Detecting wave patterns in Arctic nearshore waters using SAR imagery at Herschel Island - Qikiqtaruk, Yukon, Canada

Abstract

The Arctic is one of the most impacted regions by climate change. Rising air temperatures and the shortening of sea ice periods lead to accelerated erosion rates of permafrost coasts. With coastal erosion, the input of sediment and organic matter into nearshore waters increases, influencing local economies, ecosystems and climate by releasing greenhouse gases. When investigating erosion processes in the Arctic, mechanical erosion by ocean waves is an important factor that must be considered. However, spatial and temporal patterns of significant wave heights ($H_s$) in these waters are not well known, since in situ measurements are often costly and time consuming and optical spaceborne imagery is bound to cloud free and daylight conditions. The aim of this study is to use the empirical XWAVE algorithm on high resolution SAR X-band imagery to investigate patterns of wind generated $H_s$ in an Arctic nearshore environment that is threatened by rapid coastal erosion. Several TerraSAR-X and TanDEM-X scenes were combined to calculate means of $H_s$ under changing wind conditions in the coastal waters of Herschel Island Qikiqtaruk (HIQ) in the western Canadian Arctic since 2009. We use calibrated mulitlook data acquired in the Strip Map mode with dual and single polarisation and the XWAVE algorithm to calculate the sea state of each available ice free scene in that region. We map the spatial patterns of $H_s$ under different wind conditions and time periods in order to find significant wave patterns that might influence coastal morphology. First results show that over the ice free period, waves appear to be highest northwest of the island while there is a long calm strip along the southeast coastline. This matches the overall westerly wind regime through which HIQ protects the easterly nearshore waters. The northwestern sea state is also characterised by the highest variability in $H_s$ which could coincide with the fetch length depending on sea ice conditions further off-shore. In contrast, the eastern and south-eastern near-shore sea state is more stable as these waters are bordered by land. Our results show the potential of SAR imagery to detect sea state patterns in remote environments, but also show the need to specifically tune the algorithm to nearshore waters.