全天候区域地表蒸散发反演——以黑河流域为例

Retrieval of all-sky surface evapotranspiration in regional scale：acase study over the Heihe River Basin

关键词:  蒸散发  MODIS  CLDAS  逐像元  Penman-Monteith 模型

Key words:  evapotranspiration  MODIS  CLDAS  pixel-to-pixel  Penman-Monteith

摘要:

【目的】蒸散发是生物圈、岩石圈、水圈、冰雪圈和大气圈中水分循环和能量传输 的重要控制因素。为克服区域尺度方法的主观性和站点尺度方法难以反映气象因子空间 异质性的局限，文章以中国境内黑河流域为研究区域，使用2012 年6 月1 日至9 月15 日 的MODIS 数据与CLDAS 格网气象数据探索区域尺度全天候蒸散发遥感反演。【方法】该 文利用逐像元地表温度—植被指数特征空间方法和Penman-Monteith 公式分别估算晴空 像元和有云像元的地表蒸散发，实现了区域尺度全天候蒸散发遥感反演。在分析研究区 CLDAS 气象数据的精度基础之上，利用MODIS 数据反演的短波辐射来替代CLDAS 气象 数据中的短波辐射，作为全天候地表蒸散发的输入参数。最后，利用黑河流域4 个不同站 点实测的地表蒸散发数据对反演值进行验证。【结果】利用MODIS 短波辐射代替CLDAS 气象数据中的短波辐射，能够显著提高蒸散发的反演精度，4 个站点反演值与实测值之 间的平均均方根误差为76.3 W/m2。【结论】利用MODIS 数据和CLDAS 数据可以获得区 域尺度的全天候蒸散发。在缺乏短波辐射数据或短波辐射数据精度较低的情况下，利用 MODIS 数据反演得到的短波辐射作为蒸散发模型的参数输入，能较大地提高蒸散发的反演 精度。

Abstract:

［Purpose］Evapotranspiration（ET）is an important controlling factor for water circulation and energy transfer in the biosphere，lithosphere，hydrosphere，cryosphere and atmosphere. In order to overcome the subjectivity of regional-scale methods and the limitation of site-scale methods that it difficult to reflect the spatial heterogeneity of meteorological factors，the Heihe river basin in China was selected as the study area. The MODIS（Moderate-resolution Imaging Spectroradiometer）data and CLDAS（CMA Land Data Assimilation System）gridded meteorological data from June 1，2012 to September 15，2012 were used to obtain ET over the study area.［Method］In this paper，ET over clear-sky pixels was estimated from a pixel-topixel land surface temperature/vegetation index feature space method. For cloudy pixels，the Penman-Monteith equation was used to calculate ET. Based on the study of the accuracy of the CLDAS meteorological data in the study area，short-wave radiation from the MODIS data is used to replace the short-wave radiation in the CLDAS meteorological data as an input parameter for all-sky ET model. Finally，the measured ET data from four sites in the study area was used to verify the estimated ET.［Result］The results show that using MODIS short-wave radiation to replace that of the CLDAS data can significantly improve the accuracy of ET estimation. The average root mean square error between four sites is 76.3 W/m2.［Conclusion］This study shows that all-sky ET at regional scale can be obtained from MODIS and CLDAS data. For the areas without measurements of solar radiation or the measurements are with low accuracy，taking the MODIS-derived short-wave radiation as an input of the model can significantly improve the accuracy of ET estimation.