Investigation of spatial relationships between crop coefficients and specific ground based vegetation indices for Karla watershed, Greece

The objective of this work is the investigation of the specific relationships between actual evapotranspiration based crop coefficients and vegetation indices adapted to Karla Watershed, central Greece. Surface Energy Balance Algorithm for Land (SEBAL) was used to derive monthly actual evapotranspiration (ET) and ETrF values during the growing season of 2012. The methodology was developed using medium resolution Landsat 7 ETM+ images. Meteorological data from the archive of the Institute for Research and Technology, Thessaly (I.RE.TE.TH) have also been used. Fields with cotton, wheat, alfalfa, corn and sugar beets are utilized. During the same period, in-situ radiometric measurements were generated with the use of the field spectro-radiometer GER1500 giving specific spectral signatures for each crop. Filtering of reflectance values with the use of relative spectral responses (RSR) gives the opportunity to match the spectral measurements with Landsat ETM+ bands and compute VI like NDVI, SAVI, EVI and EVI2 using the same remote sensing formulas as the ETM+ conventional procedures. New relationships are derived and NDVI, SAVI, EVI and EVI2 are tested separately for each crop. Special attention is given to the constant L inside the SAVI relationship. The main advantage of the new approach is that is more crop specific and it less time consuming because there is no need for atmospheric correction.