**4. Summary**

In this study, a methodology developed by the University of Thessaly, Greece, is used for the calculation of actual evapotranspiration values using Sentinel imagery. This methodology suggests a modification and improvement of the initial ESA's SEN-ET methodology. The SEN\_ET methodology is supported by SNAP software utilizing Sentinel-2 and Sentinel-3 satellite imagery, as well as meteorological data from the Weather Forecast and Research (WRF) model, to estimate daily ETa values. The results of the experiment showed that there is a clear overestimation of ETa in some periods, especially during July and August. At the next step of the method's improvement, it is important to use in-situ measurements.

**Author Contributions:** Conceptualization, N.A., G.A.T. and I.F.; methodology, I.F.; software, N.A. and G.A.T.; validation, M.S., S.S. and P.S.; formal analysis, P.S.; investigation, G.K.; resources, G.K.; data curation, G.K.; writing—original draft preparation, M.S. and N.A.; writing—review and editing, M.S.; visualization, N.R.D. and N.D.; supervision, N.R.D. and N.D.; project administration, S.S. and N.R.D.; funding acquisition, N.R.D. and N.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the project HubIS under the PRIMA 2019 program of the European Commission (HORIZON EUROPE).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors acknowledge the European Space Agency for the supporting data and materials.

**Conflicts of Interest:** The authors declare no conflict of interest.
