Operative Approaches To Determine Crop Water Requirements From Earth Observation Data: Methodologies And Applications

The estimation of evapotranspiration ET represent the basic information for the evaluation of crop water requirements. A widely used method to compute ET is based on the so-called 'crop coefficient' Kc, defined as the ratio of total evapotranspiration by reference evapotranspiration ET0. As confirmed by recent standard procedures of F.A.O., under given climatic conditions, the value of crop coefficient is related to canopy variables representing the crop growth stage such as canopy height, fractional vegetation cover and Leaf Area Index. Considering that these canopy variables influence the spectral response of vegetated surfaces, a direct correspondence between Kc and reflectance measurements can be established. On this baseline, two approaches have been considered in Demeter for the operative estimation of crop water requirements: a first one, based on the correlation between the Near Difference Vegetation Index and the value of basal crop coefficient; a second one, where Kc is calculated by using reflectance-based estimates of canopy variables. A comparative analysis of the proposed methodologies is presented with reference to the investigations carried out for the implementation of DEMETER project in Italy and Spain on different types of crops.