基于TDS-1数据的积雪密度反演研究

Research on snow density inversion based on TDS-1 data

  • 摘要: 积雪是冰冻圈的重要组成部分,影响着陆地、海洋与大气间的能量平衡和水分交换. 本文利用2016—2018年全球导航卫星系统反射测量(Global Navigation Satellite System Reflectrometry,GNSS-R)卫星TechDemoSat-1(TDS-1)的时延多普勒图(delay-Doppler map, DDM)等数据,讨论了基于TDS-1卫星的雪密度反演. 选择不同的比例将2016—2017年的实验数据划分为训练集和验证集,使用训练集建立随机森林(random forest,RF)、极端梯度增强等机器学习算法和卷积神经网络深度学习算法雪密度反演模型,通过验证集评估模型性能. 实验结果表明RF具有最佳反演性能,且训练集/验证集比例为7∶3时性能最佳,其平均绝对误差(mean absolute error,MAE)为18.021 5 kg/m3,均方根误差(root mean square error,RMSE)为28.700 4 kg/m3,决定系数R2为0.818 5. 在此基础上,以2018年数据作为测试集对建立的RF模型的泛化性能进行评估,MAE为42.690 9 kg/m3,RMSE为54.438 0 kg/m3R2为0.285 9. 将特征参量分为三类,沙普利加性分析(Shapley additive explanation, SHAP)和消融实验的结果表明,TDS-1特征量在反演模型当中起到了主要作用,雪层温度和风速等环境特征量起到了重要的辅助作用,TDS-1衍生特征量进一步提高了模型的精度. 分析显示,数据量分布直接影响了模型的性能,模型在数据比例最大的150~250 kg/m3雪密度区间的反演精度最佳. 实验结果证明了基于TDS-1卫星数据反演雪密度的可行性,为雪密度反演研究提供了新的思路.

     

    Abstract: Snow is an important component of the cryosphere, affecting the energy balance and water exchange between land, ocean, and atmosphere. This article discusses the feasibility of snow density inversion based on Global Navigation Satellite System Reflectrometry (GNSS-R) satellite TechDemoSat-1 (TDS-1) delay-Doppler map (DDM) data from 2016 to 2018. Select different proportions to divide the experimental data from 2016 and 2017 into training and validation sets, use the training set to establish machine learning algorithms such as random forest (RF) and extreme gradient enhancement, as well as convolutional neural network deep learning algorithms for snow density inversion models. Evaluate the model performance through the validation set The experimental results show that RF has the best inversion performance, and performs the best when dividing the data in a 7∶3 ratio. Its mean absolute error (MAE) is 18.021 5 kg/m3, root mean square error (RMSE) is 28.700 4 kg/m3, and the determination coefficient R2 is 0.818 5. On this basis, the generalization performance of the established RF model was evaluated using 2018 data as the test set. The MAE was 42.690 9 kg/m3, RMSE was 54.438 0 kg/m3, and R2 was 0.285 9. The feature parameters are divided into three categories. The results of Shapley additive explanations (SHAP) analysis and ablation experiments show that TDS-1 features play a major role in the inversion model, while environmental features such as snow layer temperature and wind speed play important auxiliary roles. TDS-1 derived features further improve the accuracy of the model. Analysis shows that the distribution of data directly affects the performance of the model, and the model has the best inversion accuracy in the snow density range of 150–250 kg/m3, where the data proportion is the highest. The experimental results have demonstrated the feasibility of using TDS-1 satellite data to invert snow density, providing new ideas for snow density inversion research.

     

/

返回文章
返回