Based on the Gaussian Fitting Method to Derive Daily Evapotranspiration from Remotely Sensed Instantaneous Evapotranspiration

Suhua Liu,Hongbo Su,Weimin Wang,Jing Tian,Hong Liang,Renhua Zhang,Shaohui Chen,Lijun Yang

doi:10.1155/2019/6253832

Abstract

Evapotranspiration (ET) is a significant component in the water cycle, and the estimation of it is imperative in water resource management. Regional ET can be derived by using remote sensing technology which combines remote sensing inputs with ground-based measurements. However, instantaneous ET values estimated through remote sensing directly need to be converted into daily totals. In this study, we attempted to retrieve daily ET from remotely sensed instantaneous ET. The study found that the Gaussian fitting curve closely followed the ET measurements during the daytime and hence put forward the Gaussian fitting method to convert the remotely sensed instantaneous ET into daily ETs. The method was applied to the middle reaches of Heihe River in China. Daily ETs on four days were derived and evaluated with ET measurements from the eddy covariance (EC) system. The correlation between daily ET estimates and measurements showed high accuracy, with a coefficient of determination (R2) of 0.82, a mean average error (MAE) of 0.41 mm, and a root mean square error (RMSE) of 0.46 mm. To make more scientific assessments, percent errors were calculated on the estimation accuracy, which ranged from 0% to 18%, with more than 80% of locations having the percent errors within 10%. Analyses on the relationship between daily ET estimates and land use status were also made to assess the Gaussian fitting method, and the results showed that the spatial distribution of daily ET estimates well demonstrated ET differences caused by land use types and was intimately linked with the vegetation pattern. The comparison between the Gaussian fitting method and the sine function method and the ETrF method indicated that results derived through the Gaussian fitting method had higher precision than that obtained by the sine function method and the ETrF method.

Highlights

Evapotranspiration (ET), which is crucial to the hydrological cycle, is defined as the synthesis process of evaporation and transpiration
For EC1 with the vegetable surface, the R2 between the simulations by the Gaussian fitting method and the measurements are higher than 0.9 on most days and the root mean square error (RMSE) are lower than 20 W/m2 on all days
According to the above results, it is obvious that the Gaussian fitting results in June 2012 are quite consistent with the diurnal variation of ET measurements at EC stations, no matter the underlying surface, which means the Gaussian fitting method can describe the diurnal variation of ET accurately and can be used as an approach to simulate daily ET

Summary

Introduction

Evapotranspiration (ET), which is crucial to the hydrological cycle, is defined as the synthesis process of evaporation and transpiration. It is the link of energy and water exchanges among the biosphere, atmosphere, and hydrosphere [1,2,3,4,5]. ET is the largest loss of precipitation, and it is a significant outgoing water flux from the earth’s surface. The amount of ET almost equals that of precipitation [6].

Methods

Results

Discussion

Conclusion