Estimation of Penetration Depth from Soil Effective Temperature in Microwave Radiometry
Estimation of Penetration Depth from Soil Effective Temperature in Microwave Radiometry
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微波辐射测量中根据土壤有效温度估算穿透深度
DOI：
10.3390/rs10040519
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发表时间：
2018-04-01
期刊：
影响因子：
5
通讯作者：
Su, Zhongbo
中科院分区：
文献类型：
--
作者：
Lv, Shaoning;Zeng, Yijian;Su, Zhongbo
土壤湿度是地球表面模拟中的一个重要变量。两个专门的卫星任务，土壤水分和海洋盐度（SMOS）和土壤水分主动被动（SMAP），目前正在运行，以绘制全球土壤水分分布图。但在这些卫星较长的L波段波长处，由于未知的更深穿透深度，陆地的发射行为变得非常复杂。这种复杂性给卫星土壤水分产品的标定和验证及其应用带来了较大的不确定性。在零阶非相干微波辐射传输模型框架中，土壤有效温度是唯一包含深度信息的分量，从而为量化穿透深度提供了必要的联系。本文采用多层土壤有效温度（Lv's Teff）方案，确定了穿透深度与土壤有效温度之间的关系，并与玛曲测网的实测资料进行了对比验证。研究结果表明，在土壤温度沿光学深度沿着呈线性梯度分布的条件下，穿透深度可根据Lv的Teff格式估算;反之，在相同的线性假设下，穿透深度处的土壤温度应等于土壤有效温度。这种推断的准确性取决于线性土壤温度梯度的假设在多大程度上得到满足。本研究的结果将有助于加深对SMOS和SMAP反演土壤水分产品的认识，提高资料同化和气候研究的技术水平。
Soil moisture is an essential variable in Earth surface modeling. Two dedicated satellite missions, the Soil Moisture and Ocean Salinity (SMOS) and the Soil Moisture Active Passive (SMAP), are currently in operation to map the global distribution of soil moisture. However, at the longer L- band wavelength of these satellites, the emitting behavior of the land becomes very complex due to the unknown deeper penetration depth. This complexity leads to more uncertainty in calibration and validation of satellite soil moisture product and their applications. In the framework of zeroth- order incoherent microwave radiative transfer model, the soil effective temperature is the only component that contains depth information and thus provides the necessary link to quantify the penetration depth. By means of the multi- layer soil effective temperature (Lv's Teff) scheme, we have determined the relationship between the penetration depth and soil effective temperature and verified it against field observations at the Maqu Network. The key findings are that the penetration depth can be estimated according to Lv's Teff scheme with the assumption of linear soil temperature gradient along the optical depth; and conversely, the soil temperature at the penetration depth should be equal to the soil effective temperature with the same linear assumption. The accuracy of this inference depends on to what extent the assumption of linear soil temperature gradient is satisfied. The result of this study is expected to advance understanding of the soil moisture products retrieved by SMOS and SMAP and improve the techniques in data assimilation and climate research.