协同Sentinel-2和GF-3多特征优选的农作物识别

    Crop identification by synergistic Sentinel-2 and GF-3 multi-feature optimization

    • 摘要: 农作物识别是精准农业的重要研究领域。在时空大数据和智能计算时代,如何充分挖掘和综合应用各种数据、方法和模型的优势是提高遥感农作物识别精度的有效途径。该研究以安徽省颍上县为例,采用Sentinel-2和GF-3卫星影像数据,提取了包括光谱、指数、纹理和极化等在内的58个特征指标;随后分别选取3种特征优选算法和3种机器学习方法进行组合,设计了3种试验方案,探索特征选择和机器学习方法对农作物分类的影响;通过对比特征维度和分类精度,对各种分类方案进行评价。研究结果显示:红边特征在农作物识别中具有重要作用,同时纹理特征的加入也适当提高了分类精度;3种特征优选算法分别和随机森林方法组合时,分类精度均为最优;其中Relief F与随机森林组合在遥感农作物识别分类中效果最好,总体精度达到了93.39%,Kappa系数为0.8933,F1得分为93.31%;比Relief F结合极限梯度提升和支持向量机分类方法的总体精度、Kappa系数、F1得分分别提高1.36个百分点、0.021和1.31个百分点,8.81个百分点、0.1312和8.78个百分点;在随机森林分类方法下,Relief F特征选择维度为28维,比随机森林的递归特征消除和卡方检验特征优选算法分别低4和22维,证明了Relief F结合随机森林分类方法的有效性和先进性。该研究为精准农作物识别提供了新的技术思路。

       

      Abstract: Global climate has posed the significant challenges on agricultural production and food security in recent years. Alternatively, satellite remote sensing can be expected to timely and accurately monitor the crop types and planting structures in precision agriculture. An agricultural survey is then required to estimate the crop yields and disaster impacts. Existing remote sensing data and ground sample can also be fully utilized to combine with feature engineering techniques and machine learning. The accuracy of crop classification can be enhanced after quantitative remote sensing using satellite-derived spatiotemporal big data. However, there are the substantial variations in the feature selection algorithms and machine learning under different scenarios, leading to the significant fluctuations in the recognition and classification accuracy. Therefore, it is very necessary for the individual remote sensing imagery and multi-feature selection during crop recognition and classification. This study aims to realize the crop identification using synergistic Sentinel-2 and GF-3 multiple feature optimization. The study area was taken from the Ying Shang County in Anhui Province, China. Sentinel-2 and GF-3 satellite imagery data was employed to extract 58 feature indicators, including spectral, index, texture, and polarization characteristics. Subsequently, three algorithms of feature selection and three machine learning were combined to design three experimental schemes, in order to explore the effects of feature selection and machine learning techniques on the crop classification. Feature dimensions and classification accuracy were then compared to evaluate the effectiveness of various classification schemes. Several key insights revealed that: (1) The feature selection algorithms were effectively reduced the dimensionality to avoid the data redundancy associated with excessively high dimensions. After that, Relief F algorithm performed the best to reduce the feature dimensions with the effective performance of crop classification. Specifically, Relief F selected 28 features, which was 4 fewer than the number selected by RF_RFE and 22 fewer than those selected by CST. (2) A comparative analysis was performed on the three algorithms of feature selection. It was found that the red-edge feature bands (B5, B6, and B7) were emerged in three algorithms during crop classification. Additionally, the bands B11 and B12 with texture features were further enhanced the accuracy of crop recognition. Different algorithms were varied in the preferences during feature selection; Specifically, Relief F algorithm was tended to favor the spectral and index features. (3) Three machine learning revealed that the combination of Relief F with Random Forest (RF) was achieved in the highest accuracy of crop classification in the study area. While the XGBoost and Support Vector Machine (SVM) shared the inferior performance. In Relief F feature selection, the RF was achieved in an overall accuracy of 93.39%, a Kappa coefficient of 0.8933, and an F1 score of 94.31%. These results indicated that the RF outperformed the XGBoost and SVM by 1.36 percentage point, 0.021 and 1.31 percentage point, while by 8.81 percentage point, 0.1312 and 8.78 percentage point, respectively. This experiment was strongly validated the effectiveness and advanced nature of combined Relief F feature selection with RF classification. Feature selection with suitable machine learning can be expected to significantly enhance the classification performance under various agricultural contexts. These findings can greatly contribute to the effective utilization of remote sensing technologies in agricultural monitoring and decision-making. The relationship between feature selection and classification accuracy can also provide the technical approach for the recognition and classification in precision agriculture.

       

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