Evaluation of the ESA CCI soil moisture product using ground-based observations
Evaluation of the ESA CCI soil moisture product using ground-based observations
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DOI：
10.1016/j.rse.2014.07.023
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发表时间：
2015-06-01
影响因子：
13.5
通讯作者：
Kidd, R.
中科院分区：
文献类型：
--
作者：
Dorigo, W. A.;Gruber, A.;Kidd, R.
在这项研究中，我们评估的技能，一个新的，合并的土壤水分产品（ECV_SM），已开发的欧洲航天局的水循环多任务观测战略和气候变化倡议项目的框架。该产品以协同的方式将四个被动（SMMR、SSM/I、TMI和AMSR-E）和两个主动（ERS AMI和ASCAT）粗分辨率微波传感器的土壤湿度反演结果合并为一个跨越1979-2010年的全球数据集。评估使用了来自全球28个历史和活跃监测网络的596个地点的地面土壤湿度观测结果。除了提供传统的协议措施，我们使用三重配置技术来评估数据集中的随机误差。ECV_SM与所有实测值的平均斯皮尔曼相关系数为0.46（绝对值）和0.36（土壤水分距平），但网间和时段间差异很大。无偏均方根差和三重配置误差显示网络之间的变化较小，平均值分别约为0.05和0.04 m（3）m（-3）。随着时间的推移，ECV_SM质量呈上升趋势，但在2007-2010年期间观察到所有性能指标持续下降。将合并的产品的技能与单独的输入产品的技能进行比较表明，除了关于ASCAT产品之外，合并的产品具有与单独的输入产品相似或更好的性能，与ASCAT产品相比，ECV_SM的性能较差。后者的原因很可能是卫星观测和现场测量之间的采样时间不匹配，以及另一方面用于将ASCAT产品整合到ECV_SM中的重新定位和缩放策略。本研究的结果将用于进一步改进缩放和合并算法，以用于未来的产品更新。(C)2014爱思唯尔公司All rights reserved.
In this study we evaluate the skill of a new, merged soil moisture product (ECV_SM) that has been developed in the framework of the European Space Agency's Water Cycle Multi-mission Observation Strategy and Climate Change Initiative projects. The product combines in a synergistic way the soil moisture retrievals from four passive (SMMR, SSM/I, TMI, and AMSR-E) and two active (ERS AMI and ASCAT) coarse resolution microwave sensors into a global data set spanning the period 1979-2010. The evaluation uses ground-based soil moisture observations of 596 sites from 28 historical and active monitoring networks worldwide. Besides providing conventional measures of agreement, we use the triple collocation technique to assess random errors in the data set. The average Spearman correlation coefficient between ECV_SM and all in-situ observations is 0.46 for the absolute values and 0.36 for the soil moisture anomalies, but differences between networks and time periods are very large. Unbiased root-mean-square differences and triple collocation errors show less variation between networks, with average values around 0.05 and 0.04 m(3) m(-3), respectively. The ECV_SM quality shows an upward trend over time, but a consistent decrease of all performance metrics is observed for the period 2007-2010. Comparing the skill of the merged product with the skill of the individual input products shows that the merged product has a similar or better performance than the individual input products, except with regard to the ASCAT product, compared to which the performance of ECV_SM is inferior. The cause of the latter is most likely a combination of the mismatch in sampling time between the satellite observations and in-situ measurements, and the resampling and scaling strategy used to integrate the ASCAT product into ECV_SM on the other. The results of this study will be used to further improve the scaling and merging algorithms for future product updates. (C) 2014 Elsevier Inc. All rights reserved.