Earth Observations-Based Evapotranspiration in Northeastern Thailand
Earth Observations-Based Evapotranspiration in Northeastern Thailand
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DOI：
10.3390/rs11020138
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发表时间：
2019-01
期刊：
影响因子：
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通讯作者：
Chaolei Zheng;L. Jia;G. Hu;Jing Lu
中科院分区：
文献类型：
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作者：
Chaolei Zheng;L. Jia;G. Hu;Jing Lu
泰国的特点是典型的热带季风气候，并正在遭受严重的水有关的问题，包括季节性干旱和洪水。这些问题与水文过程密切相关，例如，降水和蒸散量（ET），这有助于理解和科普这些问题。研究泰国蒸散量的时空分布规律对当地水资源管理具有重要意义。在目前的研究中，每日ET估计泰国ETMonitor，一个基于过程的模型，主要是卫星地球观测数据集作为输入。ETMonitor算法的一个主要优点是，它引入了土壤水分对ET的影响，通过同化从微波遥感的表层土壤水分，它减少了对地表温度的依赖，因为热遥感是高度敏感的云，这限制了实现每日ET的空间和时间连续性的能力。在本研究中，进一步改进了ETMonitor算法，以利用热遥感。在改进方案中，首先采用陆面温度-植被指数三角形法计算蒸发量，然后利用该方法估算晴天蒸散量。定义了土壤水分胁迫指数（SMSI）来表达土壤水分对蒸散量的约束，并根据估算的晴空蒸散量反演晴空SMSI。然后将晴天SMSI插值到阴天，以获得所有天空条件的SMSI。最后，时间序列ET在日常分辨率实现使用插值时空连续SMSI。在估计的每日ET和通量塔观测值之间发现了良好的一致性，均方根误差在1.08和1.58 mm d−1之间，这表明比中分辨率成像光谱仪（MODIS）的ET产品更准确，特别是对于森林站点。选择位于泰国东北部的智河和门河流域，分析ET的空间格局。结果表明，蒸散量的季节变化波动较大，主要受季风气候的影响。
Thailand is characterized by typical tropical monsoon climate, and is suffering serious water related problems, including seasonal drought and flooding. These issues are highly related to the hydrological processes, e.g., precipitation and evapotranspiration (ET), which are helpful to understand and cope with these problems. It is critical to study the spatiotemporal pattern of ET in Thailand to support the local water resource management. In the current study, daily ET was estimated over Thailand by ETMonitor, a process-based model, with mainly satellite earth observation datasets as input. One major advantage of the ETMonitor algorithm is that it introduces the impact of soil moisture on ET by assimilating the surface soil moisture from microwave remote sensing, and it reduces the dependence on land surface temperature, as the thermal remote sensing is highly sensitive to cloud, which limits the ability to achieve spatial and temporal continuity of daily ET. The ETMonitor algorithm was further improved in current study to take advantage of thermal remote sensing. In the improved scheme, the evaporation fraction was first obtained by land surface temperature—vegetation index triangle method, which was used to estimate ET in the clear days. The soil moisture stress index (SMSI) was defined to express the constrain of soil moisture on ET, and clear sky SMSI was retrieved according to the estimated clear sky ET. Clear sky SMSI was then interpolated to cloudy days to obtain the SMSI for all sky conditions. Finally, time-series ET at daily resolution was achieved using the interpolated spatio-temporal continuous SMSI. Good agreements were found between the estimated daily ET and flux tower observations with root mean square error ranging between 1.08 and 1.58 mm d−1, which showed better accuracy than the ET product from MODerate resolution Imaging Spectroradiometer (MODIS), especially for the forest sites. Chi and Mun river basins, located in Northeast Thailand, were selected to analyze the spatial pattern of ET. The results indicate that the ET had large fluctuation in seasonal variation, which is predominantly impacted by the monsoon climate.