Can radar signals enhance thermal and optical bands for monitoring water status of olive trees?

¹ LMFE, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
² LaSTIG, Gustave Eiffel University, Paris, France
³ CRSA, Mohammed VI Polytechnic University, Ben Guerir, Morocco
⁴ AgroBiotec Center, Faculty of Sciences and Techniques, Cadi Ayyad University, Marrakech, Morocco
⁵ National School of Applied Sciences, Cadi Ayyad University (UCA), Safi, Morocco
⁶ CESBIO, Centre d’Etudes Spatiales de la Biosphère, Toulouse, France

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 22 May 2026

Abstract

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 K_c, 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.