Estimating Paddy Field Evapotranspiration using Remote Sensing Multispectral Images

Recently, efficient monitoring of environmental changes has become a reality with the advancement of remote sensing technology. Among all kinds of environmental monitoring, water resources are main issues that are highly concerned in Taiwan. Although Taiwan’s annual rainfall is abundant, the non-uniform distribution both in space and time result in water shortage problem. Agriculture holds the biggest share of water right, and most water use in agricultural is for irrigation, so the crop evapotranspiration is important to water resource planning in agricultural.
By selecting the paddy rice field in Yilan city as the site of measurement, three methods including FAO Penman-Monteith method, eddy covariance method, and using Landsat ETM+ are used to evaluate the evapotranspiration during spring and summer of 2010 in the research. The part of using multispectral images in the research is combined with the in-situ surface meteorological measurement, such as air temperature and wind velocity, and use remote sensing data to evaluate the net radiation, soil heat flux, and surface conditions, and these parameters are used to estimate evapotranspiration using an energy balance approach. The results of FAO-56 and using Landsat ETM+ are similar to previous studies and different from eddy covariance. It is shown that using multispectral images to evaluate evapotranspiration of paddy rice is feasible.