Mapping Actual Evapotranspiration by Combining Landsat TM and NOAA-AVHRR Images: Application to the Barrax Area, Albacete, Spain

A method that permits determination of actual evapotranspiration, ET, in heterogeneous areas has been proposed. It is based on the relation −B(Ts−Tsm), combines meteorological, National Oceanic and Atmospheric Administration advanced very high resolution radiometer (NOAA-AVHRR), and Landsat thematic mapper (TM) data. Thus, the maximum evapotranspiration for each crop, ETm, is obtained from in situ measurements carried out in a meteorological station; the temperature difference between each pixel and the pixel that has the maximum evapotranspiration, Ts−Tsm, is calculated for each crop from NOAA-AVHRR data; and the crop distribution in the area is known through a Landsat TM image. The semi-empirical coefficient B is derived for each crop in two ways: (1) experimentally and (2) by the identification of crop structure parameters. We have applied the proposed method to the Barrax region, Albacete, whose main crops, maize (Zea mays L.) and barley (Ordeum vulgare L.), cover a 10 km×10 km area. With Penmanʹs method as the standard, a method validation was conducted and an acceptable precision was obtained (±0.8 mm day−1 and ±1.0 mm day−1 for barley and maize, respectively). Finally, actual evapotranspiration images are supplied.