EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

C-band Sentinel-1 data for estimating the basal crop coefficient and evapotranspiration of winter wheat  

Nadia Ouaadi1,2, Lionel Jarlan1, Saïd Khabba3,4, Michel Le Page1, Adnane Chakir3,5, Salah Er-Raki6, and Pierre-Louis Frison5
Nadia Ouaadi et al.
  • 1CESBIO, University of Toulouse, IRD/CNRS/UPS/CNES, Toulouse, France (
  • 2GMME/SURFACE, Meteo-France/CNRM, Toulouse, France
  • 3LMFE, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
  • 4CRSA, Mohammed VI Polytechnic University, Ben Guerir, Morocco
  • 5LaSTIG, Gustave Eiffel University, Paris, France
  • 6ProcEDE, Faculty of Sciences and Technologies, Cadi Ayyad University, Marrakech, Morocco

Estimating crop evapotranspiration (ETc) is of primary importance for irrigation management. The model commonly used for this purpose is the FAO-56 approach which consists of accurately estimating the basal crop coefficient Kcb. Historically, Kcb is derived from optical indices such as NDVI giving its sensitivity to vegetation cover fraction and to the Leaf Area Index. Nevertheless, optical data are disturbed by the presence of clouds. In this context, the objective of this work is to investigate the potential use of all-weather radar data as a substitute of NDVI to derive Kcb. The study is conducted over two winter wheat fields (Field 1 and Field 2) in Morocco, monitored during two agricultural seasons 2016-2017 and 2017-2018. Each field is equipped with an eddy covariance station allowing the estimation of ETc every 30 minutes. In addition, a weather station was installed over an alfalfa plot near the study fields. First, the backscattering coefficient and the interferometric coherence ( ρ at VV polarization) are derived from Sentinel-1 data with a 6-day revisit time and a spatial resolution of 10 m. Second, empirical relationships have between established between Kcb, on one hand, and the interferometric coherence and the polarization ratio, on the other hand and the results are also compared to the classical Kcb-NDVI (derived from Sentinel-2) method. The results show that good statistical metrics are obtained between Kcb and NDVI (R=0.77 and RMSE=0.14 for Field 1). Similar results are obtained also using ρ (R=0.76, RMSE=0.18). Finally, the Kcb is estimated from the calibrated relationships on one season and then used to estimate ETc. The results demonstrate reasonable estimates of ETc on Field 1 (R=0.70, RMSE=0.75 mm/day and bias=-0.18 mm/days) using Kcb-ρ. By contrast, a significant overestimations is highlighted both with  (bias=0.73 mm/day) and NDVI (bias=1.46 mm/day) over Field 2. Interestingly, the Kcb-ρ relationship is more consistent in the estimation of ETc when changing from one field to another. These outcomes open new perspectives for the estimation of ETc from radar data as a potential substitute of NDVI in case of persistent cloud cover.

How to cite: Ouaadi, N., Jarlan, L., Khabba, S., Le Page, M., Chakir, A., Er-Raki, S., and Frison, P.-L.: C-band Sentinel-1 data for estimating the basal crop coefficient and evapotranspiration of winter wheat  , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14819,, 2023.