Improving spatial resolution of ET seasonal for irrigated rice in Zhanghe, China

Recently, advances have been made to obtain estimates of evapotranspir ation (ET) through remote sensing. A problem still persists to get ET over a longer time period. Orbiting satellites supply with images answering the need for water consumption data, but due to technical limitations have either high spatial resolution restricted to low revisit frequency, or frequent revisit cycle but low spatial resolution. Remote sensing technicians are facing this problem when trying to provide regular and fine resolution information about water consumption of crops in irrigation systems. The solution would be to combine the high spatial resolution with the high temporal resolution satellite images. In this study, actual evapotranspiration images from NOAA AVHRR acquired at various dates in Zhanghe irrigation district are used together with meteorological daily reference evapotranspiration data to simulate daily evapotranspiration. A temporal integration for the May – September rice cropping season provides the seasonal actual evapotranspiration map. This information, collected at a pixel size of 1.1 km is merged together with a Landsat 7 ETM+ image acquired at a strategic moment of the cropping season. The result is a more detailed redistribution of seasonal evapotranspiration to finer resolutions, while keeping the actual evapotranspirated global volume constant, before and after the merging. This provides a better located estimation of water consumption, especially for rice. Irrigated rice fields are of particular interest to the water managers, since these fields are the main cash crop of the irrigation district. In the discussion that follows, it is shown that the remote sensing limitations can be overcome using meteorological data and combined information from two satellites, providing detailed results of low cost.