Abstract

In order to verify the applicability of different triangular methods for evapotranspiration (ET) estimation and the effect of spatial resolution on triangular methods, the applicability of normalized-difference vegetation index-land surface temperature (NDVI-LST) and NDVI-albedo triangular methods was validated based on the enhanced thematic mapper (ETM)+ moderate-resolution imaging spectrometer (MODIS) data. Considering the effecting of soil moisture on ET, a new triangular method was developed by using the perpendicular drought index (PDI). Compared to the measured values, the result showed that LSTs retrieved by a single-channel method using ETM+ data were closed to the measured values, with a root-mean-square error (RMSE) of 5.7 K. Given the inhomogeneity of the underlying surface, the remote-sensing data related to the low spatial resolution blur the between-pixel differences. A higher spatial resolution of the remote sensing (RS) data corresponds to a greater homogeneity of the distribution of scatter plots in the eigenspace and greater differences between pixels, particularly in the NDVI-LST eigenspace. The eigenspace formed by the PDI and the NDVI possess distinct triangular characteristics, particularly the inversion results of the ETM+ data, with an mean absolute percent error of 14% and an RMSE of 103 W·m−2 . The dry-edge slope introduced by the PDI in the expression increases the accuracy of the estimated ET. Compared to the measured data, the RMSEs of ET estimated by the NDVI-PDI using the ETM+ and MODIS data were reduced to 92 and 121 W⋅m−2, respectively. The regional distribution of ET inverted by the NDVI-PDI method significantly coincided with the actual scenario of the underlying surface.

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