Evaluation of Algorithms to estimate Daily Evapotranspiration from Instantaneous Measurements under All-sky Conditions

35th International Symposium on Remote Sensing of Environment

地球科学;生态环境科学

Ruan, Zhaojie^1 ; Jia, Li^1,2 ; Menenti, Massimo^3

State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China^1

Alterra, Wageningen University and Research Centre, Wageningen, Netherlands^2

Delft University of Technology, Delft, Netherlands^3

关键词: Agricultural crops;    Daily evapotranspirations;    Evaporative fraction;    Instantaneous measurement;    Northwestern China;    Polar-orbiting satellites;    Sinusoidal functions;    Water resources assessment;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/17/1/012133/pdf
DOI  :  10.1088/1755-1315/17/1/012133

学科分类：环境科学（综合）

来源: IOP

【 摘 要 】

Instantaneous EvapoTranspiration (ET) can be estimated using a single set of instantaneous observations by polar orbiting satellites during the day. Daily, weekly or monthly total ET is required for hydrological studies and water resources assessment. This requires daily total ET regardless of cloud cover. The daily total ET is usually determined assuming that the evaporative fraction (EF) remains constant during at least the central hours of the day and that the product of EF times the daily total net radiation gives a satisfactory estimate of daily total ET. The impact of cloud cover is rarely discussed. In this paper, we used data collected at two experimental sites in the Heihe River basin in northwestern China: Arou with grassland in an alpine region and Yingke with agricultural crops in a semi-arid region. Two methods were evaluated to determine daily total ET with instantaneous observations: a) self-conservation of evaporative fraction (EF-const); b) assuming the diurnal course of ET is the same sinusoidal function of the time of the instantaneous observation as the solar irradiance (Rs) (ET-Rs). Daily ET calculated with the two methods were evaluated against observed daily values. The results showed that these assumptions did not hold and the accuracy of ET estimates obtained with either method was reduced by: a) diurnal variation of ET and b) the time lag between ET and net radiation under clear skies. Larger errors occurred when applying both methods under cloudy conditions during the growing season, while in the remaining part of the year the impact of cloud cover was lower.