## 3 Methods and Results
### Electro-Optical and Infrared
#### 3.1.4 Landsat 8  
Pansharpened Image  
Landsat 8 measures different ranges of frequencies (bands) along the electromagnetic spectrum. Among 11 bands, we used the panchromatic band (0.500-0.680 \(\upmu\)m) with 15 m resolution to pansharpen the 30 m resolution RGB color composite image. Figure 8 shows the forming process of hummocks near Axel Heiberg Island. A fragment of one stereo SPOT 6 image and DEM over the same area is shown in Figure 3.  
EIFs have certain properties that allow each feature to be detected and identified in optical imagery. First of all, MYHF and ice islands are much thicker than the surrounding sea ice. When a feature protrudes from the ice surface it creates brightness (intensity) variation in the image because of shadow and its bright pattern generated from the feature side oriented toward the sun. Another reason for brightness variation is that very often the EIF surface may have different roughness from other sea ice. The intensity variation in optical satellite imagery appears as texture, which is very often a specific property for certain EIFs. However, multiyear floes and rubble fields may have similar textures resulting in an ambiguity in feature identification when only the visible bands of optical images are used. A stereo DEM was used as an additional source of ground-truth information, which is a good indicator of EIF thickness. Figure 7: WorldView-2 images of ice features used to estimate height from shadow. Images © DigitalGlobe, 2014. (**a**)—ice island, (**c**)—forming hummock, (**b**,**d**)—ice island fragments. Landsat 8 has two thermal infrared (TIR) bands of 100 m resolution: Band 10 with the range of 10.6 to 11.2 \(\upmu\)m and Band 11 with the range of 11.5 to 12.5 \(\upmu\)m.  
For detecting EIFs in Landsat 8 imagery, a new method can be introduced that utilizes the TIR band for improving the identification of thicker ice features. The improvement is possible because thicker features have colder temperatures than the surrounding sea ice and appear dark and have the contrast from other ice features in the thermal image. The Landsat 8 thermal band has the following main limitations for identifying EIFs:  
* A coarse resolution (100 m);
* Sensitivity to the presence of even small amounts of cloud;
* Missing thermal contrast variation for the ice area at the edge of sea ice and open water;
* Thermal contrast may be caused by other features; in some cases thermal contrast was observed from multiyear floes and land-fast ice features;
* In the summer months, when snow is wet or ice is covered by melt pounds, the thermal band may not generate sufficient contrast for automated detection of thicker features. The following Figure 9 shows the typical appearance of EIFs in VHR imagery, a stereo DEM, and visible and thermal bands of Landsat 8. In optical-imagery ice islands have brighter and darker sides (Figure 9a,c) because of variation of the local sun-incidence angle. Ice-island thickness, as shown in Figure 9b, is a major factor that facilitates its identification. The same ice island can be identified in Landsat 8 using the visible (Figure 9c) and thermal (Figure 9d) bands. Ice-island fragments are similar to ice islands, but they are much smaller. The thermal signature in Landsat 8 can be visible only when there is a cluster of fragments shown as dark areas because the resolution (100 m) of the thermal band in many cases is coarser than the size of an individual fragment. Absence of thermal contrast may lead to missing individual fragments with automated detection. MYHFs can be identified based on textural information in combination with thermal contrast (Figure 10). As shown in Figure 10b, MYHFs are thicker than ice floes. Figure 10a-d show two MYHFs, with the larger one in the middle and the smaller one (the same as shown in Figure 4) in the top right corner. Greater thicknesses of MYHFs generate temperature difference between the MYHF and adjacent ice resulting in thermal contrast, as is shown in Figure 10d.