Abstract
ABSTRACTThe presence of leads with open water or thin ice is an important feature of the Arctic sea ice cover. Leads regulate the heat, gas and moisture fluxes between the ocean and atmosphere and are areas of high ice growth rates during periods of freezing conditions. Here, an algorithm providing an automatic lead detection based on synthetic aperture radar images is described that can be applied to a wide range of Sentinel-1 scenes. By using both the HH and the HV channels instead of single co-polarised observations the algorithm is able to classify more leads correctly. The lead classification algorithm is based on polarimetric features and textural features derived from the grey-level co-occurrence matrix. The Random Forest classifier is used to investigate the importance of the individual features for lead detection. The precision–recall curve representing the quality of the classification is used to define threshold for a binary lead/sea ice classification. The algorithm is able to produce a lead classification with more that 90% precision with 60% of all leads classified. The precision can be increased by the cost of the amount of leads detected. Results are evaluated based on comparisons with Sentinel-2 optical satellite data.
Highlights
Sea ice covers a large part of the Arctic Ocean
The procedure for texture feature ranking described in the last section was carried out three times: one time for the band product data (HH·HV), the second one for the HH band data and the third one for the band ratio (HH/HV)
Blue lines stand for classification of the band product, green lines stand for classification of the HH band and red for the band ratio products
Summary
Sea ice covers a large part of the Arctic Ocean. Leads are areas with open water or thin ice, which are usually of elongated shape. They appear as result of ice fracturing due to shear and divergence stresses in the sea-ice cover. These stresses are forced by the ocean currents, tides and to a large degree by winds in the atmosphere. The mapping of sea-ice leads plays an important role for navigation providing an easier way for vessels through the pack ice. leads are areas of increased biological activity in the ocean like phytoplankton blooms (Assmy and others, 2017). The life of Arctic animals (e.g. walruses, polar bears, birds) is often tied to leads
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