Satellite‐derived surface soil moisture data are available for the Arctic, but detailed validation is still lacking. Previous studies have shown low correlations between in situ and modeled data. It is hypothesized that soil temperature variations after soil thaw impact MetOp ASCAT satellite‐derived surface soil moisture (SSM) measurements in wet tundra environments, as C band backscatter is sensitive to changes in dielectric properties. We compare in situ measurements of water content within the active layer at four sites across the Arctic in Alaska (Barrow, Sagwon, Toolik) and Siberia (Tiksi), taken in the spring after thawing and in autumn prior to freezing. In addition to the long‐term measurement fields, where sensors are installed deeper in the ground, we designed a monitoring setup for measuring moisture very close to the surface in the Lena River Delta, Siberia. The volumetric water content (VWC) and soil temperature sensors were placed in the moss organic layer in order to account for the limited penetration depth of the radar signal. ASCAT SSM variations are generally very small, in line with the low variability of in situ VWC. Short‐term changes after complete thawing of the upper organic layer, however, seem to be mostly influenced by soil temperature. Correlations between SSM and in situ VWC are generally very low, or even negative. Mean standard deviation matching results in a comparably high root‐mean‐square error (on average 11%) for predictions of VWC. Further investigations and measurement networks are needed to clarify factors causing temporal variation of C band backscatter in tundra regions.

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评估苔原环境中 MetOp ASCAT 衍生的表层土壤湿度产品

北极地区可以使用卫星获得的表面土壤湿度数据，但仍缺乏详细的验证。先前的研究表明，现场数据和建模数据之间的相关性较低。假设土壤解冻后的土壤温度变化会影响潮湿苔原环境中 MetOp ASCAT 卫星衍生的表面土壤湿度 (SSM) 测量，因为 C 波段反向散射对介电特性的变化很敏感。我们比较了阿拉斯加（巴罗、萨格旺、图利克）和西伯利亚（提克西）北极四个地点活动层内水含量的原位测量结果，这些测量数据是在春季解冻后和秋季结冰前进行的。除了将传感器安装在地下较深处的长期测量领域之外，我们还设计了一种监测装置，用于测量西伯利亚勒拿河三角洲非常接近地表的湿度。体积含水量（VWC）和土壤温度传感器被放置在苔藓有机层中，以考虑雷达信号的有限穿透深度。ASCAT SSM 变化通常非常小，与原位 VWC 的低变化一致。然而，上层有机层完全解冻后的短期变化似乎主要受土壤温度的影响。SSM 和原位 VWC 之间的相关性通常很低，甚至是负相关。平均标准差匹配导致 VWC 预测出现相对较高的均方根误差（平均 11%）。需要进一步的调查和测量网络来阐明导致苔原地区 C 波段反向散射时间变化的因素。