In semi-arid regions, irrigation represents over 85% of water use, making its efficient management crucial. Accurate estimation of evapotranspiration (ETR) is essential to determine crop water requirements. The FAO-56 method, based on crop coefficient (Kc), is widely used for ETR estimation. While NDVI from optical data has been applied to estimate Kc, it shows limited variation for tree crops despite phenological changes. Radar data, however, are sensitive to structural vegetation changes at the wavelength scale. This study evaluates the capability of C-band radar data to estimate Kc for olive trees. Empirical relationships were assessed between Kc and temporal coherence (ρ) in VV and VH polarizations, as well as backscattering coefficients (σ0) from Sentinel-1 over the 2021 seasonal cycle. A high agreement is observed between σ0VV and Kc, with a correlation coefficient of 0.76 and an RMSE of 0.11, highlighting the capability of radar data for improving evapotranspiration estimation in tree crops.
Elallaoui et al. (Fri,) studied this question.