ABSTRACT In this study, a new approach to identify the freeze/thaw states of tundra topsoil was developed based on the polarization ratio index, which was calculated from the reflectivity values of soil. Reflectivity was estimated from radiometric measurements of the SMAP satellite using the values of vertical polarization brightness temperature measured by the AMSR-2 radiometer at 6.9 GHz; this value was used to characterize the effective temperature of the soil. The proposed approach was tested using weather station data on soil surface temperatures for six test sites located in the North Slope of Alaska and the Yamal Peninsula collected from April 2015 to June 2018. The modified polarization ratio index, calculated from values of reflectivity rather than from brightness temperatures, significantly improved the possibility of determining the reference values of the index in the winter and in the summer. During testing, the modified index showed a good correlation between the dates of transition through the threshold level and soil temperature transition through 0ºC, as recorded at meteorological stations.

中文翻译：

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基于结合 SMAP 和 AMSR-2 无线电亮度观测的北极地区土壤冻融状态检测

摘要 在这项研究中，基于极化比率指数开发了一种识别苔原表土冻融状态的新方法，极化比率指数是根据土壤的反射率值计算的。反射率是根据 SMAP 卫星的辐射测量值估算的，使用的是 AMSR-2 辐射计在 6.9 GHz 测量的垂直极化亮温值；该值用于表征土壤的有效温度。使用 2015 年 4 月至 2018 年 6 月收集的位于阿拉斯加北坡和亚马尔半岛的六个测试点的土壤表面温度气象站数据对提议的方法进行了测试。亮度温度，显着提高了确定冬季和夏季指标参考值的可能性。在测试期间，修改后的指数显示出通过阈值水平的过渡日期与通过 0ºC 的土壤温度过渡之间的良好相关性，如气象站记录的那样。