**5. Conclusions**

In this study, we evaluated whether EOS and sUAS ET estimates fundamentally differ over same period of time. We showed that more traditional heat balance approaches to EOS RSE can be compromised by field conditions, such as soil saturation and excessive air temperature, and lead to overestimation of ET compared to other methods. Further, we showed that over the course of the growing season, sUAS values largely follow seasonal patterns and track EOS RSE values, but that ET variance is reduced by isolating canopy pixels. While EOS and sUAS ET estimates do not fundamentally differ over the same study domain and same period of time, comparing upscaled sUAS ET to EOS ET estimates within and across pixels, we showed that unmasked high resolution sUAS ET estimates have the highest variance but that EOS EEFlux ET values have high variance too. These "mixed pixels" inherent in EOS data obscure important signals in ET estimation through inclusion of soil fraction, and given that vineyards change over the course of a growing season in terms of biomass and leaf area index can change, caution should be used when evaluating ET whether using traditional energy balance models or RSE proxies. These findings can provide growers with guidance on their own use of new RSE products and sUAS platforms for calibration and verification.

**Author Contributions:** Conceptualization, J.H.V.; Methodology, J.H.V., M.K., A.M.R., J.M.-A.; Software, M.K., A.M.R., L.B.; Formal Analysis, J.H.V., M.K., A.M.R.; Resources, J.H.V., J.M.-A., S.C.; Investigation, J.H.V., M.K., A.M.R., L.B.; Writing—original draft preparation, J.H.V., M.K.; Writing—review and editing, J.H.V., M.K., A.M.R., J.M.-A., S.C.; Visualization, J.H.V., M.K., A.M.R.; Supervision, J.H.V., A.M.R.; Project Administration, J.H.V., A.M.R., S.C.; Funding Acquisition, J.H.V., J.M.-A., S.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was partially supported by the National Robotics Initiative (NRI) grant no. 2017-67021-25925 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. Lorenzo Booth was partially supported by the NSF under grant DGE-1633722. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of NSF. Additional support was from the Public Policy Institute of California (PPIC) Steyer-Taylor Fellowship and the UC Merced Center for Information Technology Research in the Interest of Society (CITRIS) and CITRIS Aviation.

**Acknowledgments:** We gratefully acknowledge the lab and field assistance of Andreas Anderson, and support from Brandon Stark of the University of California Drone Safety Center. We thank E. & J. Gallo Winery for access to the site, and their science team of Nick Dokoozlian, Maria Mar Alsina, Brent Sams and Luis A. Sanchez for insights to the study system.

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