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基于不同机器学习算法的无人机高光谱影像树种分类研究

Tree Species Classification in UAV Hyperspectral Images Based on Different Machine Learning Algorithms

  • 摘要: 机载高光谱数据能够反映树种光谱特征,可以对森林树种进行精确分类。应用不同机器学习分类算法对无人机高光谱影像进行树种分类研究。首先利用无人机完成黑龙江省帽儿山实验林场研究区的高光谱数据采集,对获取数据进行一系列预处理;然后分别利用基于高斯核的支持向量机、随机森林、K-近邻3种不同机器学习分类算法建立基于全波段高光谱数据的树种分类模型,并基于不同波段选择方法(连续投影算法、竞争性自适应重加权法以及无信息变量消除法)对全波段高光谱数据降维后再进行树种分类模型构建;最后联合不同波段选择方法与高光谱图像纹理特征构建树种分类模型,并对不同处理方法结果进行比较。研究表明,对于全波段高光谱数据的树种分类模型中,基于高斯核的支持向量机分类准确率最高(87.55%)。不同波段选择后,随机森林稳定性是3种分类算法中最好的,准确率较高,而基于高斯核的支持向量机分类准确率随着特征维度的增加而提升。基于灰度共生矩阵提取纹理特征后结合波段选择建立的树种分类模型准确率高于单一的波段选择建立的模型,尤其是K-近邻分类算法的提升最大,说明具有明显划分的特征进行其建模可达到较好分类效果。该研究利用不同特征选择方式结合3种不同的机器学习分类算法实现了基于高光谱数据的优势树种分类,为波段选择方式与机器学习算法结合提供了技术参考,也对基于无人机高光谱数据的森林生物量反演和碳储量估测研究具有重要意义。

     

    Abstract: Airborne hyperspectral data can reflect the spectral characteristics of tree species, which can be used for precise classification of forest tree species. This study applies different machine-learning classification algorithms to classify tree species in hyperspectral images of unmanned aerial vehicles(UAV). Firstly, a UAV was used to collect hyperspectral data from the Maor Mountain Experimental Forest Farm in Heilongjiang Province, and a series of preprocessing was completed for the obtained data. Then, three different machine learning classification algorithms, namely, support vector machine(SVM) based on Gaussian kernel, random forest(RF), and K-nearest neighbor(KNN), were used to establish the tree species classification models, respectively, based on the fullband hyperspectral data. Meanwhile, tree species classification models were constructed based on the dimension-reduced full-band hyperspectral data using different band selection methods(successive projections algorithm, competitive adaptive reweighted sampling method and uninformative variable elimination method). Finally, the tree species classification model was constructed by combining different band selection methods and hyperspectral image texture features, and the results of different processing methods were compared. Research shows, the kernel SVM had the highest classification accuracy(87. 55%) among the tree species classification models with full-band hyperspectral data. After selecting different bands, the stability of RF is the best among the three classification algorithms, and the accuracy rate was high, while the classification accuracy of the support vector machine based on the Gaussian kernel improved with the increase of feature dimension. The accuracy of the tree species classification model established by extracting texture features based on a grayscale co-occurrence matrix combined with band selection was higher than that of the model established by a single band selection. In particular, the K-nearest neighbor classification algorithm has the greatest improvement, which indicated that modeling with clearly partitioned features can achieve good classification results. This study used different feature selection methods combined with three different machine learning classification algorithms to achieve dominant tree species classification based on hyperspectral data, which provides technical reference for the combination of band selection methods and machine learning algorithms, and it is also of great significance for forest biomass retrieval and carbon storage estimation based on UAV hyperspectral data.

     

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