黑河流域中上游水热通量足迹模型的对比分析

Comparison of Footprint Models of Surface Heat and Water Vapor Fluxes in the Middle and Upper Reaches of Heihe River Basin

遥感技术是获取区域地表水热通量的重要手段,利用地面观测值对遥感估算水热通量进行验证时,存在空间尺度不匹配的问题,结合足迹分析可以较好地解决这一问题,为遥感蒸散发模型提供空间尺度匹配的验证数据。利用黑河流域上游阿柔超级站和中游大满超级站的涡动相关仪观测数据,对常用的3种水热通量足迹模型Kormann&Meixner(KM)模型、Kljun模型和Hsieh模型的输入参数进行了敏感性分析,并比较和分析了3个模型单时次和日尺度的足迹结果差异,为足迹模型的合理选用提供参考依据,以服务于数据质量判别和遥感模型的验证。结果表明:①奥布霍夫长度(L)是KM模型和Hsieh模型的敏感因子,L值变化时,Hsieh的足迹结果变化大于KM,而Kljun模型对L的敏感程度不高;观测高度(z_(m))和侧向风速标准差(σ_(v))也是3个模型的敏感因子。②单时次30 min尺度上,KM和Hsieh的通量贡献源区大小和形状吻合较好,但与Kljun足迹结果存在显著差异;Kljun的源区范围明显较小,上风向通量贡献峰值明显大于KM和Hsieh,且上风向通量贡献峰值的位置明显小于另外两个模型。③日尺度上,3种足迹模型的水热通量源区形状相似,Kljun模型的源区范围最小。实验结果为足迹模型的合理选用提供参考依据,以服务于碳、水热通量数据质量判别和遥感模型的验证。

Remote sensing is an important method to obtain regional surface heat and water vapor fluxes,howev⁃er there is a mismatch of spatial scale between the observation data and remotely-sensed data when the remote⁃ly-sensed data is verified.Combined with footprint analysis,this problem can be better solved,providing a ref⁃erence basis for the verification of remote sensing models.Based on the eddy covariance data from the Arou sta⁃tion in the upper reaches of the Heihe River basin and the Daman Superstation in the middle reaches,the sensi⁃tivity analysis of the input parameters of three commonly used flux footprint models,namely Kormann&Mei⁃xner model(hereafter referred as KM),Kljun model and Hsieh model was performed,and the difference in the footprint results of the three models at single time and daily scales is compared and analyzed.The objective of this study is not only to provide a reference basis for the reasonable selection of footprint model,but also to serve for the discrimination of data quality and the verification of relevant remote sensing models.The results showed that:(1)The KM and Hsieh models are very sensitive to the Obukhov length(L).When L changes,the footprint result of Hsieh model varies much more than that of KM model,while Kljun model is less sensitive to L.Observation height(z_(m))and standard deviation of lateral wind fluctuations(σ_(v))are also sensitive factors of the three models.(2)On the every 30 min time scale,the footprint results between KM and Hsieh models are in good agreement in extent and shape,but there are significant differences with Kljun model.The footprint ex⁃tent of Kljun model is obviously smaller,while the estimated position of maximum flux contribution is much larger as compared to KM and Hsieh models.The peak distance of the footprint to the tower is obviously small⁃er than that of the other two models.(3)On a daily time scale,the flux contribution source area of the three models are similar in shape,but the source region of the Kljun model is the smallest.The results of this study provide important information for the selection of proper footprint models,which is used for data quality control and remotely-sensed products evaluation.