# Landsat Surface Product Validation Instrumentation:
## 7 Summary/Conclusions/Path Forward  
### Summary  
With regard to precision, or repeatability, the results for the various technologies may be summarized as follows. The use of personnel carrying portable spectroradiometers has long been the standard for field measurements of surface reflectance. In the case of BigMAC, all teams used the ASD FieldSpec radiometer. For brighter targets, those in the range from 0.3 to 0.5 reflectance units, precision was in the range of 0.01-0.02 reflectance units. While, for darker targets, that is from 0.03 to 0.06 reflectance units, this approach was capable of measuring surface reflectance repeatably at 0.001-0.002 reflectance unit. For UAS-based measurements, the precision for brighter targets was comparable to the  
Figure 20: Photo of the deployed Arable radiometer on left. Plot of the Arable calibration accuracy on right. “Truth” refers to coincident spectroradiometer measurement. ground-based spectroradiometer results. However, for darker targets, the repeatability of UAS-based measurements increased to approximately 0.005. This difference may be due to, at least in part, the small physical size of the dark targets with respect to the UAS sensor's GSD. Results derived from the larger, more pristine Permanflect panels were an indicator of the influence of target type on the measurements. This highlights the trade-off that is always present when using natural targets in the field versus highly developed human-made targets. When considering the accuracy of surface reflectance measurements, the primary factor that must be understood is traceability. In the case of the BigMAC campaign, there were essentially two traceability paths. Differences in these paths led to at least a 0.02 reflectance unit difference among the sets of measurements defined by these two paths. For ground-based spectroradiometer measurements, accuracy in the range from 0.02 to 0.03 reflectance units was achievable for bright targets. Results for dark targets were somewhat mixed, but an accuracy of approximately 0.02 units was attainable. Because of the traceability path for the UAS-based radiometers, accuracy was lower than the ground-based radiometers. However, accuracy in the range from 0.02 to 0.04 reflectance units was attained. Surface temperature measurements with an accuracy of 1-2 \({}^{\circ}\)K were attained in BigMAC. UAS-based measurements using the FLIR instrument recorded temperatures of water targets consistent with in situ TidbiT sensors, with an agreement of 1 \({}^{\circ}\)K. With respect to non-water targets, measurements of the FLIR instruments agreed with contact thermocouple instruments to 2 \({}^{\circ}\)K. These measurements are consistent with the specifications of the instruments reported previously. Additionally, measurements between the UAS-based FLIR sensor agreed with the \(\mu\)FTIR ground-based measurements to 1 \({}^{\circ}\)K.  
Mirror-based measurements via the MELM are dependent on performing the background subtraction step accurately and on determining the equivalent diffuse reflectance of the mirrors. The MELM method results demonstrate consistency with the theoretical uncertainties of 7% when applied to UAS measurements. Results from other experiments indicate that this uncertainty can be greatly decreased with improvements in operation of the UAS sensor platforms. When using MELM for satellite observations in BigMAC, accuracies in the range of 0.02-0.03 reflectance units were attained, which is commensurate with differences observed for ground-based measurements between traceability paths. It should be noted that overcoming logistical constraints for satellite-based MELM during the BigMAC campaign could help yield improved results and this is the subject of ongoing work. Lastly, the Arable Mark 2 radiometer can be used in conjunction with ground truth information to validate surface reflectance products.