Selection of parameters for simulation of net ecosystem carbon flux in Yancheng coastal wetland, Jiangsu
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摘要:
滨海湿地净生态系统碳交换量受到多种环境因素的影响,在进行滨海湿地净碳交换量估算建模时,参数的选择至关重要,如何合理地选择输入参数不仅对于估算结果的精度有影响,同时也会影响预测模型的适用性。本研究使用了Pearson、Spearman、距离相关系数、最大互信息相关系数4种相关系数来计算各个环境因素与净碳交换量之间的相关性,基于相关系数来选择最佳的输入参数组合。利用实际测得的江苏盐城盐沼湿地数据,依次选择各个相关性中最高的8个参数组合,基于卷积神经网络对江苏盐城滨海湿地NEE进行建模,得到了4个预测模型,并使用均方根误差和平均绝对值误差来进行模型精度的验证。研究表明,使用基于最大互信息系数得到的参数组合进行滨海湿地NEE建模时模型的精度最好,误差最小;净光合有效辐射,净辐射,地表辐射与NEE在4个相关系数中都属于强相关,表明这一类辐射类参数对滨海湿地NEE的影响要大于其他参数;各参数与NEE之间的关系既包含线性关系也包含非线性关系,传统的单一线性分析手段无法完整准确地反应各个环境参数与NEE之间的响应关系;基于卷积神经网络的滨海湿地NEE预测模型在精度上要优于其它同类型模型,这表明使用该模型在进行NEE预测建模时具有很好的适用性。
Abstract:The net ecosystem carbon exchange (NEE) of coastal wetland is affected by various environmental factors. The selection of parameters is very important for estimating and modeling the NEE of coastal wetland. How to reasonably select the input parameters affects not only the accuracy of the estimation results, but also the applicability of the prediction model. Four correlation coefficients were used, including the Pearson correlation coefficient, the Spearman correlation coefficient, the distance correlation coefficient, and the correlation coefficient of maximum mutual information, to calculate the correlation between various environmental factors and NEE, according to which the best combination of input parameters was chosen. Using the measurement data of the Yancheng salt marsh wetland in Jiangsu Province, eight parameter combinations with the highest correlation were selected, then eight factors were input into the convolutional neural network for model training, and finally four prediction models obtained. The root mean square error and mean absolute error were used to verify the accuracy of the model. After calculation, the root mean square errors of the four models were 0.0134, 0.0092, 0.0109, 0.0051, and the absolute errors were 0.064, 0.068, 0.0574, 0.0439, respectively. This study shows that: 1) to model the NEE of coastal wetland with the parameter combination based on the maximum mutual information coefficient, the photosynthetic effective radiation, surface radiation, net radiation, photosynthetic effective radiation, soil albedo, air temperature, relative humidity, surface temperature, and soil moisture content, the accuracy of the modeling is the best and the error is the smallest. 2) Among 15 parameters used, the net photosynthetic effective radiation, net radiation, surface radiation, and NEE are strongly correlated in the four correlation coefficients, which showed that radiation parameter had a greater impact on wetland carbon cycle than other parameters. 3) Relationship between each parameter and NEE included both linear and nonlinear relationships. The conventional single linear analysis method cannot completely and accurately reflect the response relationship between each environmental parameter and NEE. In the future works, we shall not only study the linear relationship among variables but also pay more attention to the nonlinear mutual relationship. 4) The accuracy of the coastal wetland NEE prediction model based on convolutional neural network was better than other similar models’, which shows that the model is applicate in NEE prediction modeling. This study provided a reference for NEE prediction modeling and analysis of coastal wetland in the future.
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Key words:
- convolutional neural network /
- correlation coefficient /
- coastal wetland /
- NEE
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表 1 观测参数符号及名称
Table 1. Symbols and names of the variables
符号 参数名称 符号 参数名称 RG 地表辐射 WDir 风向 PPDF 光合有效辐射 APre 气压 RN 净辐射 Rain 降雨量 ATemp 气温 WSpee 风速 RH 相对湿度 Vapor 蒸汽压 TS 土壤温度 SWC 土壤含水量 Temp 地表温度 ALB 土壤反照率 NEE 净生态系统碳交换量 表 2 Pearson相关系数计算结果Table2 Pearson correlation coefficient calculation results
参数名称 Rp 参数名称 Rp RG 0.607 8 RN 0.599 3 PPDF 0.613 9 ALB 0.000 1 ATemp 0.446 1 RH 0.362 6 Temp 0.343 7 SWC 0.033 8 WDir 0.020 6 TS 0.120 6 Vapor 0.023 0 APre 0.056 1 WSpee 0.153 7 Rain 0.027 6 表 3 Spearman相关系数计算结果
Table 3. Results of the Spearman coefficient calculation
参数名称 Rs 参数名称 Rs RG 0.683 5 RN 0.638 8 PPDF 0.672 6 ALB 0.236 7 ATemp 0.484 5 RH 0.442 1 Temp 0.355 0 SWC 0.086 3 WDir 0.054 5 TS 0.134 5 Vapor 0.039 0 APre 0.035 0 WSpee 0.183 6 Rain 0.034 1 表 4 距离相关系数计算结果
Table 4. Results of distance coefficient calculation
参数名称 dCor 参数名称 dCor RG 0.651 4 RN 0.638 2 PPDF 0.655 2 ALB 0.207 6 ATemp 0.491 0 RH 0.419 2 Temp 0.366 3 SWC 0.145 6 WDir 0.212 2 TS 0.179 9 Vapor 0.146 1 APre 0.117 2 WSpee 0.176 2 Rain 0.046 9 表 5 最大信息系数计算结果
Table 5. Results of the maximal information coefficients calculation
参数名称 参数名称 RG 0.539 6 RN 0.522 7 PPDF 0.494 7 ALB 0.403 6 ATemp 0.275 7 RH 0.247 4 Temp 0.213 4 SWC 0.195 0 WDir 0.170 8 TS 0.139 5 Vapor 0.121 6 APre 0.103 3 WSpee 0.099 0 Rain 0.078 1 表 6 参数组合
Table 6. Combination of the parameters
相关系数计算方法 参数组合 Pearson相关系数 光合有效辐射,地表辐射,净辐射,气温,
相对湿度,地表温度,风速,土壤温度Spearman相关系数 地表辐射,光合有效辐射,净辐射,气温,
相对湿度,地表温度,土壤反照率,风速距离相关系数 光合有效辐射,地表辐射,净辐射,气温,
相对湿度,地表温度,风向,土壤反照率最大信息系数 地表辐射,净辐射,光合有效辐射,土壤反照率,气温,相对湿度,地表温度,土壤含水率 表 7 误差计算结果
Table 7. Results of calculation error
均方根误差 绝对值误差 CNN_Model1 0.013 4 0.064 0 CNN_Model2 0.009 2 0.068 4 CNN_Model3 0.010 9 0.057 4 CNN_Model4 0.005 1 0.043 9 -
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