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 ET=ETm-B(T-s-T-sm), which combines meteorological, National Oceanic an d 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 measu rements carried out in a meteorological station; the temperature diffe rence between each pixel and the pixel that has the maximum evapotrans piration, T-s-T-sm, is calculated for each crop from NOAA-AVHRR data; and the crop distribution in the area is known through a Landsat TM im age. The semi-empirical coefficient B is derived for each crop in two ways: (1) experimentally and (2) by the identification of crop structu re parameters. We have applied the proposed method to the Barrax regio n, Albacete, whose main crops, maize (Zea mays L.) and barley (Ordeum vulgare L.), cover a 10 km x 10 km area. With Penman's method as the s tandard, 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 su pplied. (C) Elsevier Science Inc., 1998.