 3 不同数据增强方法的检测正确率
Table 3. Accuracy rates of CNN with different augmentation methods
操作 检测正确率(%) 原始 86.33 平移 92.01 斑点加噪 93.74 对比度增强 93.64 小角度旋转 92.76 综合4种增强方法 96.36 表 4 不同网络层数的检测正确率比较
Table 4. Accuracy rates of CNN with different number of layers
网络结构 检测正确率(%) C1: 32@5×5, S1, C2: 64@5×5, S2, C3: 128@6×6, S3, C4: 256@6×6, S4 95.99 C1: 32@5×5, S1, C2: 64@5×5, S2, C3: 128@6×6, S3 (本文) 96.36 C1: 32@5×5, S1, C2: 64@5×5, S2 93.70 表 5 不同卷积核个数的检测正确率比较
Table 5. Accuracy rates of CNN with different number of kernels
网络结构 检测正确率(%) C1: 16@5×5, S1, C2: 32@5×5, S2, C3: 64@6×6, S3 93.93 C1: 32@5×5, S1, C2: 64@5×5, S2, C3: 128@6×6, S3 (本文) 96.36 C1: 64@5×5, S1, C2: 128@5×5, S2, C3: 256@6×6, S3 95.05 表 6 不同卷积核大小的检测正确率比较
Table 6. Accuracy rates of CNN with different size of kernels
网络结构 检测正确率(%) C1: 32@3×3, S1, C2: 64@3×3, S2, C3: 128@3×3, S3 95.96 C1: 32@5×5, S1, C2: 64@5×5, S2, C3: 128@6×6, S3 (本文) 96.36 C1: 32@5×5, S1, C2: 64@5×5, S2, C3: 128@5×5, S3 96.16 表 7 不同方法在同一数据集上的平均检测率
Table 7. Average detection rates of different methods on the same dataset
方法 检测正确率(%) CNN 96.36 SVM 92.64 HOG+SVM 93.79 AdaBoost 92.28 -
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