Abstract The NASA L-Band Soil Moisture Active Passive (SMAP) satellite mission launched in 2015 has produced soil moisture and freeze thaw (FT) products at a global scale. While the use of L-band (1.41 GHz) passive microwave radiometry (P-MW) has proven useful in detecting changes in the surface FT state, these classifications have not been comprehensively assessed against similar existing FT products, such as the global FT record from the Special Sensor Microwave/Imager (SSM/I, Ka-band, 37.0 GHz) as part of the FT Earth System Data Record (FT-ESDR). In order to fill in this gap, this study investigates regions in which FT classifications diverge and identifies potential sources of classification variability. The SMAP and SSM/I FT records are compared over an extended period covering multiple seasonal cycles from April 2015 through December 2017. The spatially and temporally varying relationship between these products is examined in relation to climate (Koppen-Geiger climate classes and air temperature), MODIS (MoDerate Resolution Imaging Spectrometer) land cover, and topography (using Global Multi-resolution Terrain Elevation Data). SMAP and SSM/I FT product agreement proportion (Ap) was corrected for seasonality and then separated by land cover classes and compared to the global Ap mean. The agreement between these products vary most notably during freeze and thaw onset and in areas near abundant surface water, snow and ice, and wetlands. Relative to other vegetation types, reduced agreement between FT products is also observed over grasslands, sparsely vegetated lands, as well as mixed and evergreen forests. Distinct seasonal differences in FT classification agreement were also detected between products over cold arid regions and between continental and temperate classes. Similarly, as topographic complexity increases, a decreasing trend in agreement between L- and Ka-band FT products is observed. While reiterating challenges in FT classifications identified by prior studies, this work also contributes new insights by providing detailed geospatial and seasonal analyses into the factors contributing to FT product divergence.

中文翻译：

---

比较全球被动微波冻结/解冻记录：调查 Ka 和 L 波段产品之间的差异

摘要 NASA 于 2015 年发射的 L 波段土壤水分主动被动 (SMAP) 卫星任务在全球范围内产生了土壤水分和冻融 (FT) 产品。虽然 L 波段 (1.41 GHz) 无源微波辐射测量 (P-MW) 的使用已被证明可用于检测表面 FT 状态的变化，但尚未针对类似的现有 FT 产品（例如全球 FT 记录）对这些分类进行全面评估来自特殊传感器微波/成像仪（SSM/I，Ka 波段，37.0 GHz），作为 FT 地球系统数据记录 (FT-ESDR) 的一部分。为了填补这一空白，本研究调查了 FT 分类出现分歧的区域，并确定了分类变异的潜在来源。SMAP 和 SSM/I FT 记录在涵盖 2015 年 4 月至 2017 年 12 月的多个季节性周期的较长时期内进行比较。这些产品之间的空间和时间变化关系在气候（Koppen-Geiger 气候等级和气温）、MODIS（MoDerate 分辨率成像光谱仪）土地覆盖和地形（使用全球多分辨率地形高程数据）方面进行了检查。SMAP 和 SSM/I FT 产品一致性比例 (Ap) 针对季节性进行校正，然后按土地覆盖类别进行分离，并与全球 Ap 平均值进行比较。这些产品之间的一致性在冻结和解冻开始期间以及在靠近丰富的地表水、冰雪和湿地的地区变化最为显着。相对于其他植被类型，在草地、植被稀疏的土地以及混交林和常绿林上也观察到 FT 产品之间的一致性降低。在寒冷干旱地区的产品之间以及大陆和温带类别之间也检测到 FT 分类一致性的明显季节性差异。同样，随着地形复杂性的增加，观察到 L 和 Ka 波段 FT 产品之间的一致性下降趋势。在重申先前研究确定的 FT 分类中的挑战的同时，这项工作还通过对导致 FT 产品差异的因素提供详细的地理空间和季节性分析来提供新的见解。