Adv. Space Res. Vol. 9, No. 7, pp. (7)255 (7)258, 1989 (1273 1177/89 $0.00 +.50 Printed in Great Britain. All rights reserved. Copyright © 1989 COSPAR APPLICATION OF THERMAL INFRARED REMOTE SENSING TO THE ESTIMATION OF REGIONAL EVAPOTRANSPIRATION Z. Dunkel,* P. Boz6,** T. Szab6* and V. Vadfisz** *Central Meteorological Institute, P.O. Box 38, H-1525 Budapest, Hungary **Central Institute for Weather Forecasting, P.O. Box 32, H-1675 Budapest, Hungary ABSTRACT Infrared temperatures at varied spatial resolution could be obtatined efficiently and accurately, and therefore, it is important to address its usefulness in estimation of regional evapotranspiration. A comparison of ground measured and satellites determined surface temperatures has been performed in the 1987 summer. The ground measurements were located over nearly homogeneous water and arable crops surfaces to determine the variation of surface tempera- ture. A method has recently been developed to deduce the latent heat flux over active surface from remote sensed temperature. We calculated the evapotranspiration using the energy balance equation substituting the infrared tem- peratures. INTRODUCTION The knowledge of the evapotranspiration is of great importance because of many reasons. First, it is one of the main factors in the water budget. Second, the latent heat is one of the terms of the energy balance equation. Third, the cal- culation of evapotranspiration is of great interest in agricultural practice because it permits the evaluation of the amount of needed irrigation water. This information is important especially in such a country as Hungary where the drougts occur very frequently. In our study we discuss the evaluation of the regional evapotranspiration based on remotely sensed temperature. The possibility of the application of the described method in Hungary has been examined. The ground measurements were carried out in clear weather condition on a 300 hectares wheat-field in west part of Hungary when LANDSAT-5 satellite passed it over. Simultaneously we collected the METEOSAT-2 infrared data. To calculate the accurate surface temperatures, the thermal IR band data must be properly calibrated. This can be done either empirically or theoretically. We calibrated these satellite data empirically. The IR image data were com- pared with the simultaneously measured surface water temperatures (in the case of METEOSAT Lake Balaton) and canopy surface temperature (for the LANDSAT Thematic Mapper) and relating them using linear regression tech- niques. The models used throughout results we have gained prove the world were reviewed to see if they can be applied under Hungarian conditions. The the possibility of their adaptation in Hungary. Further investigation for the application L5 TM 189/27/2 scene r. --~ 7/N'~'--, , ' : ~ . ~ / ,regy ", \B~bdlna.ANagyigmgnd~ f /£/ ) [ (J rWY--_SJ.,~ ~-~ 4 ( ~ .; .~ / f -'-g ffar{dnv~s~r-~, ~ / L--'4 " ,. .... -,-,_.__.~..,- b~'g. 1. Outline of TM scene used in the field experiment. A." place of the ground measurements, e: station mentioned in Table 1. (7)255