Soil moisture (SM) is a key variable in hydrological processes, bio-ecological processes, and biogeochemical processes. Long-term observations of soil moisture over large areas are critical to research on flooding and drought monitoring, water resource management, and crop yield forecasts. In this paper, Fengyun (FY3B and FY3C) SM products, Japan Aerospace Exploration Agency (JAXA) SM products from the Advanced Microwave Scanning Radiometer 2 (AMSR2), the Land Parameter Retrieval Model (LPRM) AMSR2 L3 SM products, the Version 2 (v2) global land parameter data record (LPDR) of SM products, Soil Moisture Ocean Salinity (SMOS) Centre Aval de Traitement des Données SMOS (CATDS) L3 SM products, the Soil Moisture Active Passive (SMAP) passive L3 SM products and the European Space Agency(ESA) Climate Change Initiative (CCI) SM products were evaluated using the ground-based observations in the Little Washita, Fort Cobb and Yanco networks. Long-time series comparison between measured and satellite products was conducted to evaluate the overall performance of FY3 series satellites SM products. Bias (mean bias), R (correlation coefficient), RMSE (root mean square error) and ubRMSE (unbiased root mean square error) were calculated to explore the agreement between satellite products and in-situ measurements. Taylor diagrams were used to compare the performance of various satellite products. The result showed that (1) FY3B, FY3C and LPRM AMSR2 ascending and descending products had an obvious overestimate with in-situ soil moisture in three networks. (2) JAXA AMSR2 ascending and descending products had considerable underestimation in three networks. (3) The validation result of SMOS ascending and descending products over the three networks was satisfactory, with a rather high correlation than other X-band products. (4) The validation result of SMAP ascending and descending products outperformed the other products over the Little Washita and Fort Cobb networks. (5) The ESA CCI product had the lowest values of RMSE and ubRMSE than the other products in the Yanco network, revealing the effectiveness of merging active and passive soil moisture products. (6)The LPDR descending SM products had better performance than the LPDR ascending SM products in the LW and FC networks.

中文翻译：

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通过三个密集网络对遥感土壤水分产品和地面观测进行评估

土壤水分（SM）是水文过程，生物生态过程和生物地球化学过程中的关键变量。对大面积土壤湿度的长期观测对于洪水和干旱监测，水资源管理以及作物产量预报的研究至关重要。本文中的风云（FY3B和FY3C）SM产品，日本航空航天局（JAXA）SM产品来自高级微波扫描辐射计2（AMSR2），陆地参数检索模型（LPRM）AMSR2 L3 SM产品，版本2（ v2）SM产品的全球土地参数数据记录（LPDR），土壤水分海洋盐度（SMOS）特纳尼特·唐内斯（CDS）L3 SM产品中心，使用Little Washita，Fort Cobb和Yanco网络中的地面观测资料对土壤水分主动被动（SMAP）被动L3 SM产品和欧洲航天局（ESA）气候变化倡议（CCI）SM产品进行了评估。进行了实测和卫星产品之间的长期系列比较，以评估FY3系列卫星SM产品的整体性能。计算了偏差（平均偏差），R（相关系数），RMSE（均方根误差）和ubRMSE（无均方根误差），以探索卫星产品与现场测量之间的一致性。泰勒图用于比较各种卫星产品的性能。结果表明：（1）FY3B，在三个网络中，FY3C和LPRM AMSR2的上升和下降产物对原位土壤水分都有明显的高估。（2）JAXA AMSR2的上升和下降产品在三个网络中均被低估了。（3）SMOS上升和下降乘积的验证结果这三个网络上的s令人满意，与其他X波段产品相比具有很高的相关性。（4）在Little Washita和Fort Cobb网络上，SMAP上升和下降产品的验证结果优于其他产品。（5）与Yanco网络中的其他产品相比，ESA CCI产品的RMSE和ubRMSE值最低，这显示了合并主动和被动土壤水分产品的有效性。（6）在LW和FC网络中，LPDR下降SM产品的性能优于LPDR上升SM产品。