Utilization of SEBAL Algorithm and Landsat8 Data for Estimation of Evapotranspiration – A Case Study: Tatra Mountains Region

The evapotranspiration is one of the climate elements, which plays an important role in water balance, and affects the ecosystem of any region. Accordingly, there are many mathematical equations and algorithms that found and designed to calculate and estimate the values of evapotranspiration, either based on data from weather stations or other sources in areas devoid from weather stations. Remote sensing data are one of the important sources and techniques to estimate the values of evapotranspiration. Landsat8, which was launched in early 2013, as a new source of remote sensing data, still some reluctance from researchers to use Landsat8 data, due to uncompleted reflectance and albedo calculation parameters of the sensor. In fact, this research represents a serious and aggressive attempt to use Landsat8 data in estimation of evapotranspiration. The surface reflectance values are calculated according to COST method for atmospheric correction and the effect of terrains are corrected based on ESTER DEM data, while a new equation is implemented to calculate the surface albedo, both parameters represent the first step to achieve the inputs spatial modelling of solar radiation and ET calculations. The study area is located in Tatra Mountains, which are natural border between Poland and Slovakia. The Tatra Mountains are one of the most valuable areas in Poland and Slovakia. Furthermore, these areas are protected (Polish and Slovakian National Parks).geologically the area was subjected to tectonic uplift caused mixing igneous rocks, metamorphic rocks and sedimentary rocks. The High Tatras are constructed of igneous rocks, mainly granites, Western Tatras are mostly built of metamorphic rocks (gneisses and schists), igneous (granites) and in certain parts of the sedimentary rocks. The Bielskie Tatra Mts. and the Siwy Wierch massif are built of limestone. Selected area is characterised by the lack of weather stations. The main objectives of this study are to utilize the remote sensing represented by Landsat- 8 data to calculate the values of evapotranspiration based on SEBAL algorithm. The data of Landsat8 OLI/TIRS with Path 188/Row 26, acquired on 08-SEP-2013, and the one arc-second resolution ASTER digital elevation model with some reference weather parameters are used as inputs for the models. The analyses are curried out using 16 ERDAS models, designed to calculate the various parameters related to solar radiation i.e surface radiance surface reflectance, surface albedo, NDVI, LAI, surface emissivity, surface temperature, net radiation, soil heat flux, sensible heat flux, latent heat flux, which are used later to calculate the hourly and daily evapotranspiration in study area. The results of pixel wise calculations shows, the values of surface temperature are varied from 6.2 oc at area covered by snow to 34.6 oc at bare rocks area, while the spatial variability of evapotranspiration (ET) for different land covers shows, the hourly ET ranged from 0 to o.72 mm/hr., the daily ET varied between 0.0 to 17.0 mm/day. Generally, the results proved the efficiency of Landsat8 data in calculation of all the required solar radiation parameters for estimating the ET values in a pixel wise when compared to results from other satellite data.