地表反照率不同计算方法对干旱区流域蒸散反演结果的影响——以新疆三工河流域为例

地表蒸散是维持地球表面水量平衡和热量平衡的重要环节,SEBAL模型作为一种快速且有效的反演地表蒸散的遥感物理模型方法,在地表蒸散研究中得到广泛应用。地表反照率作为影响地表能量平衡的重要因素,同时也是SEBAL模型的重要输入参数,因此不同的地表反照率计算方法对SEBAL模型的反演结果有重要影响。以新疆三工河流域为研究区,利用Landsat8 OLI/TIRS数据,以应用最为广泛的Smith地表反照率计算法和Liang地表反照率计算法两种方法计算地表反照率,并输入SEBAL模型中反演日蒸散量,比较分析两种地表反照率计算方法对蒸散反演结果的影响,得出以下结论:(1)两种地表反照率计算方法下经SEBAL模型得到的日蒸散量与实测值拟合程度均较高,不同年份下线性拟合决定系数大于0.75,但是使用Smith方法计算出的地表反照率结合SEBAL模型得到的日蒸散量与实测值拟合程度更高;(2)通过RMSE等精度指标比较两种地表反照率计算方法下基于SEBAL模型反演的日蒸散量,结果显示,Smith地表反照率计算方法下反演的日蒸散量精度略高;(3)Smith地表反照率计算方法下最终得到的区域日均蒸散量高于使用Liang地表反照率计算方法最终得到的区域日均蒸散量,夏季差异最大,差异为0.64 mm/d,其他季节差异较小,差异约为0.2 mm/d。(4)进一步比较研究日内两种地表反照率计算方法得到的地表反照率,结果显示,Smith地表反照率计算法得到的地表反照率均值均小于同时期Liang地表反照率计算法得到的地表反照率均值。

Influence of different surface albedo calculation methods on the simulation of evapotranspiration from the Sangong River Basin in the arid region of Xinjiang

Surface evapotranspiration is an important link for maintaining the water and heat balance of the earth. The SEBAL model is a remote sensing evapotranspiration estimation model used widely in the evapotranspiration research field. Surface albedo is not only a significant factor for the surface energy balance but is a vital input parameter in the SEBAL model. Different surface albedo computing methods will affect the results of the SEBAL model. In this study, we used two surface albedo computing methods, which were proposed by Smith Ronald and Liang Shunlin, respectively, to calculate the surface albedo for the Sangong River Basin in Xinjiang. Then, the calculated surface albedo was input into the SEBAL model to obtain a diary surface evapotranspiration. By analyzing two kinds of evapotranspiration and surface albedo results, we were able to draw several conclusions. The diary evapotranspiration results calculated from the two kinds of surface albedo methods and the SEBAL model fit well with the measured values. The smallest coefficient of determination was 0.75. The evapotranspiration results calculated using Smith''s surface albedo showed a higher correlation with the measured diary evapotranspiration value than that of Liang''s surface albedo. We compared the two diary evapotranspiration results using RMSE and other indicators, and we found that the evapotranspiration results from Smith''s albedo method was more accurate than Liang''s. The average diary evapotranspiration using Smith''s surface albedo was higher than that of Liang''s albedo; the difference was greater in the summer than in the other seasons tested (0.64 mm/d). The difference in the other seasons was smaller (0.2 mm/d). An additional comparison of the two kinds of average surface albedo revealed that the average surface albedo calculated by Smith''s method was less than that of Liang''s method for 6 periods.