# Rapid-DEM: Rapid Topographic Updates through Satellite Change Detection and UAS Data Fusion
## 3 Results
### Priority Queue  
The binary change mask (Figure 6A) masked 0.19\(km^{2}\) or 1.47% of the Walnut Creek watershed resulting in 162 change objects, while the priority change map (Figure 6B) indicated that 83% of the study area had no change and 7.41% had high priority change. The priority change objects had a mean priority change of 3.7 \(\pm\) 2.1 (Figure 6C) and a mean  
Figure 5: The (**A**) before mosaic (1 June 2018–14 July 2019) and (**B**) after mosaic (15 July 2019–26 August 2020) land cover classification results were used to develop the priority map of the Walnut Creek watershed.  
area of 0.056 km\({}^{2}\)\(\pm\) 0.076 km\({}^{2}\) (Figure 6D). The priority queue contained 109 locations (Figure 6E), 51 (47%) were validated as containing change while 58 (53%) were deemed as noise. However, filtering the priority queue to only include locations with priority values (0.016) and areas (0.04 km\({}^{2}\)) greater than the median improved the accuracy of the results (Figure 7). The filtered priority queue contained 42 locations with 9.5% error and a 25.5% loss of valid low priority area.  
Figure 6: By zooming in on the northwest corner of the Walnut Creek watershed the steps involved in calculating the priority queue are illustrated as follows: (**A**) binary change mask was used to filter noise seen in the (**B**) priority change map. The (**C**) mean priority change of each of these objects was then calculated and weighted by the (**D**) change objects area producing the (**E**) priority queue. The priority queue was then converted to (**F**) priority queue vector for use with UAS flight planning software.  
The priority context map revealed that the priority queue identified 26 forest clearings, six new buildings, seven demolished developments, and three newly developed areas (e.g., parking lot). Forest clearings were the most important type of change identified by the priority queue and represent 9 of the top 10 identified locations (Figure 8). New buildings represented the second most highly ranked topographic change detected by the priority queue with an average rank of 20 th \(\pm\)10 in the priority queue. While demolished developments and newly developed areas were the third and fourth ranked changes detected by the priority queue.  
The top priority area (Site 1) was identified as a forest clearing in the western head-water region of the Walnut Creek watershed. Site 1 is planned to be a large multi-purpose development with mixed residential and commercial accommodations, and the construction is scoped to be completed in the Spring of 2022 (Figure 9). The before (1 June 2018-14 July 2019) and after (15 July 2019-26 August 2020) mosaics visually show that the land cover changed from forested to mostly barren. The classification maps identified the change as a 96% decrease in forest land cover to barren, developed, and grass land cover types giving the object a mean priority change value of 5.2. Site 1 had a priority value of one and an area of 0.5 km\({}^{2}\).  
Figure 8: The top ten priority areas labeled with additional context to the type of change that occurred at each location.  
Figure 7: Median thresholds of the priority value and site area improved the overall accuracy of the priority queue.