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北方森林乔木层碳储量的估计及空间分析

Estimation and Spatial Analysis of Carbon Storage in Tree Layers of Northern Forests

  • 摘要: 利用遥感的方式对森林乔木层碳储量(Aboveground Biomass Carbon Stocks,ABGCS)以及乔木层碳储量的光饱和值进行精准估测,以期替代传统大面积调查的繁琐工序,为碳储量的估测提供参考和依据,提高森林可持续经营管理的效率。以2017年黑龙江省伊春市嘉荫县森林乔木层碳储量(ABGCS)作为研究对象,利用Landsat8 OLI遥感影像以及森林资源二类调查数据,构建参数模型多元逐步回归模型(Stepwise Multiple-Regression,SMR),非参数模型BP神经网络模型(BP neural network,BP-NN)、随机森林模型(Random Forest,RF)、支持向量回归模型(Support Vector Machine,SVR)对嘉荫县地区ABGCS进行估测和反演其空间分布情况。研究结果表明,非参数模型的估测精度明显高于参数模型,其中3种非参数模型(BP-NN、RF、SVR)相较于参数模型(SMR),拟合精度分别提高了25.0%、12.2%、7.3%;综合比较4种模型十折交叉验证的评价指标,分析得出模型性能优劣为BP-NN>RF>SVR>SMR,其中BP-NN模型拟合出最大的决定系数(R2为0.785)和最小的均方根误差(RMSE为3.572 t/hm2)、均方误差(MSE为12.757 t/hm2)、平均绝对误差(MAE为2.687 t/hm2);从碳储量残差分段检验结果来看,4种模型均存在碳储量不同程度上高值低估和低值高估的情况,BP-NN模型在各碳储量分段的平均残差(ME)和相对平均残差(MRE)值均为最小,其泛化能力较强;利用立方项模型确定ABGCS的光饱和值为63.056 t/hm2,与BP-NN所预测的ABGCS光饱和值接近(64.232 t/hm2)。因此,BP-NN模型在估测嘉荫县ABGCS具有较为理想的效果,为森林碳储量动态监测及研究提供重要依据。

     

    Abstract: Using remote sensing methods to accurately estimate aboveground biomass carbon stock(ABGCS) in forest canopy layers and light saturation value of carbon storage, aiming to replace the cumbersome procedures of traditional large-area surveys, providing references and basis for carbon storage estimation, and improving the efficiency of sustainable forest management. In this study, the ABGCS in Jiayin County, Yichun City, Heilongjiang Province in 2017 was selected as the research object. Landsat 8 OLI remote sensing images and forest resource two-class survey data were used to construct parameter models of stepwise multiple regression model(SMR), non-parameter models of BP neural network model(BP-NN), random forest model(RF), support vector regression model(SVR) to estimate and reverse the spatial distribution of ABGCS in Jiayin County. The research results showed that the estimation accuracy of non-parameter models was significantly higher than that of parameter models. Among them, the fitting accuracy of the three non-parameter models(BP-NN, RF, SVR) was increased by 25. 0%, 12. 2%, and 7. 3%, respectively, compared with the parameter model(SMR). By comprehensive comparison of the evaluation indexes of the four models in ten-fold cross-validation, the performance of the models was analyzed: BP-NN>RF>SVR>SMR, among which the BP-NN model fitted the largest R~2(0. 785) and the smallest RMSE(3. 572 t/hm~2), MSE(12. 757 t/hm~2), MAE(2. 687 t/hm~2). From the perspective of carbon storage residual segmentation test results, all four models exhibited varying degrees of overestimation and underestimation of carbon storage. The BPNN model had the smallest ME and MRE values in each carbon storage segment, indicating strong generalization ability. The light saturation value of ABGCS was determined to be 63. 056 t/hm~2 using a cubic model, which was close to the predicted ABGCS light saturation value by BP-NN(64. 232 t/hm~2). Therefore, the BP-NN model has a relatively ideal effect in estimating ABGCS in Jiayin County, providing important basis for dynamic monitoring and research of forest carbon storage.

     

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