## 2 Materials and Methods
### Satellite Imagery  
#### 2.3.1 Radarsat-2  
For this project there are four major advantages of using RADARSAT-2 data, making it the most critical dataset for the study:  
1. Cloud-free images: Due to the large percentage of cloud cover in some areas of the Arctic, SAR imagery represents the only reliable source of data at a specific date and time.  
2. Orbit accuracy: RADARSAT-2 offers a 5 m orbit accuracy with a 90% level of confidence [24].  
3. Polarization: The fully polarimetric capability of RADARSAT-2 [25] will assist in coastline detection and image classification.  
4. Resolution and swath size: Fine mode with a resolution of less than 10 m and a swath of 50 km, and the dual polarization option make this mode very interesting for mapping at a scale of 1:50,000. Higher resolution images such as ultra-fine and spotlight modes could also be used, but the lack of a dual polarization option could be a limiting factor for images acquired during windy conditions with these modes [25].  
SAR data have become an important source of information for monitoring changes on land and water surfaces. The RADARSAT-2 sensor has been used operationally for monitoring and mapping changes in water bodies and wetlands [26; 27; 28]. The degree of backscatter change, resulting from surface roughness, depends on the intensity of wind and the incidence angle. In calm wind conditions, the water surface shows steady patterns represented by low and consistent backscatter, which is related to the surface water's regular nature. The effect of incidence angle has to be accounted for, particularly when using multi-temporal images acquired with different beam modes. Usually, a rough water surface will appear brighter when the incidence angle is small [29; 30]. The backscatter polarization also affects the separability between land and water. Earlier studies have shown that the HH polarization has lower backscatter over rough surface water, compared to the more sensitive VV polarization [27; 31]. The use of cross polarization HV and VH is hindered by a low backscatter coefficient over the targeted water surface as it is close to the sensor's noise floor.  
Figure 3: Mean, maximum and minimum daily water levels for the Mackenzie River at guage 10 MC008. The values represent monthly averages calculated using observations from 1982–2016 [21]. The low water period is between late October to early December with a river freeze up in mid-November; therefore, the best period to obtain ice free imagery would be late October to mid-November.  
In order to evaluate the best polarization to use in different wind conditions, two quad-polarization RADARSAT-2 images, representing the Fine Quad (FQ) 15 and FQ25 beam modes, were acquired on 7 October 2014 and 7 September 2016 respectively (Table 1). FQ15 and FQ25 are 25-km swath size images with a 9 \(\times\) 9 m resolution, collected at 35\({}^{\circ}\) and 44\({}^{\circ}\) incidence angles respectively. The FQ15 was acquired in windy conditions with wind blowing from east to west with a speed varying from 12 to 16 m/s. The FQ25 was acquired in calm to moderate wind conditions with a wind speed varying from 5 to 7 m/s and wind direction of south-east to north-west [32]. To chart the shoreline, a spotlight mode image was also acquired on 19 October, 2015 with the HH polarization. To conduct a segmentation and classification analysis, a fine mode image was acquired on 9 October, 2017 with HH and HV polarizations.