**5. Conclusions**

UAVs offer an opportunity to make flexible, efficient radiation measurements at many locations and scales. Here, we validated a method of measuring albedo by UAV while minimizing payload and technical requirements. We found that UAVs provided stable albedo measurements across multiple flights over a mixed hardwood forest, with results that were well within the range of tower-estimated albedo at similar forested sites. Simultaneous albedo estimates by UAV and a fixed tower at the same site showed that the two methods produced near identical results. Finally, we demonstrated that in-situ albedo measurements (tower and UAV) capture more site-to-site variation in albedo than satellite measurements. Overall, we show that UAVs produce reliable, consistent albedo measurements that can capture crucial surface heterogeneity, clearly distinguishing between different land uses.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2072-4292/10/8/1303/ s1, Table S1: Dates, times, and locations of described UAV flights, Table S2: Latitude and longitude of UAV satellite pixels Table S3: Latitude and longitude of tower satellite pixels, Table S4: Blue sky albedo estimates for sites in Tully, NY. Table S5: Current FAA requirements for UAV research within the United States.

**Author Contributions:** Conceptualization, C.R.L.; UAV and Satellite Dataset, C.R.L.; Harvard and Bartlett Forest Dataset, A.D.R.; Durham Forest Dataset, E.B.; Validation and Analysis, C.R.L.; Writing-Original Draft Preparation, C.R.L.; Writing-Review & Editing, C.R.L., E.B., and A.D.R.

**Funding:** This research was funded by the David R Atkinson Center for a Sustainable Future, through the Academic Venture Fund program. Harvard and Bartlett Forest measurements were funded by the National Science Foundation through the LTER program, which has supported research at Harvard Forest (DEB-1237491) and Bartlett Experimental Forest (DEB-1114804).

**Acknowledgments:** Timothy Fahey was the primary investigator on this grant, and is particularly thanked for his support. The authors would also like to extend sincere thanks and appreciation to Martin LaChance of UAV Imaging Systems for his expertise and hard work in realizing this project.

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