## 2 Materials and Methods
### Data Collection
#### 2.3.3 Data Processing  
The next step in _establishing effective data procurement methods for both before and after planned disturbances_ was to produce quality output products--specifically, georeferenced orthomosaics. Georeferencing is the process of pairing each image with its associated coordinates. This can be achieved in many different ways, such as with GCPs, RTK, PPK, or a combination of these methodologies [22; 61; 62; 63]. Georeferenced orthomosaics were produced for each image dataset, while those surrounding the PWA and Volz disturbances were used in the final land cover classification assessments. When testing processing methods for the prairie and forested sites, the procedures were mostly the same; however, some forested datasets performed better after adjusting two specific parameters in Pix4D. PPK was used in this study to both capture images and georeference the imagery but was corrected after the flight to ensure the most accurate image positions possible. To do this, EZSurv software was used for its compatibility with the selected PPK device and user-friendly interface. An appropriate datum and projected coordinate system were set to establish an appropriate spatial reference when performing corrections (Table 9). Then, RINEX (raw positioning) data from the flight was corrected using the nearest CORS location for each site. This was done for each dataset surrounding the selected prairie burn (PWA) and timber harvest (Volz) sites (Table 10). Once the image coordinates were corrected, this information was brought into Pix4D along with the associated image dataset to produce georeferenced orthomosaics [57; 65]. When in the Pix4D processing phase, several parameter adjustments were made--the processing speed, output quality, and reconstruction detail. The keypoint image scale (KPIs) in the \"initial processing\" step defines the scale at which the processing algorithm looks for similar pixels of identifying objects between multiple images in order to properly position each image within the orthomosaic [66]. For prescribed burn prairie sites, the default KPIs of \"1\" was used almost exclusively, while some selective harvest sites performed better with a reduced KPIs of \"%\" or \"%\", especially when some of the images contained motion \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**CORS** & **Distance** & **Mean** & **Mean** & **Constellations** & **Mean Position** & **Mean Position** & **Mean Position** \\
**Site** & **from Site** & **Fixed Epochs** & **Float Epochs** & **Used** & **Uncertainty (\%)** & **Uncertainty (\%)** & **Uncertainty (\%)** \\ \hline P775 & \
\begin{tabular}{c} 6 km \\ (3.7 mi) \\ \end{tabular} & 30,086 (99.9\%) &
\begin{tabular}{c} 3.2 \\ (0.012\%) \\ \end{tabular} & GPS & 2.15 cm & 2.18 cm & 2.43 cm \\ KYBO & 35 km (21.4 mi) & 23,302 (89.9\%) & 4869 (10.1\%) & GPS + & 2.7 cm & 2.65 cm & 2.73 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 10: NOAA CORS locations used for correcting PWA prairie burn (P775) and Volz timber harvest (KYBO) sites. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Datum** &
\begin{tabular}{c} **Projected** \\ **Coordinate System** \\ \end{tabular} & **Zone** & **Orthometric Surface** & **Estimated Error** \\ \hline World Geodetic System—1984 revision & Universal Transverse & & & \\ (WGS 84) & Mercator (UTM) & 16 North & Ellipsoidal & 2 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Datum and projected coordinate system used for georeferencing. NOTE: Estimated error obtained from World Geodetic System—‘WGS 84’’ [64]. blur. In some instances, adjusting the KPIS still was not enough to produce a quality georeferenced orthomosaic, and the calibration method was switched from \"standard\" to \"alternative\" [50]. Because the burn sites performed well with the default \"standard\" calibration method, the \"alternative\" was not tested for PWA.