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基于机器学习的机载G波段微波辐射计反演大气水汽与液态水路径研究

Research on Retrieval of Precipitable Water Vapor and Liquid Water Paths Using the Airborne G-band Water Vapor Radiometer Based on Machine Learning

  • 摘要: 高精度水汽总量(Precipitable Water Vapor,PWV)和云液态水路径(Liquid Water Path,LWP)测量对提升天气预报准确性和气候模式评估精度具有重要意义。本文基于北京市人工影响天气中心空中国王飞机平台搭载的G波段微波辐射计(G-band Water Vapor Radiometer,GVR)和综合气象要素测量系统AIMMS-20(Aircraft-Integrated Meteorological Measurement System)观测数据,结合北京探空站2009~2023年历史探空廓线,利用主被动微波辐射传输模式(Passive and Active Microwave TRAnsfer ,PAMTRA)辐射传输模式构建训练集和验证集,其中2021~2023年作为验证集,建立三类机器学习反演算法——后向传播神经网络(Backpropagation Neural Network,BP)、极限梯度提升(Extreme Gradient Boosting,XGBoost)和随机森林(Random Forest,RF),实现了PWV和LWP的高精度反演。基于独立探空廓线数据的验证结果表明,新建机器学习算法反演的PWV均方根误差(Root Mean Square Error,RMSE)优于0.62 mm,LWP RMSE优于0.04 mm,新建机器学习算法均显著优于GVR自带的反演算法。针对GVR一次实测亮温数据的反演结果表明,各算法反演的PWV与LWP时间演变趋势基本一致,而GVR自带算法存在系统性低估,其与RF算法的PWV和LWP最大偏差分别达3.82 mm和0.24 mm。在考虑±1 K仪器误差的敏感性分析中,GVR自带算法稳定性最差,其反演的平均绝对偏差(Mean Absolute Error,MAE)最大(PWV MAE:0.19 mm,LWP MAE:0.02 mm),而新建的BP神经网络表现出最优的抗干扰能力。

     

    Abstract: High-precision measurements of Precipitable Water Vapor (PWV) and Liquid Water Path (LWP) are crucial for enhancing weather forecast accuracy and evaluating climate models. This study utilizes observational data from the G-band Water Vapor Radiometer (GVR) and the Aircraft Integrated Meteorological Measurement System (AIMMS-20) mounted on the Beijing Artificial Weather Modification Center"s King Air aircraft, combined with historical sounding profiles (2009–2023) from the Beijing Sounding Station. Using the passive and active microwave radiation transfer mode (PAMTRA) to generate training and validation datasets, with data from 2021 to 2023 reserved as the validation set, we developed three machine learning algorithms—Backpropagation Neural Network (BP), Extreme Gradient Boosting (XGBoost), and Random Forest (RF)—for high-precision PWV and LWP retrieval. Validated against independent radiosonde profiles, the newly developed machine learning algorithm demonstrates superior performance, with RMSEs of 0.62 mm for precipitable water vapor and 0.04 mm for liquid water path, significantly outperforming the GVR system"s built-in retrieval algorithm. Analysis of GVR-measured brightness temperature data reveals that while all algorithms capture consistent temporal trends in PWV and LWP, the GVR"s built-in algorithm exhibits systematic underestimation, with maximum deviations reaching 3.82 mm for PWV and 0.24 mm for LWP compared to the RF algorithm. Furthermore, in sensitivity tests incorporating ±1 K instrument errors, the built-in algorithm demonstrates the poorest stability, yielding the largest Mean Absolute Error (MAE) (0.19 mm for PWV, 0.02 mm for LWP), whereas the newly developed BP neural network exhibits the strongest noise resistance.

     

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