# Automatically Extracted Antarctic Coastline Using Remotely-Sensed Data: An Update
## 4 Results and Analysis  
### Validation of Extracted Coastline  
In order to assess the accuracy of the extracted coastline, we compared data from 2005 with 2004 MOA data. Figure 3 shows the comparison under the situation that the coastline is divided into five sectors: Weddell Sea (WS), Indian Ocean (IO), West Pacific (WP), Ross Sea (RS), and Bellingshausen Amundsen Seas (BAS). In general, the deviation between the two data sets is small (within a few kilometers). Insets in Figure 3 mark six areas of maximum deviation.  
In this and the following section, we conducted a statistical analysis to characterize the deviation between our extracted coastlines and the validation coastline (in terms of the difference along the perpendicular line between the two data sets). Table 2 includes the number of occurrences, as well as statistical analysis of the deviation (measured in kilometers in the shown intervals), between the coastline from the present study in 2005 and the MOA-2004 data set for the given five sectors. In general, the deviation between the two data sets is small (within a few kilometers). The total number of pixel points in each sector varies between \(1.7\times 10^{5}\) and \(3.9\times 10^{5}\). Data were obtained from a sample of 10,000 points in each sector. Table 2 shows that the largest deviation is less than 5 km (indeed, there are many points with identical coastline between the two data sets). The average deviation is found to be maximum in the IO sector (1.81 km) and minimum in the RS sector (0.76 km). In the BAS sector, the deviation is also high (1.64 km), yet with maximum variability (St. Dev. 6.36 km). The maximum deviation of 66.37 km is also encountered in the sector. The deviation between the coastline from the present study and the MOA coastline (green line and yellow line in Figure 4) is relatively high, due to coarse resolution (125 m) in the latter and the interannual difference between two data sets, as well as the differences in the methods used to delineate coastlines.  
Figure 4: Coastline in 2010, derived from present automated method (yellow) compared to the manually extracted coastline (red) from same image, and MOA coastline (green) in 2009 for the nine areas. The nine areas shown here are marked by footprints of Landsat images labeled as areas (**a-i**) in Figure 3.  
Figure 3: Coastline from the present method (blue) compared to the 2004 Mosaic of Antarctica (MOA) coastline (red) for the entire Antarctic. The green color indicates the geolocations of ice shelves around the Antarctica. Samples from each sector that highlight areas of remarkable difference between the two data sets are shown in the insets. Also, marked by footprints of Landsat images are locations of nine areas (**a-i**) where statistical analysis of the difference between the automated and manually extracted coastline was performed. The zoomed in Landsat images of the nine areas are illustrated in Figure 4.  
The length of the Antarctic coastline calculated from MOA data in 2009 and the present data in 2010 for the five sectors are shown in Table 3. For the MOA in 2009, the total length of the Antarctic coastline is 39,608 km and the length of the coastline for each sector is 4750.71 km (WS), 13,868.27 km (BAS), 6776.71 km (RS), 6833.04 km (WP), and 7379.27 km (IO). Compared to the length for each sector from the present results in 2010, the length in 2009 is always greater except for the coastline in the WS. The mean difference of length in these five sectors is 865.32 km. The difference (2010-2009) in each sector is 165.46 km (WS), \(-\)1645.29 km (BAS), \(-\)971.72 km (RS), \(-\)989.75 km (WP), and \(-\)885.30 km (IO). The coastline in MOA was extracted manually and the contour is less smooth than the output from the present results.