EVALUATION OF HARGREAVES BASED ON REMOTE SENSING METHOD TO ESTIMATE POTENTIAL CROP EVAPOTRANSPIRATION

Abstract

In arid and semi-arid regions, agricultural water consumption information is very important to managing and developing water resources. Potential crop evapotranspiration (ETc) is the major parameter in agricultural water resources management. Remote sensing techniques were involved in this work to evaluate Hargreaves method for estimating ETc depending on satellite data. The difference between air temperature (Tair) and Land Surface Temperature (LST) varies particularly by surface water status. Normalized Difference Vegetation Index (NDVI) was extracted from NOAA/AVHRR and landsat8 satellite data to calculate emissivity as an intermediate step for producing LST. Linear relation between Tair and LST was established and R 2 was 0.93. Reference evapotranspiration (ETo) was estimated using agro-meteorological data through FAO-Penman-Monteith (FPM) which used as standard method and Hargreaves (Har) method. To calibrate ETo-Har, the ETo-FPM was used under the same conditions. Landsat8 data acquired on 13 th of Aug. and 08 th of Aug. 2014 and were used to calculate Crop coefficient (Kc) based on satellite data (Kc-Sat). LST was used to predict Tair ( o C) in Aug. 2014. ETo estimated using Har method and was used with Kc-Sat to estimate ETc-Har. ETo-FPM combined with Kc-Sat to estimate ETc-FPM. ETc-FPM used to evaluate ETc-Har. The relation between ETc- FPM and ETc-Har was very strong where R 2 as high as 0.99.