基于改进残差结构的空-谱融合轻量网络用于大范围农作物分类

Spatial-spectral Fusion Lightweight Network Based on Improved Residual Structure for Large Scale Crop Classification

  • 摘要: 现有高光谱图像分类网络在小范围、高空间分辨率的基准数据集测试时常采用大量的网络参数拟合数据特征,使其在分类方面展示出良好性能。然而实际生产任务中使用的卫星高光谱数据通常分辨率较低、覆盖范围广大,过多的网络参数容易导致过拟合问题。针对上述问题,本文提出一种新的轻量化卷积网络,并使用具有32波段、10米分辨率的珠海一号高光谱影像对沈阳市进行主要农作物(玉米、水稻)的提取。该网络分别针对影像的空间特性和光谱特性设计网络组件,再设计自适应融合的模块组件来综合空间特征与光谱特征,实现高光谱影像分类。其中,空间特征学习模块设计改进多尺度残差映射块,可以在尺度各异的多分支卷积核中自适应地检测空间特征,再进行基于注意力机制的空间特征优化。光谱特征学习模块则考虑图像中丰富的光谱信息,引入时序卷积网络的思想,通过在光谱维度的连续卷积块学习图像的精细光谱特征。这种端到端的分类网络通过卷积同时提取空间信息与光谱信息,从而实现精确推理。该方法在测试集上的总体精度OA和MIoU分别为92.3%和77.9%,玉米、水稻和其它类的单类F1-score分别达到85.1%、81.95%和94.9%,优于所有对比网络。通过本文数据集上的实验证明,本文方法比其他现有网络取得了更好的分类结果。这种端到端的轻量级分类网络通过不同的卷积块同时提取空间和频谱信息,有效地利用了图像的空间上下文信息和光谱通道之间的相关性。

     

    Abstract: Objectives: Deep learning methods with massive parameters have shown good performance in classifying hyperspectral image with small size and high resolution. Meanwhile, there are at risk of overfitting and difficulty in training, due to the low resolution and large size (i.e., diversity) of satellite hyperspectral data in practical applications. Thus, we proposes a new lightweight convolutional network to extract the main crops (corn, rice) in Shenyang City, by use of Orbita Hyperspectral Satellite (OHS) images with 32 spectral bands ranging from 0.4~1.0μm and 10-meters spatial resolution. Methods: First, improved multi-scale residual mapping blocks and a spatial feature optimization block based on attention mechanism are designed to formulate the spatial feature learning module. Then, spectral feature learning module with three successive 1D convolution blocks is conducted to mine the rich spectra information of HSIs. Finally, a fusion classification module is built to classify pixels by integrating weighted spatial features and spectral features. Results: Four recent networks including PSPNet, UNet, MAPNet and FreeNet are considered for comparison. From the perspective of model size, the proposed network is much lighter than PSPNet, UNet, MAPNet and equal to FreeNet, which is benefited from the use of 1D convolution and 2D convolution in two learning modules that avoid excessive parameters caused by 3D convolution. From the perspective of accuracy, considering the overall assessment metrics and the F1-score of each category, the proposed method achieves the best performance over the recent four networks. The OA and MIoU of our method on the test set are 92.3% and 77.9% respectively which is superior to other networks. Our method also has a better classification result in single category. The F1-score of corn, rice and other each reach 85.1%, 81.95% and 94.9%. Expecially for rice, the F1-score of our method is 11.5%, 4.2%, 13.6% and 12.0% higher than PSPNet, UNet, MAPNet and FreeNet respectively. Conclusions: Experiments on the data set show that our method achieves better classification results than other existing networks. This end-to-end lightweight classification network extracts spatial and spectral information simultaneously by different convolutional blocks. The idea of combining spatial and spectral features can effectively utilize the spatial context information of images and the correlation among spectral channels to improve classification accuracy.

     

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