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基于双分支全局与局部特征融合网络的县域尺度玉米产量预测方法

County-level maize yield prediction method based on dual-branch global and local feature fusion network

  • 摘要: 针对现有作物产量预测模型难以并行捕捉长短期时间依赖性的问题,该研究提出一种基于双分支全局与局部特征融合网络(dual-branch global and local feature fusion network, DGLF-Net)的深度学习模型。该方法利用卷积神经网络(convolutional neural network, CNN)与长短期记忆网络(long short-term memory, LSTM)分支捕捉局部动态与长期依赖,结合全局时序注意力分支提取非连续关键事件,并通过自适应门控模块动态融合多源特征。结果表明:1)玉米产量形成同时受全生育期累积效应和关键月份局部动态变化影响,其中7月增强植被指数(enhanced vegetation index, EVI)与产量的相关系数达 0.51;2)消融试验验证了局部时序特征提取模块(local temporal feature extractor, LTFE)、全局时序注意力模块(global temporal attention module, GTAM)和门控融合模块(gated fusion module, Gating)提升模型性能的有效性;3)DGLF-Net 性能优于各对比模型,2022 年决定系数(R2)为 0.812 0,均方根误差(RMSE)与平均绝对误差(MAE)分别为 441.95 和 325.30 kg/hm2;与 CNN-LSTM-Attention 模型相比,R2 提高了 5.52%,RMSE 与 MAE 分别降低了 9.69% 和 17.38%。4)空间独立验证表明,模型在低、中、高产县域均具有良好的泛化能力;5)早期预测显示,使用 5—9 月数据时,2022 年 R2 为 0.768 3,具备良好的早期预测能力。6)归一化植被指数(normalized difference vegetation index, NDVI)、叶绿素植被指数(chlorophyll vegetation index, CVI)与绿色归一化差异植被指数(green normalized difference vegetation index, GNDVI)组合表现较稳定;SHAP分析显示,土壤有机碳含量(soil organic carbon, SOC)、土壤容重(bulk density, Bd)和水汽压差(vapor pressure deficit, VPD)对预测结果具有重要影响。该研究能较好地反映县域产量的空间差异,且预测误差分布较为均匀,为多源时序数据驱动的县域作物产量预测提供了有效的思路和方法。

     

    Abstract: Accurate maize yield prediction is often required for regional crop growth monitoring in modern agriculture. However, existing sequential models cannot simultaneously represent continuous local temporal variations and full-season global dependencies. In this study, a deep learning model was developed to accurately predict the maize yield for early warning and spatial generalization at the county scale, according to multi-source agricultural information. A Dual-Branch Global and Local Feature Fusion Network (DGLF-Net) was developed for maize yield prediction in Jilin Province from 2009 to 2022. Moderate. The model was also integrated with the Resolution Imaging Spectroradiometer (MODIS) surface reflectance, vegetation indices, meteorological data, and soil properties. A Local Temporal Feature Extractor (LTFE), composed of a Convolutional Neural Network (CNN) and a Long Short-Term Memory (LSTM) network, was used to extract local continuous temporal features. A Global Temporal Attention Module (GTAM) was used to capture long-range temporal dependencies over the growing season. A gated fusion module (Gating) was then used to combine local temporal and global contextual information. Data from 2009 to 2020 were used for training, and data from 2021 to 2022 were used for testing. The correlation analysis showed that maize yield formation was dominated by both full-season cumulation and key-month local dynamics. Vegetation index (EVI) in July showed the strongest positive correlation with yield, with a correlation coefficient of 0.51, indicating that yield prediction depended on the remote sensing information during key growth stages. Ablation experiments confirmed the contribution rates of the main components of DGLF-Net. Furthermore, the complete model achieved a coefficient of determination (R2) of 0.812 0 in 2022, a root mean squared error (RMSE) of 441.95 kg/hm2, and a mean absolute error (MAE) of 325.30 kg/hm2. The R2 values decreased to 0.711 7 and 0.773 9, respectively, after removing GTAM and Gating. The R2 reduced to 0.605 3 in LTFE after removing CNN, while R2 reduced to 0.745 2 after removing LSTM, indicating that both local feature extraction and temporal dependency modeling contributed to prediction performance. Model comparison experiments showed that DGLF-Net outperformed random forest regression (RFR), extreme gradient boosting (XGBoost), CNN, Transformer, LSTM, CNN-Transformer, and CNN-LSTM-Attention in 2021 and 2022. DGLF-Net improved R2 by 5.52% in 2022, whereas RMSE and MAE were reduced by 9.69% and 17.38%, respectively, compared with CNN-LSTM-Attention. Spatial independent validation showed that DGLF-Net maintained stable performance in counties with different yield levels. The prediction accuracies for Ji’an, Linjiang, and Gongzhuling were 96.10%, 97.47%, and 95.08%, respectively, in 2022. Early prediction analysis showed that the model reached an R2 of about 0.77 using data from May to September, indicating a reliable prediction for one month before harvest. The vegetation index analysis showed that the combination of NDVI, CVI, and green normalized difference vegetation index (GNDVI) performed best in 2022, with an R2 of 0.826 0, RMSE of 425.30 kg/hm2, and MAE of 309.40 kg/hm2. SHapley Additive exPlanations (SHAP) analysis indicated that soil organic carbon (SOC), bulk density (Bd), and vapor pressure deficit (VPD) were stable and important features in both years. Spatial prediction maps further showed that DGLF-Net better preserved the county-level yield gradient in Jilin Province for the more balanced spatial distribution of errors. The DGLF-Net effectively improved county-level maize yield prediction using local temporal learning dynamics and global seasonal dependencies, indicating the strong prediction accuracy, early prediction potential, and spatial generalization. Future studies can further incorporate higher-resolution remote sensing data, planting density, field information, cultivar differences, and pest or disease information in more complex agricultural scenarios.

     

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