A. Tsouni, D. Koutsoyiannis, C. Contoes, N. Mamassis, and P. Elias, Estimation of actual evapotranspiration by remote sensing: Application in Thessalia plain, Greece, Proceedings of the International Conference "Geographical Information Systems and Remote Sensing: Environmental Applications", Volos, doi:10.13140/RG.2.1.3025.1763, 2003.
As evapotranspiration is one of the main components of hydrologic cycle, its estimation is very important. Remote sensing technologies can assist to improve the estimation accuracy also providing means for computing evapotranspiration geographical distribution. In the present study, the daily actual evapotranspiration was calculated for 21 days uniformly distributed during the 2001 summer season over Thessaly plain. Three different methods were accordingly adapted and applied: the remote-sensing methods by Granger (Granger, 2000) and Carlson-Buffum (Carlson & Buffum, 1989) using satellite data together with ground meteorological measurements and an adapted FAO Penman-Monteith method, used as reference method. Satellite data, following the necessary processing, were used in conjunction with surface data from the three closest meteorological stations. All three methods, following their appropriate adaptation, exploit visible channels 1 and 2 of NOAA-AVHRR satellite images to calculate albedo and NDVI and infrared channels 4 and 5 to calculate surface temperature. FAO Penman-Monteith and Granger methods require mean surface temperatures, so NOAA-15 satellite images were used. For Carlson-Buffum method a combination of NOAA-14 and NOAA-15 satellite images was used, since the average rate of surface temperature rise during the morning is required. The results of the application are encouraging. Both Carlson-Buffum and Granger methods follow in general the variations of the FAO Penman-Monteith method. However, they underestimate evapotranspiration during the days with relatively high wind speed.
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