Sea ice tracking from SAR in the Arctic
PublisherUniversity of Sheffield
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Satellite observations play an important role in ice identification services because they are cost effective and efficient compared to extensive field campaigns. Radar data are extensively used to derive information about sea ice extent and move- ment. In the first part of this thesis I adapt a semi-automated algorithm, originally developed by Silva (2006) to track large icebergs in Antarctic waters, to track the movement of ice in the Northern Hemisphere. In addition to the move from Antarctic to Arctic waters, the algorithm is adapted to track sea ice rather than icebergs, with an attendant change in the shape of the tracked objects and their radar backscatter characteristics. The algorithm development is focused on the identification of appropriate image segmentation, brightness thresholding, and shape parameters appropriate to the identification and tracking of sea ice floes throughout the year. These developments are tested on images from a variety of locations, and from different SAR sensors. Recent literature documents the warming of the Arctic region (Alexandrov et al., 2004; Serreze et al., 2007) with an accompanying decline in sea ice cover (Kwok and Rothrock, 2009). The identification of ice extent and movement is an important tool in the study of climate variability (Spreen et al., 2006; Bochert, 1999); for example the magnitude of the sea ice flux through the Fram Strait is a measure of net ice production in the Arctic Ocean (Widell et al., 2003). The Fram Strait is of key importance for the export of ice from the Arctic (Kwok and Rothrock, 1999; Kwok et al., 2004) and well known for the presence of strong surface currents (Dickson et al., 2007; Fahrbach et al., 2001). In the second part of the thesis I investigate the competing influences of atmospheric and oceanographic forcings on ice export through the Fram Strait. The focus is on the western (Greenland) side of the strait between 79 - 81 ◦N. This area is within the East Greenland Current and also covers the boundary between fast ice and drift ice. The East Greenland Current, coupled with the prevailing northerly wind, is the main driver for ice export through the Fram Strait. On shorter temporal resolution ice movement is seen to be governed by the winds. Where the temporal resolution is greater than 1-2 days the influence of the East Greenland Current becomes more dominant and overall movement is towards the south. My results suggest that the prevailing wind speed and direction have a key impact on the rate of ice export through the Fram Strait. A period in which the wind forcing is in agreement with the East Greenland Current will see greater ice export than a period in which the two are acting in opposite directions.