# Landsat Surface Product Validation Instrumentation:
## 7 Summary/Conclusions/Path Forward
### Path Forward  
The BigMAC results clearly indicated that the handheld portable spectroradiometer continues to provide highly accurate, repeatable measurements whenever ground truth is needed. However, it is not practical to use this technology over a widely distributed geographical region for a significant period of time due to the high time demands and costs associated with the field staff needed to complete these surveys. Thus, it remains a viable method to maintain the calibration of automated instruments deployed for long periods of time. UAS deployed instrumentation is not feasible for similar reasons--high deployment costs. UAS deployments require a certified pilot, permits, and substantial investments in equipment and time to complete. UAS technology continues to improve and can potentially provide the prolonged cover of large areas. Therefore, reassessing deployments of UAS instrumentation in the future could help identify new ways to apply these methods. TidbiTs can be used to collect simple, robust, and accurate water temperature data. However, additional study would be needed to optimize deployment for long term autonomous operation, as well as understand how the TidbiT measurement relates to the actual surface temperature of the water. MELM can provide validation over many square kilometers of imagery but requires a portable mirror system that can work well with Landsat GSDs for operational deployment scenarios. Uncertainties have been demonstrated that meet the needs for surface reflectance validation but can be affected by background subtraction and the mirror design/size. Additional future studies could help optimize background subtraction and mirror design and size when using MELM. This is technology that needs to be monitored for future use. Arable Mark 2 radiometers could be incorporated immediately to validate surface reflectance products. They could be widely deployed and would operate independently with little ground truth required over the course of a growing season, but they would have to be removed and stored in cold temperatures (sub 0 \({}^{\circ}\)C). Some effort will be required to ensure spectral differences can be addressed so they are compatible with Landsat spectral bands, and Arable Mark 2 radiometers are only limited to the VNIR wavelengths at this time. BigMAC was not an exhaustive test of all available surface reflectance and temperature measurement technologies. Other methods are available and/or are being developed at the time of writing. The continued improvement of these technologies could result in more accurate surface reflectance and temperature products for the Earth remote sensing community. Conceptualization, D.H.; methodology, D.H., J.M., M.S., L.L., A.G., R.E., D.C., T.B., C.D. and B.R. ; software, M.S., R.E.,T.B. and B.R. ; formal analysis, D.H., M.S., R.E, A.G. and B.R. ; resources, J.M., L.L., E.M., L.F., N.R., T.B., C.D. and B.R. ; data curation, L.L., J.M., J.L., L.F., D.C., N.R., T.B., C.D. and B.R. ; writing--original draft preparation, D.H.; writing--review and editing, M.S. and R.E. ; visualization, D.H., M.S., R.E. and B.R. ; supervision, D.H., E.M., A.G., N.R. and C.D. ; project administration, D.H., J.M., E.M., A.G., N.R. and C.D. All authors have read and agreed to the published version of the manuscript. This work was performed by a KBR contractor supporting the ECCOE under USGS contract number 140G0121D0001. Not applicable. The data presented in this study, collected by USGS, are openly available in ScienceBase at [[https://doi.org/10.5066/P9E3F6](https://doi.org/10.5066/P9E3F6) LV]([https://doi.org/10.5066/P9E3F6](https://doi.org/10.5066/P9E3F6) LV), accessed on 10 December 2024. The authors would like to express their gratitude to [PERSON] and [PERSON] for their support during the field campaign. They also extend their appreciation to [PERSON] for their valuable insights into SPARC technology. The authors thank the anonymous reviewers for their constructive feedback, which helped improve the clarity and quality of this manuscript.