# Automatically Extracted Antarctic Coastline Using Remotely-Sensed Data: An Update
## 4 Results and Analysis
### Comparison Against Manual Extraction  
The extracted coastlines in the nine areas from 2010 data, marked by the footprints of Landsat images in Figure 3, were compared to the manually extracted coastline based on visual interpretation of Landsat images. Results are presented in Figure 4 with the MOA-2009 coastline included. Visual comparison confirms a small deviation between the manual and automated extraction methods. However, in Figure 4c, there is a large discrepancy because the data for MOA coastline [24; 25] are from a different year when compared to our data. This suggests a remarkable temporal change of the coastline in that area.  
In addition, we chose 1000 points, at 60 m interval, in each area and computed their deviation from the manually extracted coastline. The visual comparison is shown in Figure 4 and the distribution of the deviation is included in Table 4. The range of deviation is divided into five bins, as shown in Table 4 (note that, unlike Table 2, units are in meters). The number of occurrences within each bin is also shown. Of the differences, 92.32% are within 100 m, with mean values between 19.47 m (Figure 4i) and 71.39 m (Figure 4g). The overall mean deviation is 38.15 m and the greatest deviation is 586.27 m, noticed in Figure 4c and the minimum deviation is 0 m.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{6}{c}{**Percentage of Occurrences of Each Deviation**} \\ \hline Deviation (km) & WS & BAS & RS & WP & IO & Total \\ (0–5) & 97.32\% & 95.83\% & 97.78\% & 96.92\% & 94.01\% & 96.37\% \\ (5–10) & 2.44\% & 1.35\% & 1.47\% & 2.22\% & 2.93\% & 2.08\% \\ (10–20) & 0.24\% & 0.89\% & 0.75\% & 0.86\% & 1.16\% & 0.78\% \\ (20–30) & 0\% & 0.53\% & 0\% & 0\% & 0.59\% & 0.23\% \\ (30–60) & 0\% & 1.4\% & 0\% & 0\% & 1.31\% & 0.54\% \\ Mean (km) & 0.89 & 1.64 & 0.76 & 0.93 & 1.81 & 1.21 \\ St. Dev. (km) & 1.45 & 6.36 & 1.54 & 1.72 & 5.94 & 4.10 \\ Maximum (km) & 12.83 & 66.37 & 17.53 & 16.59 & 59.25 & 66.37 \\ Minimum (km) & 0 & 0 & 0 & 0 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Percentage of deviation between the coastline products from the present method in 2005 and the MOA 2004 data set for the five sectors (in km).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{6}{c}{**Length of Coastlines (km)**} \\ \hline
**WS** & **BAS** & **RS** & **WP** & **IO** & **Total** \\ \hline
2009 (MOA) & 4750.71 & 13,868.27 & 6776.71 & 6833.04 & 7379.27 & 39,608 \\
2010 (this study) & 4916.17 & 12,222.98 & 5804.99 & 5843.29 & 6493.97 & 35,281 \\ Diff. 2010–2009 & 165.46 & \(-\)1645.29 & \(-\)971.72 & \(-\)989.75 & \(-\)885.3 & \(-\)4327 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Coastline length in each sector (km) in 2009 (MOA) and 2010 (this study). WS, Weddell Sea; BAS, Bellingshausen Amundsen Seas; RS, Ross Sea; WP, West Pacific; and IO, Indian Ocean.  
Based on examination of the data from this test, we found that errors over 100 m were mainly the results of the misinterpretation of offshore sea ice as being a part of an ice sheet (i.e., part of the continent), such as the part in the brown circle in Figure 4g. Additionally, these errors could have been caused by the manual extraction of coastline from a Landsat image when fast ice was misidentified as part of the ice sheet, such as the part in the red circle in Figure 4c.