title: A review of current methodologies for regional evapotranspiration estimation from remotely sensed data.
abstract: An overview of the commonly applied evapotranspiration (ET) models using remotely sensed data is given to provide insight into the estimation of ET on a regional scale from satellite data. Generally, these models vary greatly in inputs, main assumptions and accuracy of results, etc. Besides the generally used remotely sensed multi-spectral data from visible to thermal infrared bands, most remotely sensed ET models, from simplified equations models to the more complex physically based two-source energy balance models, must rely to a certain degree on ground-based auxiliary measurements in order to derive the turbulent heat fluxes on a regional scale. We discuss the main inputs, assumptions, theories, advantages and drawbacks of each model. Moreover, approaches to the extrapolation of instantaneous ET to the daily values are also briefly presented. In the final part, both associated problems and future trends regarding these remotely sensed ET models were analyzed to objectively show the limitations and promising aspects of the estimation of regional ET based on remotely sensed data and ground-based measurements.
authors.affiliation: Institute of Geographic Sciences and Natural Resources Research, Beijing 100101, China; E-Mails:  trl_wd@163.com  (R.T.);  zhouch@lreis.ac.cn  (C.H.Z.);  tangbh@igsnrr.ac.cn  (B.H.T.).
authors.forename: Zhao-Liang
authors.initials: ZL
authors.lastname: Li
authors.forename: Ronglin
authors.initials: R
authors.lastname: Tang
authors.forename: Zhengming
authors.initials: Z
authors.lastname: Wan
authors.forename: Yuyun
authors.initials: Y
authors.lastname: Bi
authors.forename: Chenghu
authors.initials: C
authors.lastname: Zhou
authors.forename: Bohui
authors.initials: B
authors.lastname: Tang
authors.forename: Guangjian
authors.initials: G
authors.lastname: Yan
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Zhang