Evaluation of remotely sensed and reanalysis soil moisture products over the Tibetan Plateau using in-situ observations
Evaluation of remotely sensed and reanalysis soil moisture products over the Tibetan Plateau using in-situ observations
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DOI：
10.1016/j.rse.2015.03.008
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发表时间：
2015-06
影响因子：
13.5
通讯作者：
J. Zeng;Zhen Li;Quan Chen;H. Bi;Jianxiu Qiu;Pengfei Zou
中科院分区：
文献类型：
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作者：
J. Zeng;Zhen Li;Quan Chen;H. Bi;Jianxiu Qiu;Pengfei Zou
长期大尺度遥感和再分析青藏高原土壤水分产品对于了解该地区地气相互作用及其对亚洲大陆天气气候的影响具有重要意义。然而，在使用这些产品之前评估其可靠性非常重要。本研究利用代表青藏高原不同气候和植被条件的三个网络的现场土壤湿度测量结果，评估了2002-2012年期间7个遥感土壤湿度产品和1个再分析土壤湿度产品的技术。遥感土壤湿度产品包括源自先进微波扫描辐射计地球观测系统（AMSR-E）的三种广泛使用的产品：美国国家航空航天局（NASA）土壤湿度产品、土地参数反演模型（LPRM）土壤湿度产品和日本宇宙航空研究开发机构（JAXA）土壤湿度产品；其余产品是JAXA AMSR2土壤湿度产品、土壤湿度和海洋盐度（SMOS）土壤湿度产品、高级散射仪（ASCAT）土壤湿度产品和基本气候变量（ECV）土壤湿度产品（ECV）土壤湿度产品是使用主动和被动土壤湿度产品的新合并产品。再分析产品是欧洲中期天气预报中心（ECMWF）制作的最新ERA-Interim产品。结果表明，除了 NASA 产品明显低估土壤湿度且缺乏时间动态之外，所有这些产品总体上都能很好地捕获土壤湿度动态。 JAXA AMSR-E和AMSR2产品在大多数情况下都会低估地面测量结果，而LPRM产品给出的季节性幅度比现场观测大得多，并且具有较大的正偏差。看来SMOS的观测受到众所周知的射频干扰（RFI）的严重影响，导致SMOS产品出现很大的噪声和偏差。 ASCAT 产品高估了地面测量值，但它与原位土壤湿度的相关性非常好，并且受植被覆盖的影响也较小。总体而言，ECV 和 ERA 产品优于其他产品。尽管ECV产品低估了土壤湿度，但它与地面测量值具有最好的相关性，并且很好地捕捉了原位土壤湿度的变化，而ERA产品最接近土壤湿度观测的绝对值。总体而言，大多数产品在植被稀疏地区的相关性方面给出了合理的结果。我们期望验证结果可以作为算法开发人员的反馈，进一步提高青藏高原土壤水分反演的准确性。
Long-term and large-scale remotely sensed and reanalysis soil moisture products of the Tibetan Plateau are very important for understanding the land–atmosphere interactions in this area and their impacts on the weather and climate in the Asian continent. However, it is of great importance to assess the reliability of these products before using them. In the study, in-situ soil moisture measurements from three networks which represent different climatic and vegetation conditions over the Tibetan Plateau are used to evaluate the skill of seven remotely sensed soil moisture products and one reanalysis soil moisture product in the period of 2002–2012. The remotely sensed soil moisture products include three widely used products derived from the Advanced Microwave Scanning Radiometer — Earth Observing System (AMSR-E): the National Aeronautics and Space Administration (NASA) soil moisture product, the Land Parameter Retrieval Model (LPRM) soil moisture product, and the Japan Aerospace Exploration Agency (JAXA) soil moisture product; the remaining products are the JAXA AMSR2 soil moisture product, the Soil Moisture and Ocean Salinity (SMOS) soil moisture product, the Advanced Scatterometer (ASCAT) soil moisture product, and the Essential Climate Variable (ECV) soil moisture product which is a new merged product using both active and passive soil moisture products. The reanalysis product is the latest ERA-Interim product produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The results show that all these products can generally capture the soil moisture dynamics well except for the NASA product which significantly underestimates the soil moisture and also lacks temporal dynamics. The JAXA AMSR-E and AMSR2 products underestimate the ground measurements at most of the time, whereas the LPRM product gives much larger seasonal amplitude than the in-situ observations with a large positive bias. It seems that the SMOS observations are severely affected by the well-known radio-frequency interference (RFI) which leads to a big noise and bias in the SMOS product. The ASCAT product overestimates the ground measurements, but it correlates with in-situ soil moisture very well and is also less influenced by vegetation cover. In general, the ECV and ERA products outperform other products. Though the ECV product underestimates the soil moisture, it shows the best correlation with ground measurements and captures the variation of in-situ soil moisture very well while the ERA product is closest to the absolute values of soil moisture observations. Overall, most of the products give reasonable results in terms of correlation in sparsely vegetated areas. We expect that the validation results can be used as a feedback to the algorithm developers to further enhance the accuracy of soil moisture retrievals over the Tibetan Plateau.