## 6 Conclusions  
Keeping over 1000 nautical charts up to date is a challenge that CHS faces, primarily in dynamic areas such as the Mackenzie River. In this paper, CHS has proposed several techniques to improve the quality of charts using a multi-sensor SRS approach. The proposed hybrid approach, that leverages the advantages of SAR and optical data, is a cost effective and accurate technique to update charts in dynamic areas. The use of RADARSAT-2 is beneficial for capturing low water conditions during periods of high cloud cover (October to December), thus ensuring that shorelines representing the lowest water level possible is mapped. RADARSAT-2 orthoimages have a horizontal accuracy of 5 m which is important to ensure high positioning accuracy for safe navigation. It is suggested to use both HH and HV polarizations for classification in order to increase the contrast between land and  
Figure 14: Example of the current edition of Chart 6424 (left) and prototype chart updated with EO data and new survey data from CCG vessels (right) [3]. Figure 13: (a) Landsat-8 imagery from 5 August, 2015 and (b) RADARSAT-2 imagery from 6 October, 2015 are combined in (c) to display an example of how a combination of optical and radar imagery can identify islands and drying areas on charts. water, and to improve the retrieval accuracy. As RCM will be replacing the RADARSAT-2 mission, the compact polarimetry parameters RH and RR of RCM proved to behave similarly to HH/HV polarizations for separating land and water, and more specifically for the detection of mudflat areas. One weakness of SAR data is that image noise can make interpretation difficult, especially under windy acquisition conditions. Since it is difficult to acquire cloud-free optical imagery during the low water period, having an optical multispectral image acquired during the summer months helps with land/water interpretation and is also beneficial to differentiate between land and drying areas. Object-based image segmentation applied to RADARSAT-2 and optical imagery allowed for excellent separation of land and water features for a northern section of the Mackenzie River. A comparison of the extracted river channel and tributaries with CHS chart 6428 revealed significant differences in the river's location. In some instances, nearly the full width of the river currently passes through areas of land identified on the chart. After extracting the shoreline of six historical Landsat images of the area, the Mackenzie River shoreline was measured to be moving at a rate of approximately 20 m/year in areas of maximum change. This change indicates that the chart should be updated every 2-3 years in order to ensure safe navigation for mariners. To further improve the quality of charts, CHS proposed applying the following steps:  
1. applying segmentation and classification to acquired SAR and optical datasets to chart the full length of the Mackenzie river as well as other dynamic coastal areas in Canada;  
2. using multi-temporal data to understand river dynamics at various water levels throughout the year, and  
3. acquiring crowdsourced survey data from ships passing through the Mackenzie River, such as the CCG. Through additional work to extend the application of the studied approach across the entire length of the Mackenzie River system, we expect significant improvements to the charting of dynamic river systems across Canada. There are also many other areas of Canadian waters that are dynamic. For example, the Arctic coastline is retreating by half a meter per year [46]; the changes are particularly dramatic in the Beaufort Sea along the coast of the Northwest Territories and Yukon Territory. The constant erosion of coastlines and poor source data has led CHS to look at alternative solutions for mapping and surveying Canadian waters. Other hydrographic offices, such as the National Oceanic and Atmospheric Administration (NOAA), are exploring remote sensing techniques to better chart dynamic areas.