| Summary: | A feature of the sea-ice cover over coastal areas is the appearance of coastal polynyas, which form by offshore wind and/or ocean current. In Antarctic coastal polynyas, high production of sea ice occurs due to huge heat loss to atmosphere, resulting in the formation of dense water, precursor of Antarctic Bottom Water. Therefore, Antarctic coastal polynyas have important roles in ocean thermohaline circulation. Sea-ice production within polynyas is directly related to polynya ex- tent and thin-ice thickness within the polynya. Thus, it is important to detect thin ice thickness accurately and examine the factor determining polynya extent and the variability. Several studies have developed algorithms for estimation of the thin ice thickness from brightness temperature (TB) of satellite passive microwave sensor. In these algorithms, ice thickness of less than 20 cm is empirically esti- mated by utilizing negative correlation between the ice thickness and a ratio of the horizontally to vertically polarized TBs (PR). Several studies also have extended these algorithms to mapping of sea-ice production for Antarctic coastal polynyas, and the factor determining polynya extent has been investigated using sea-ice data obtained from these algorithms. However, ice type, which has an in uence on mi- crowave characteristic of thin-ice, has not been considered in these algorithms. Thin ice (polynya) areas are classi ed roughly into two types. One is active frazil type: a mixture of open water and frazil/grease ice areas. The other is thin solid ice type: nearly uniform thin ice covered area. It has been speculated that the difference in these ice types causes reduced accuracy of the ice thickness algorithm. In addition, the information of ice type is necessary to examine polynya mecha- nism because each ice type likely has different formation and variability process. In this study, we developed high accurate thin ice algorithm with discrimination of ice type, and examined the formation and variability of Antarctic coastal ...
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