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Advice on using the MMAB Ice concentrations

The passive microwave ice concentrations produced by the MMAB are not replacements for operational analysis products such as those produced by the Alaska Region office of the NWS. The Alaska Region does use the MMAB ice fields in constructing their products, so it is possible that other users may find the MMAB products useful as well.

Advice on Interpreting the MMAB Ice concentrations

The MMAB ice fields are produced from a passive microwave sensor (AMSR-E as of May 2009; SSMI from F-15 and SSMI-S from F-17 since June 2012). This gives a relatively limited resolution output - 12.7 km, 6.9 nm, as of 27 August 2004 (previously 25.4 km from SSMI, 12.7 km SSMI from then to the May 2009 usage of AMSR-E). The image displayed on the web page is not interpolated, so that you can see where the image cells are.

The image itself displays the ice concentration in intervals. Special colors are pale purple ('weather'), darker purple (no data), gray (too much land near the cell for reliable ice concentrations), and black (land). Red indicates low concentrations (16 to 28 percent), while blues indicate high ice concentrations (over 85%). The color bar on the web page gives the full description of the relation.

The NASA Team 2 algorithm is now used to estimate the ice concentrations. The analysis system as implemented by MMAB in 1996 is described in a technical note which is available in print as well as on-line. A newer note is in preparation regarding the details of the current system. The algorithm works by comparing the observations to signatures typical of different ice types.

Things other than ice can give an ice signature. This includes high seas and high precipitation rates. There is a filter which removes most of this contamination from the ice field, but it is not always effective. Most of the time, the false ice reports are for low concentration. This occurred on 8 January 1997, for example, at a time when Russ Page, in the Anchorage WSFO, told me there were 60 knot winds in the Bering Sea.

Conversely, in the summer, the layers and puddles of water which can accumulate on the surface of the ice floes mislead the algorithm in to underestimating the total ice concentration.

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Page last modified: Tuesday, 28-Aug-2018 13:40:09 UTC