Arctic Multiyear Ice Concentration Retrieval from SSM/I Data Using the NASA Team Algorithm with Dynamic Tie Points

Abstract

We retrieve multiyear ice concentration with the NASA Team algorithm and a modified NASA Team algorithm with dynamic tie points. The latter is used to compensate the temporal impact of brightness temperature variations. To assess the performance of both methods, analyses were made for all winters from 1989 to 2012. The method with dynamic tie points yields higher estimates in most years. Both methods show a clear declining trend of the multiyear ice area from 1989 to 2012, which is consistent with the decrease of the annual minimum ice extent. Furthermore, the ice extent of multiyear ice in most years decreases during each winter, reflecting the expected loss of multiyear ice by export to lower latitudes. A sensitivity study to evaluate the influence of each tie point on multiyear ice concentration retrieval shows that the retrieval is most sensitive to the tie points of multiyear ice and first year ice at 19 GHz vertical polarization. Therefore, these tie points need to be determined more precisely if dynamic tie points are used for multiyear ice retrieval with the NASA Team algorithm.