# Automatically Extracted Antarctic Coastline Using Remotely-Sensed Data: An Update
## 3 Method
### Data Pre-Processing  
Here, Landsat-7/8 images were processed to L1 GT (Systematic Terrain Correction) products, which provide the highest level of radiometric calibration and terrain correction (details can be found in the website of the United States Geological Survey-USGS, [[https://www.usgs.gov/](https://www.usgs.gov/)]([https://www.usgs.gov/](https://www.usgs.gov/))). For Landsat-7 ETM+ and Landsat-8 OLI images, the terrain-corrected accuracy was 15 m and 12 m, respectively, in terms of 90% circular error (CE90, which means 90% of points have less than 15 m and 12 m positional error) [19; 20]. On 31 May 2003, the Scan Line Corrector (SLC), which compensates for the forward motion of Landsat 7, failed. As a result, the imaged area became duplicated, with a width that increased towards the scene edge. We used ArcGIS de-striping tools to mitigate this effect. For Landsat-8 images, layer stacking and mosaic tools were utilized to generate the 2017 Antarctic coastline map. To improve the consistency of the extracted coastline, we had to ensure that there was sufficient overlap between neighboring images. As for SAR images, precise orbit files that contain accurate satellite position and velocity information have been employed to geocode the imagery, and the geometric accuracy of SAR (i.e., ASAR and Sentinel-1 SAR) data was less than 1 pixel [21; 22]. Using SARscape software, backscatter calibration and range Doppler terrain corrections were applied. Backscatter calibration converted the Digital Number (DN) to a backscatter coefficient in decibels using calibration coefficients provided in image header files. Furthermore, the terrain correction shifted all the pixels to the correct geolocations according to the input DEM (digital elevation model) in the module of SARscape. The final extraction accuracy depends not only on the precision of improved Canny edge algorithm, but also on the geo-referencing accuracy of the Landsat and SAR images.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Satellite** & \begin{tabular}{c} **Spectral** \\ **Bands** \\ \end{tabular} & **Mode** & \begin{tabular}{c} **Polarization** \\ **Mode** \\ \end{tabular} & **Wavelength** & \begin{tabular}{c} **Pixel** \\ **Resolution (m)** \\ \end{tabular} & \begin{tabular}{c} **Number of** \\ **Images** \\ \end{tabular} \\ \hline Landsat-7 & \(1,2,3\) & - & - & - & \begin{tabular}{c} 1: 0.45–0.515 μm \\ 2: 0.525–0.605 μm \\ 3: 0.63–0.69 μm \\ \end{tabular} & 30 & \begin{tabular}{c} 131 in 2005 \\ 219 in 2010 \\ \end{tabular} \\ \hline Landsat-8 & \(2,3,4\) & - & - & \begin{tabular}{c} 1: 0.52–0.60 μm \\ 2: 0.63–0.69 μm \\ 3: 0.77–0.90 μm \\ \end{tabular} & 30 & \begin{tabular}{c} 131 in 2005 \\ 219 in 2010 \\ \end{tabular} \\ \hline ENVISAT & - & \begin{tabular}{c} Wide Swath \\ Mode (WSM) \\ \end{tabular} & HH, VV & \begin{tabular}{c} 5.331 cm \\ (C band) \\ \end{tabular} & 75 & \begin{tabular}{c} 134 in 2005 \\ 190 in 2010 \\ \end{tabular} \\ \hline Sentinel-1A & - & \begin{tabular}{c} Interferometric \\ Wide (IW) \\ \end{tabular} & \begin{tabular}{c} HH+HV, \\ VV+VH \\ HH, VV \\ \end{tabular} & \
\begin{tabular}{c} 5.405 cm \\ (C band) \\ \end{tabular} &
\begin{tabular}{c} 5.405 cm \\ 5 \(\times\) 20 \\ \end{tabular} & 5 in 2017 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of the Optical and synthetic aperture radar (SAR) images.