【作者】 陈玲；

【导师】 王根绪；

【作者基本信息】 兰州大学 ， 水文学及水资源， 2007， 硕士

【摘要】 地表蒸散是地气水分循环过程中的重要环节，在地球的大气圈—水圈—生物圈中发挥着重要的作用。合理准确地估算蒸散发，对了解大范围内水分循环和能量平衡具有重要意义。遥感以其能够用少量的地面数据估算大范围区域蒸散的优势被认为是可以经济有效地提供区域和全球实际蒸散发消耗量的唯一方法。本文对原SEBAL模型进行部分改进，结合高分辨率遥感数据Landsat TM估算长江源左冒西孔曲流域的日蒸散量。同时，拟合了关键地形因子、地表参数与蒸散的相关关系，分析了日蒸散对地面输入参数和部分地表参数的敏感性。利用统计资料与同期Lysimeter实测数据，验证了模型在研究区的可行性；将改进前后模型进行对比分析，认为优化后的SEBAL模型估算精度更高。研究区能量通量均值分别为：净辐射673.6W／m²；土壤热通量80.5W／m²；显热通量167.6W／m²；潜热通量425.5W／m²，蒸发比率均值达0.715，可知研究区该时段地气能量交换方式以潜热为主。通过蒸发比率不变法推算出日蒸散，区域均值为6.27mm。通过分析地形因子（坡度、坡向）与蒸散的相关关系，认为运算结果能够准确地反映区域水热空间格局，进一步验证了模型的合理性。关键地表参数中，与蒸散呈正相关的依次为：地表比辐射率（ε_s）、植被覆盖度（f_c）、NDVI、地表粗糙度(z_om)；呈负相关的依次为：地表温度（T_s）、大气短波透射率(τ_sw)，地表反照率（α）。分析日蒸散对地表粗糙度z_om、200米高度处风速u₂₀₀、地表比辐射率ε_s以及大气短波透射率τ_sw等四个参数的敏感性，得知日蒸散对模型中两个地面输入参数(z_om、u₂₀₀)敏感性较低，两者在数值上增大或减小20％，日蒸散几乎不发生变化；蒸散对地表比辐射率ε_s和大气透射率τ_sw敏感程度较高，地表比辐射率与大气短波透射率变化3％，日蒸散区域均值分别变化约10％与4.4％。故建议选择公认精度较高的关键参数反演方法或对经验公式进行区域优化。基于本文研究，提出蒸散发遥感研究的重点应为发展既遵循生物物理机理，又简便易行且能充分考虑区域下垫面非均匀性尺度问题的模型。更多还原

【Abstract】 As a very important part of the water circulation, Evapotranspiration (ET) plays a key role in the process of atmosphere, hydrosphere and biosphere.Estimating it correctly is very important for understanding large-scale energy and water balance. Among the several ET estimation methods, the remote sensing method is regarded as the only technology that can efficiently and economically provide regional and global coverage of actual water consumption.This study refines the original SEBAL algorithm, using the high resolution remote image Landsat TM, and estimates the day ET of Zuomaoxikong watershed in the source region of Yangtze river. Also fits the relation between some surface parameters, terrain factors and day ET ,and analyses the sensitivity of day ET to some parameters which either calculated by ground data or by experimental equations.In the original SEBAL model, the air transmittance was determined by a trial and error method using calculated albedo as an index. For this study, an elevation based transmittance equation was considered. The original SEBAL was limited to flat surfaces. A method of extending it to sloped surfaces, by using DEM information was developed.After validated the estimation results by some statistical information and Lysimeter measured ET, we consider that the developed SEBAL model can operate correctly in the study area and the ET results can imply the heat and vapor spatial pattern of this area accurately.The main conclusions of this dissertation are as follow:The average values of every portion of regional energy balance are: 673.6 W/m~2 for net radiation; 80.5 W/m~2 for soil heat flux; 167.6 W/m~2 for sensible heat flux; and 425.5 W/m~2 for the latent heat flux. The regional average value of Evapotranspiration Fraction reaches to 0.715, which is high enough to imply that the net radiation in the study area is mainly redistributed in latent heat flux at that certain time.Among those several key parameters, four of them have positive correlation with ET. They are surface emissivity, vegetation fraction, NDVI and surface roughness in sequence. Three parameters have negative correlations with ET, which are surface temperature, shortwave transmittance, and surface albedo.This study analyzed the sensitivity of ET to four parameters which are surface roughness, wind speed at 200 meters, surface emissivity and shortwave transmittance. For the change of the former two parameters (surface roughness and wind speed), ET almost has no sensitivity, which indicate that certain trial error of these two parameters will not affect the result of ET. But different phenomena appeared about the other two parameters, 3% change in emissivity and shortwave transmittance can cause 10% and 4.4% change in ET respectively. This means that we should be careful when we choose the equations for the latter two parameters.Based on our research, we should realize that an operational ET estimation model, which is physical-based and also resolve the scale-up problem, is very needed in the future.更多还原