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Remote Sens. 2015, 7(9), 11183-11201; doi:10.3390/rs70911183

Evaluation of Water Use Efficiency Derived from MODIS Products against Eddy Variance Measurements in China

1
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
2
Atmospheric Science, College of Agronomy, Shenyang Agricultural University, Shenyang 110866, China
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editors: Xin Li and Prasad S. Thenkabail
Received: 31 March 2015 / Revised: 24 August 2015 / Accepted: 26 August 2015 / Published: 31 August 2015
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Abstract

Water use efficiency (WUE) is a useful indicator to illustrate the interaction of carbon and water cycles in terrestrial ecosystems. MODIS gross primary production (GPP) and evapotranspiration (ET) products have been used to analyze the spatial and temporal patterns of WUE and their relationships with environmental factors at regional and global scales. Although MODIS GPP and ET products have been evaluated using eddy covariance flux measurements, the accuracy of WUE estimated from MODIS products has not been well quantified. In this paper, we evaluated WUE estimated from MODIS GPP and ET products against eddy covariance measurements of GPP and ET during 2003–2008 at eight sites of the Chinese flux observation and research network (ChinaFLUX) and conducted sensitivity analysis to investigate the possible key contributors to the bias of MODIS products. Results show that MODIS products underestimate eight-day water use efficiency in four forest ecosystems and one cropland ecosystem with the bias from −0.36–−2.28 g·C·kg1 H2O, while overestimating it in three grassland ecosystems with the bias from 0.26–1.11 g·C·kg1 H2O. Mean annual WUE was underestimated by 14%–54% at four forest sites, 45% at one cropland site and 7% at an alpine grassland site, but overestimated by 66% and 9% at a temperate grassland site and an alpine meadow site, respectively. The underestimation of WUE by MODIS data results from underestimated GPP and overestimated ET at four forest sites, while MODIS WUE values are significantly overvalued mainly due to underestimated ET in the three grassland ecosystems. The maximum light use efficiency and fraction of photosynthetically-active radiation (FPAR) were the two most sensitive factors to the estimation of WUE derived from the MODIS GPP and ET algorithms. The error in meteorological data partly caused the overestimation of ET and accordingly underestimation in WUE in subtropical and tropical forests. The bias of MODIS-produced WUE was also derived from the uncertainties in eddy flux data due to gap-filling processes and unbalanced surface energy issue. Their contributions to the uncertainty in estimated WUE at both eight-day and annual scales still need to be further quantified. View Full-Text
Keywords: remote sensing products; validation; ChinaFLUX; water use efficiency remote sensing products; validation; ChinaFLUX; water use efficiency
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Zhang, L.; Tian, J.; He, H.; Ren, X.; Sun, X.; Yu, G.; Lu, Q.; Lv, L. Evaluation of Water Use Efficiency Derived from MODIS Products against Eddy Variance Measurements in China. Remote Sens. 2015, 7, 11183-11201.

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