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摘要： SMOS和SMAP都是为获取全球土壤水分信息而设计的专题卫星，均搭载了L波段辐射计。进行二者的横向对比是构建具有一致性的全球土壤水分数据集的关键基础。虽然SMAP、SMOS名义上的过境时刻是固定的，但二者的实际过境时刻随时间和空间发生变化，它们与地面实测数据三者之间难以匹配形成时序上严格统一的样本对，从而给土壤水分反演结果的精度评定带来困难。针对这一问题，以美国大陆地区为研究区，首先对2016~2017年SMOS、SMAP土壤水分数据的时间戳进行统计，判定二者过境的交叠时段；进而利用高观测频率、大空间尺度的实测数据，研究表层土壤水分在此时段内的自然变化特征。结果显示，按照全部、无降水、有降水3种条件，在样本量分别为98.14%、99.51%和88.49%的绝大多数情况下，表层土壤水分的变化量为0.007 m3/m3、0.007 m3/m3和0.012 m3/m3， 远小于SMOS、SMAP的目标精度（0.04 m3/m3）。初步证实： ①SMOS与SMAP的土壤水分反演结果（L2数据）可进行直接比对;②过境时刻差异对验证误差的影响可不计。 关键词： SMOS;  SMAP;  微波遥感;  表层土壤水分;  土壤水分稳定性     Abstract: SMOS and SMAP are both dedicated to acquire global soil moisture information with L band radiometer. The parallel comparison between them is the key foundation for the integration of a consistent global soil moisture dataset. Though the nominal passing time of SMAP and SMOS are designed fixed, the precise time they move overhead locally may not be the same because of the variation in spatial and temporal, practically it is unable to match SMAP, SMOS and field observations in temporal rigidly, therefore the evaluation on their soil moisture retrievals is hard to carry. Research on this mismatch problem is made in the continental United States; firstly, the overlapping period of the two satellites is determined on the basis of a statistic on the time stamp of 2016~2017 SMOS and SMAP soil moisture data; then, the natural variation characteristics of surface soil moisture within this period is studied using in-situ data which having high density in temporal and large scale in spatial. Results showed that, by grouping the samples in the three conditions of entire, no precipitation and with precipitation, where the sample ratio of 98.14%, 99.51% and 88.49% in each group, respectively, meaning in most cases, the surface soil moisture presents a variation of 0.007 m3/m3, 0.007 m3/m3 and 0.012 m3/m3accordingly, which is far less than the nominal accuracy of SMOS and SMAP (0.04 m3/m3). It can be demonstrated preliminarily, ① the direct comparison of SMOS and SMAP soil moisture retrievals (L2 data) is acceptable, ② validation error induced by the difference of passing time can be neglected.

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