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Open AccessArticle

Regional Daily ET Estimates Based on the Gap-Filling Method of Surface Conductance

by Jiaming Xu 1,2, Bingfang Wu 1,2,*, Nana Yan 1 and Shen Tan 1,2
1
Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Olympic Village Science Park, W. Beichen Road, Beijing 100101, China
2
College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(4), 554; https://doi.org/10.3390/rs10040554
Received: 9 March 2018 / Revised: 22 March 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
(This article belongs to the Special Issue Remote Sensing of Land-Atmosphere Interactions)
Remote sensing allows regional evapotranspiration (ET) values to be obtained. Surface conductance is a key variable in estimating ET and controls surface flux interactions between the underlying surface and atmosphere. Limited by the influence of clouds, ET can only be estimated on cloud-free days. In this study, a gap-filling method is proposed to acquire daily surface conductance, which was coupled into a Penman-Monteith (P-M) equation, to estimate the regional daily ET over the Hai River Basin. The gap-filling method is coupled with the canopy conductance, surface conductance and a simple time extension method, which provides more mechanisms and is more comprehensive. Field observations, including eddy covariance (EC) fluxes and meteorological elements from automatic weather station (AWS), were collected from two sites for calibration and validation. One site is located in Guantao County, which is cropped in a circular pattern with winter wheat and summer maize. The other site is located in Miyun County, which has orchard and summer maize crops. The P-M equation was inverted to the computed surface conductance at the field scale, and latent heat fluxes from EC were processed and converted to daily ET. The results show that the surface conductance model used in the gap-filling method performs well compared with the inverted surface conductance, which suggests that the model used here is reasonable. In addition, the relationship between the results estimated from the gap-filling method and EC measurements is more pronounced than that between the other method and the EC measurements. The R 2 values improve from 0.68 to 0.75 at the Guantao site and from 0.79 to 0.88 at the Miyun site. The improvement mainly occurs during the growing crop season, according to the temporal variations in the results. View Full-Text
Keywords: surface conductance; gap-filling; evapotranspiration (ET); ETWatch; Hai River Basin surface conductance; gap-filling; evapotranspiration (ET); ETWatch; Hai River Basin
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MDPI and ACS Style

Xu, J.; Wu, B.; Yan, N.; Tan, S. Regional Daily ET Estimates Based on the Gap-Filling Method of Surface Conductance. Remote Sens. 2018, 10, 554.

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