# [PERSON] Glacier Status Analysis Based on Historical Data and Moving Detection Using RPAS
## 7 Discussion and Conclusions  
The first part of this research looked at the possibility of monitoring the flow rate and its distribution of the face of the Knud Rasmussen Glacier in eastern Greenland using RPAS based on point cloud time changes detected from two overflights. According to the  
Figure 23: The Knud Rasmussen Glacier area changes between 1932 and 2020; the basic state was the year 1984 (i.e., the state “zero”). Between 1932 and 1984, we do not have data about the glacier status. Figure 22: A final interpretation of the Knud Rasmussen Glacier changes between 1932 and 2020 (2019 * are data from the eBee drone, some parts were missing). available results, the most significant changes occur in the middle part of the studied glacier. For computing the displacement of both point clouds derived from photo-sets in different time, the M3C2 distance from CloudCompare software was used. The displacement values histogram shows that the changes rarely exceed three m. A typical movement of the middle part of this glacier can be from 2 to 3 m in 4 h, but a mean speed based on the local histogram maximum is only 1 m in a time span of 4 h. There is a possible error of up to RMS 67 cm, given the inaccuracy of joining both point clouds. In conclusion, the use of a drone for monitoring the speed of the movement and its distribution of the glacier is possible even after a relatively short time span. The fastest running ones have a speed in the middle of up to tens of m per day, such as the Eqi Glacier or the Jakobshavn Glacier in west Greenland. In the case of the Knud Rasmussen Glacier, the flow rate in the middle nearby the glacier face is considerable and can reach a value of around 12-15 m per day at most; however, this is only an extrapolation, but it correlates with the measurement on other glaciers. Here, problems were found: only a short time span was used, only one measurement in the summertime was carried out, the parameters of the flight were not ideal due to the local conditions and lack of time. Any precisely measured control points were used. The problems with the precision and time of flight can be nowadays solved with a modern eBee RTK with a base station and with better quality batteries, and with more time for these experiments. The second goal of our research was aimed at an analysis of using and joining different image data for the monitoring of this glacier, mainly new processing of old historical aerial oblique images from the 1930s. From the historical images, we can deduce that the Knud Rasmussen Glacier receded inland mainly after 2011. This glacier retreat inland is not so progressive as that of other glaciers, which have receded km inland due to climate change. An analysis of historical aerial images, Landsat and Sentinel satellite images, and new drone orthophoto shows that the front of the Knud Rasmussen Glacier was in practically the same place until 2011. Only later did the glacier begin to recede. Unfortunately, data from 1933 to 1983 is unreachable or missing for us. We could not find out what the situation was in the fifty missing years. The new drone images, such as Sentinel data from 2019 to 2020, show the accelerated retreat of the glacier front in recent years. However, the newest (2019-2020) and the oldest (1932-1933) image data were obtained in the summer, satellite data from Landsat were always acquired on the last day of the year, and the cloud-free data from the Sentinel satellite were taken partially in summertime and partially in the autumn. Thus, a seasonal change is possible in this summer data, and the data have less significance with regard to long-term development. Even so, it is certain that the melting of the glacier is happening, and it is accelerating. Conceptualization, K.P. ; methodology, K.P. and K.P.J. ; technical advisory and supervision, K.P. and J.S. ; data processing, K.P., K.P.J., and J.S. ; investigation, K.P. ; writing--original draft preparation, K.P. ; writing--review and editing, K.P.J. and J.S. ; visualization, [PERSON], K.P.J., and J.S.