基于改进U-Net的高光谱农林植被分类方法
A Hyperspectral Classification Method for Agroforestry Vegetation Based on Improved U-Net
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摘要: 针对高光谱图像中的"同谱异物"和"同物异谱"现象导致传统机器学习方法难以精确区分,以及深度学习模型处理高维遥感数据耗时较长的问题,本文以河北省雄安新区雄县雄州镇马蹄湾村19种土地覆被类型(农林植被为主)为研究对象,提出一种基于改进U-Net的高光谱农林植被分类方法。该方法以U-Net为基础框架,首先利用主成分分析(Principal Component Analysis, PCA)提取主要光谱波段,降低光谱冗余度;然后提出特征提取模块,该模块使用深度可分离卷积替代U-Net中的传统卷积,提取高光谱图像多尺度特征,降低网络复杂度,并采用非线性更好的h-swish(hard-swish)激活函数提升网络的泛化性能;最后在每个特征提取模块中引入残差连接提取深层次语义信息。结果表明,改进的U-Net对19种覆被分类的整体精度为96.68%,与Mobile-UNet、U-Net、Res-UNet相比,精度分别提高了4.47%、2.92%、0.45%,训练时间较分类精度相近的Res-UNet减少了23.5%。由此可知,残差连接提升了网络分类精度,使模型在描述植被边缘和细节方面表现良好;深度可分离卷积使模型轻量化,减小训练时间;改进的U-Net模型能够准确、快速地对研究区的农林植被进行区分。Abstract: In view of the difficulty in accurately distinguishing between “same spectrum foreign objects” and “same object foreign spectrum” in hyperspectral images caused by traditional machine learning methods, and the time-consuming processing of high-dimensional remote sensing data by deep learning models, 19 land cover types(mainly agroforestry vegetation) in Matiwan village, Xiong’an New Area, Hebei Province, were taken as the research object, and a hyperspectral classification method for agroforestry vegetation based on improved U-Net was proposed. This method was based on U-Net framework. Firstly, Principal Component Analysis(PCA) was used to extract the main spectral bands to reduce spectral redundancy. Then, the feature extraction module was proposed, which used the depthwise separable convolution to replace the traditional convolution in U-Net to extract multi-scale features of hyperspectral images to reduce the complexity of the network, and uses the better nonlinear h-swish(hard-swish) activation function to improve the generalization performance of the network. Finally, residual connection was introduced into each feature extraction module to extract deep semantic information and improve the classification accuracy. The results showed that the overall accuracy of the improved U-Net for 19 cover classification was 96.68%, which was 4.47%, 2.92% and 0.45% higher than that of Mobile-UNet, U-Net and Res-UNet, respectively, and the training time was 23.5% less than that of Res-UNet with similar classification accuracy. Therefore, residual connection improved the accuracy of network classification and made the model perform well in describing vegetation edges and details. Depthwise separable convolution made the model lightweight and reduced the training time. The improved U-Net model can accurately and rapidly distinguish agroforestry vegetation in the study area.
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