Arctic Multiyear Ice Concentration Retrieval from SSM/I Data Using the NASA Team Algorithm with Dynamic Tie Points - Towards an Interdisciplinary Approach in Earth System Science - page 95

Fig. 2 Dynamic tie points from 1998 to 2007 (October May). Vertical bars show beginnings of

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November, January and May of each winter

Table 2 Average daily
change of dynamic tie points
from 1998 to 2007
(November

Surface
type

19 GHz H
(K)

19 GHz V
(K)

37 GHz V
(K)

T B ; aag T B ; aag T B ; aag

April)

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OW 0.51 0.26 0.22

MYI 0.41 0.26 0.37

FYI 0.24 0.20 0.24

The average absolute daily change T B ; aag of the dynamic tie points from 1998 to
2007 (November

April) are shown in Table 2 . The small daily change of tie points
in all channels and surface types con

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rms the tie points deriving procedure.

3 Time Series Results

Using fixed and dynamic tie points, both total and multiyear ice concentrations are

retrieved daily with the NASA Team algorithm for all winters (November April)

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from 1989 to 2012. Figure 3 shows the multiyear ice extent, de ned as the sum of

the area covered by grid cells that have 30 % or higher multiyear ice concentration
(Comiso 2012 ). Both multiyear ice retrievals show lower multiyear ice extent than
the annual minimum of the total ice extent in September. There are two reasons for
the differences. Firstly, the multiyear ice extent is extracted by ignoring pixels with
multiyear ice concentration below 30 %. Secondly, first year ice is already formed

at the time of the annual ice extent minimum in September.