# Landsat Surface Product Validation Instrumentation:
## 2 Data Collected
### Reflective  
For surface reflectance measurements, efforts were focused on three specific times of day as follows: 10:30 AM, 12:30 PM, and 2:30 PM local time. These three times were chosen to represent typical morning and afternoon satellite data overpass times, and a time in between close to solar noon when change in solar illumination during data collection would be minimal was also chosen. All teams using ASDs, as well as UAS flights, would  
Figure 8: Weather conditions on 31 August 2021. All-sky photos are shown for approximately 10:30 AM (15:30 UTC), 12:30 PM (17:30 UTC), and 2:30 PM (19:30 UTC), respectively. A timeline of the wind speed recorded by the the Brookings, SD airport ASOS station is shown in the lower figure.  
begin at these times so that measurements were made within a few minutes of each other. Thus, all measurements were made with substantially the same illumination conditions. All ASD measurements were made following the protocols described in [15,17] from a nadir-viewing geometry; that is, the center line of their field of view was directed normal to the Earth's surface and the UAS followed the ASD measurement sequence. Table 1 provides details for all flights conducted during BigMAC.  
Surface reflectance data were all recorded with hyperspectral sensors at essentially 1 nm resolution. However, since the primary emphasis of the BigMAC campaign was to determine the best procedures for measuring surface reflectance for the evaluation of Landsat products, all hyperspectral data were banded into Landsat 8 OLI reflective bands. These banded surface reflectance values were calculated on both days, all three acquisition times, for all reflectance targets, and for each OLI band (except the Cirrus band which normally is unable to view land surfaces). The mean values and standard deviations of the data were recorded and compared for each measurement methodology. Overall means and standard deviations across all days and all teams were also recorded. Key measurements of interest were consistency in measurements performed in the mornings, at noon, and in the afternoon to determine what might be expected for the operational precision of the surface reflectance measurements. In addition, certain targets--the Pernaflect panels and the 'Mystery' panels--were absolutely calibrated by independent laboratories, and the measurements of these panels were evaluated for absolute accuracy.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**30 August 2021** & & & \\ \hline
**Launch (UTC)** & **UAS Payload** & **Mode** & **Altitude (AGL)** \\ \hline
1539 & MX-1 & flightlines & 60 m \\ \hline
1545 & SWIR & flightlines & 60 m \\ \hline
1615 & MX-2 & flightlines & 60 m \\ \hline
1645 & MX-2 & stare & 60 m \\ \hline
1716 & MX-1 & flightlines & 60 m \\ \hline
1718 & SWIR & flightlines & 60 m \\ \hline
1735 & MX-2 & flightlines & 60 m \\ \hline
1832 & MX-2 & stare & 60 m \\ \hline
1913 & MX-1 & flightlines & 60 m \\ \hline
1914 & SWIR & flightlines & 60 m \\ \hline
1916 & MX-2 & flightlines & 60 m \\ \hline
2058 & Mavic RGB & flightlines & 60 m \\ \hline
**30 August 2021** & **Windy** & & \\ \hline
**Launch (UTC)** & **UAS Payload** & **Mode** & **Altitude (AGL)** \\ \hline
1512 & MX-1 & flightlines & 60 m \\ \hline
1513 & SWIR & flightlines & 60 m \\ \hline
1517 & MX-2 & flightlines & 60 m \\ \hline
1704 & MX-1 & flightlines & 60 m \\ \hline
1706 & SWIR & flightlines & 60 m \\ \hline \hline \end{tabular}
\end{table}
Table 1: Details of UAS flights conducted during BigMAC.