A Model for Predicting Ship Emission Pollutants Based on MASTGCN Using AIS Information
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摘要: 船舶排放的二氧化硫(SO2)是导致大气污染和海洋酸化的主要因素之一,其时空分异性显著且不均,当前船舶污染物预测模型在时空依赖性建模方面存在局限性,难以有效捕捉船舶SO2排放中的复杂时空关联特征。针对该问题,基于船舶自动识别系统(automatic identification system,AIS)数据及中国船舶基础信息数据,采用动力学方法结合排放因子量化船舶航行过程中的SO2排放量,为后续预测提供了数据支持。在预测模型构建方面,研究了融合多头自注意力机制的时空图卷积网络(multi-head attention spatial-temporal graph convolutional network,MASTGCN)预测模型。该模型以时空图卷积网络(spatial-temporal graph convolutional network,STGCN)为基础架构,在空间和时间维度中引入多头自注意力机制,通过动态权重分配强化对不同区域间空间关联性以及不同时段间时间关联性的建模能力,实现对船舶SO2排放的时空预测。实验结果表明,在注意力头数为5时,模型的平均绝对误差(mean absolute error,MAE)、均方误差(mean squared error,MSE)、均方根误差(root mean squared error,RMSE)以及浮点运算数(floating point operations,FLOPs)分别为0.057 5、0.120 6、0.347 3、3 030 M,模型准确度和计算复杂度的综合性能优于其他头数配置及STGCN模型。相较于STGCN模型,MAE、MSE、RMSE和FLOPs指标分别提高了27.6%、6.0%和1.3%。研究结果表明,多头注意力机制可以通过动态权重分配有效捕获船舶SO2排放的空间特征,5个注意力头的MASTGCN模型在预测精度上表现优秀,同时在计算复杂度方面保持相对合理。Abstract: Sulfur dioxide (SO2) emissions from ships are a major contributor to air pollution and ocean acidification, exhibiting significant spatial and temporal heterogeneity. Current prediction models for shipborne pollutants have limitations in modeling spatiotemporal dependencies, making it difficult to effectively capture the complex spatiotemporal correlation characteristics in SO2 emissions. To address this issue, based on automatic identification system (AIS) data and Chinese ship registry data, a dynamics-based method combined with emission factor approaches is used to quantify shipborne SO2 emissions during navigation, thereby providing a solid data foundation for subsequent prediction. In terms of model construction, a multi-head attention spatial-temporal graph convolutional network (MASTGCN) is proposed. Based on the spatial-temporal graph convolutional network (STGCN) architecture, MASTGCN incorporates multi-head self-attention mechanisms in both spatial and temporal dimensions. By dynamically allocating weights, it enhances the modeling capability to learn spatial dependencies across different regions and temporal dependencies across time intervals, thus improving the accuracy of spatiotemporal predictions for shipborne SO2 emissions. Experimental results show that when the number of attention heads is set to five, the model achieves a mean absolute error (MAE) of 0.057 5, mean squared error (MSE) of 0.120 6, root mean squared error (RMSE) of 0.347 3, and floating point operations (FLOPs) of 3 030 M. These results demonstrate superior overall performance in both accuracy and efficiency compared to other configurations and the baseline STGCN model. Specifically, MASTGCN with five attention heads outperforms STGCN by improving MAE by 27.6%, MSE by 6.0%, and RMSE by 1.3%. The findings indicate that the incorporation of multi-head attention mechanisms enables the model to effectively capture the spatial characteristics of SO2 emissions through dynamic weighting. The five-head MASTGCN model achieves excellent predictive accuracy while maintaining a relatively reasonable computational complexity.
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表 1 设备排放因子
Table 1. Emission factors for equipment
设备 含硫量/ % $ \mathrm{SO}_{2} $排放因子$ /(\mathrm{g} /(\mathrm{kW} \cdot \mathrm{h})) $ 燃油消耗量$ /(\mathrm{g} /(\mathrm{kW} \cdot \mathrm{h})) $ 主机 0.50 2 203 辅机 0.50 2.1 217 锅炉 0.50 2.8 290 表 2 实验环境
Table 2. Experimental environment
名称 型号版本 中央处理器(CPU) Intel(R)Xeon(R)Platinum 8358 CPU 图形处理器(GPU) NVIDIA Tesla-A40-48G 内存/GB 128 系统盘/数据盘GB 20/50 操作系统 Ubuntu 20.04 Python 3.8 PyTorch 2.0.0 CUDA 12.2 表 3 网络超参数设置
Table 3. Network hyperparameter settings
超参数 设置值 学习率 0.001 迭代次数 96 优化器 Adam 批量大小 32 时间步长 12 表 4 不同模型性能对比分析表
Table 4. Comparative analysis of the performance of
模型 MAE MSE RMSE ARIMA 0.6949 1.9240 0.9003 DT 0.0757 0.2793 0.5285 LR 0.0621 0.1490 0.3860 GRU 0.0654 0.1276 0.3572 LSTM 0.0612 0.1375 0.3709 Transformer 0.0998 0.0628 0.2506 CNN+LSTM 0.0608 0.1413 1.2441 STGCN 0.0794 0.1283 0.3520 MASTGCN 0.0575 0.1206 0.3473 表 5 不同头数性能对比分析表
Table 5. Comparative analysis of the performance of different head counts
模型 HEAD MAE MSE RMSE STGCN 0.0794 0.1283 0.3520 1 0.0590 0.1218 0.3490 2 0.0620 0.1222 0.3496 MASTGCN 3 0.0611 0.1202 0.3467 4 0.0642 0.1188 0.3446 5 0.0575 0.1206 0.3473 6 0.0598 0.1174 0.3427 表 6 不同头数模型复杂度对比分析表
Table 6. Comparison and Analysis of Model Complexity with Different Numbers of Heads
模型 HEAD Parameters FLOPs/M STGCN 57096 866 1 66120 1298 2 75064 1731 MASTGCN 3 84008 2164 4 92952 2597 5 101896 3030 6 110840 3463 -
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