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slightly vary <strong>the</strong> IMS with this product when o<strong>the</strong>r external sources suggest <strong>the</strong> MMAB may be<br />

contaminated with a false emissivity.<br />

A B<br />

Figure 1. The 24km IMS product (A on <strong>the</strong> left) <strong>as</strong> remapped from <strong>the</strong> 4km IMS (B on <strong>the</strong> right) for May 19,<br />

2006. The 24km represents <strong>the</strong> same l<strong>an</strong>d/sea m<strong>as</strong>k used in previous 24km products prior to February 2004.<br />

Note <strong>the</strong> differences in representations for mountainous snow, inl<strong>an</strong>d lakes, <strong>an</strong>d sea ice leads.<br />

Daily NIC Ice Edge<br />

In its inception, <strong>the</strong> IMS w<strong>as</strong> designed to exploit <strong>the</strong> NIC weekly ice charts for <strong>the</strong> Nor<strong>the</strong>rn<br />

Hemisphere. The NIC produced detailed sea ice maps coded in <strong>an</strong> ice charting nomenclature<br />

known <strong>as</strong> egg code once per week, usually updating <strong>the</strong> product on Friday afternoons, until 2001.<br />

Since that time <strong>the</strong> NIC switched from weekly to biweekly hemispheric coverage. This decre<strong>as</strong>ed<br />

<strong>the</strong> utility of <strong>the</strong> charts for daily operational ice mapping. Fur<strong>the</strong>rmore, ice charts rele<strong>as</strong>ed on<br />

Fridays would use input data typically three to seven days old for <strong>the</strong> <strong>an</strong>alysis. While <strong>the</strong> NIC<br />

charts could still provide a general outlook of ice thickness <strong>an</strong>d ice distribution, <strong>the</strong> dynamic<br />

nature of ice made <strong>the</strong> charts too old for <strong>the</strong> IMS <strong>an</strong>alysis. Since February 2004, a daily vector sea<br />

ice edge h<strong>as</strong> been incorporated into <strong>the</strong> IMS. The NIC daily sea ice vector product applies visible,<br />

infrared, p<strong>as</strong>sive microwave, <strong>an</strong>d radar data to outline those are<strong>as</strong> with >10% ice cover. This<br />

product differs from <strong>the</strong> IMS product in three key ways. First, <strong>the</strong> NIC product is vector-b<strong>as</strong>ed <strong>an</strong>d<br />

attempts to enclose amorphous polygons, while <strong>the</strong> IMS defines ice cover within predefined<br />

pixels. The NIC ice cover h<strong>as</strong> no set size requirements on <strong>the</strong> polygon size or shape, thus <strong>the</strong> scale<br />

of what are<strong>as</strong> enclose >10% is at <strong>the</strong> NIC <strong>an</strong>alyst’s digression. This often leads to smoothing along<br />

<strong>the</strong> ice edge in some are<strong>as</strong>, while o<strong>the</strong>r are<strong>as</strong> may be more detailed th<strong>an</strong> <strong>the</strong> IMS. Experience h<strong>as</strong><br />

revealed more of <strong>the</strong> former th<strong>an</strong> <strong>the</strong> latter. A second difference in <strong>the</strong> products is <strong>the</strong> ice<br />

concentrations captured by each product. The NIC outlines are<strong>as</strong> with >10% ice cover, while <strong>the</strong><br />

IMS demarcates are<strong>as</strong> with >50% ice cover. IMS <strong>an</strong>alysts must adjust for this difference when<br />

using <strong>the</strong> NIC daily ice edge for IMS input. A third difference in <strong>the</strong> ice <strong>an</strong>alysis output is <strong>the</strong><br />

IMS’s inclusion of lake ice. The NIC vector ice edge only outlines sea ice <strong>an</strong>d lake ice in <strong>the</strong> Great<br />

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