Abstract A field campaign was conducted October 30th to November 13th, 2015 with the intention of capturing diurnal soil freeze/thaw state at multiple scales using ground measurements and remote sensing measurements. On four of the five sampling days, we observed a significant difference between morning (frozen scenario) and afternoon (thawed scenario) ground-based measurements of the soil relative permittivity. These results were supported by an in situ soil moisture and temperature network (installed at the scale of a spaceborne passive microwave pixel) which indicated surface soil temperatures fell below 0 °C for the same four sampling dates. Ground-based radiometers appeared to be highly sensitive to F/T conditions of the very surface of the soil and indicated normalized polarization index (NPR) values that were below the defined freezing values during the morning sampling period on all sampling dates. The Scanning L-band Active Passive (SLAP) instrumentation, flown over the study region, showed very good agreement with the ground-based radiometers, with freezing states observed on all four days that the airborne observations covered the fields with ground-based radiometers. The Soil Moisture Active Passive (SMAP) satellite had morning overpasses on three of the sampling days, and indicated frozen conditions on two of those days. It was found that >60% of the in situ network had to indicate surface temperatures below 0 °C before SMAP indicated freezing conditions. This was also true of the SLAP radiometer measurements. The SMAP, SLAP and ground-based radiometer measurements all indicated freezing conditions when soil temperature sensors installed at 5 cm depth were not frozen.

中文翻译：

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通过遥感和地面观测捕捉农业土壤冻融状态：土壤冻融验证活动

摘要 2015 年 10 月 30 日至 11 月 13 日进行了一次实地活动，目的是使用地面测量和遥感测量在多个尺度上捕获昼夜土壤冻融状态。在五个采样日中的四个日中，我们观察到土壤相对介电常数的早晨（冻结情景）和下午（解冻情景）地面测量值之间存在显着差异。这些结果得到了原位土壤湿度和温度网络（安装在星载无源微波像素的尺度上）的支持，该网络表明在相同的四个采样日期，地表土壤温度低于 0 °C。地基辐射计似乎对土壤表面的 F/T 条件高度敏感，并在所有采样日期的早晨采样期间指示归一化极化指数 (NPR) 值低于定义的冻结值。在研究区域上空飞行的扫描 L 波段有源无源 (SLAP) 仪器与地基辐射计显示出非常好的一致性，在所有四天都观察到冻结状态，机载观测覆盖了地基辐射计的领域。土壤水分主动被动 (SMAP) 卫星在三个采样日的早晨进行了立交桥，并在其中两天显示了冻结条件。发现在 SMAP 指示冻结条件之前，>60% 的原位网络必须指示低于 0°C 的表面温度。SLAP 辐射计测量也是如此。SMAP、SLAP 和地基辐射计测量结果都表明，当安装在 5 厘米深度的土壤温度传感器未结冰时，会出现结冰情况。