An artificial neural network approach to estimate evapotranspiration from remote sensing and AmeriFlux data

Abstract

A simple and accurate method to estimate evapotranspiration (ET) is essential for dynamic monitoring of the Earth system at a large scale. In this paper, we developed an artificial neural network (ANN) model forced by remote sensing and AmeriFlux data to estimate ET. First, the ANN was trained with ET measurements made at 13 AmeriFlux sites and land surface products derived from satellite remotely sensed data (normalized difference vegetation index, land surface temperature and surface net radiation) for the period 2002–2006. ET estimated with the ANN was then validated by ET observed at five AmeriFlux sites during the same period. The validation sites covered five different vegetation types and were not involved in the ANN training. The coefficient of determination (R²) value for comparison between estimated and measured ET was 0.77, the root-mean-square error was 0.62 mm/d, and the mean residual was -0.28. The simple model developed in this paper captured the seasonal and interannual variation features of ET on the whole. However, the accuracy of estimated ET depended on the vegetation types, among which estimated ET showed the best result for deciduous broadleaf forest compared to the other four vegetation types.

Keywords

AmeriFlux / artificial neural network (ANN) / evapotranspiration (ET) / remote sensing

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Acknowledgments

This work was supported by Shanghai Science and Technology Committee Program- Special for EXPO (No.10DZ0581600), and the National Basic Research Program of China (No. 2010CB950902) , and the National Natural Science Foundation of China (Grant No.41201358). The flux tower evapotranspiration measurement data were provided by AmeriFlux. We gratefully acknowledge all tower site principle investigators and their teams for providing the evapotranspiration data used in this study. MODIS Vegetation Indexes product and Land Surface Temperature product were obtained from Oak Ridge National Laboratory Distributed Active Archive Center. NASA GEWEX solar radiation data were obtained from the NASA Langley Research Center Atmospheric Science Data Center.

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