## 2 Data Collection and Preprocessing
### Landsat Imagery  
The main source of imagery used in this study is satellite imagery of the glaciers of interest gathered exclusively via the Landsat program publicly available through the National Aeronautics and Space Administration's (NASA) [11]. The Landsat data is stored in online databases and is freely accessible and downloadable via the web. The Landsat images along with the metadata (and much more) are available via the United States Geological Survey's Earth Explorer webpage found at [[https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/)]([https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/)) (accessed on 16 February 2021). It must be pointed out that, Sentinel program sponsored by European Space Agency provides satellite imagery with better resolution (in some spectral bands) taken by Sentinel-2 satellite. However, the Sentinel program began in 2015 and an inventory of only about 8 years of satellite imagery is available through this program. In contrast, the Landsat program started in 1972, provides more than 5 decades of data available. Moreover, satellite imagery with better resolutions is only available commercially for a much shorter period than a decade.  
The images of each glacier are captured at specific dates based on the glacier's geographic coordinates. Landsat has a 16-day return time, and the data is collected over  
Figure 3: Glaciers of Interest. Left: Gorner. Right: Franz Josef.  
several decades. The data has been publicly available since 2008 which has made it an attractive database of satellite imagery for scientists performing multidecade studies. In the preprocessing step of this study, we removed those scenes where the glaciers were obscured by clouds or mountain shades, and scenes with degraded imaging due to sensor malfunctioning. An example of image degradation can be found in the Landsat 7 (one of the multiple Landsat platforms with available data) image products. After launch, the Scan Line Corrector (SLC) went off line and due to this malfunction images will contain a zig-zag pattern. This becomes an issue when the pattern intersects with the object of interest as it is depicted in Figure 4.  
The Landsat images are collected with a multispectral sensor. This capability implies that each of the images contains several spectral bands. Each of these spectral bands has its own wavelength range of the electromagnetic spectrum. Multispectral imaging capability enables different views of the same scene highlighting features of interest that could be better viewed in created image in a specific band.  
Figure 5 shows the specific breakdown of a typical multispectral Landsat 7 image into its spectral bands as well as band specific images in false color along with terminus localization process. In this analysis the dataset was created from a collection of Landsat 7 and 8 images for both glaciers under consideration. The initial data pull consisted of 511 images in total for both glaciers, 263 for Franz Josef and 248 for Gorner. All of the original images fall in the date range January 2000 through November 2021. After cleaning the data for images where the glacier was obscured by clouds or shadows the final data sets for each glacier were as follows: Franz Josef data range is August 2000 through August 2021 and in this time frame 93 useful images were retained, while for Gorner the date range is May 2000 through October 2021 with 97 useful images retained.  
Figure 4: Example of Landsat images removed from dataset shown in false colors. Cloudy and invisible (**Left**); Covered by mountain shadow (**Middle**); Sensor malfunction (**Right**).  
Figure 5: (**Left**) Multispectral band information for images taken by Landsat 7. (**Middle**) Top Franz Josef; Bottom: Gorner; from left to right: Band 1, Band 5, Band 6 shown in false colors. (**Right**); Terminal Identification process.