Evolution of the passive and active microwave signatures of a large sea ice feature during its 2 1/2-year drift through the Arctic Ocean

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Gohin, Francis, Cavanie, Alain, Ezraty, Robert
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Geophysical Union 1998
• Subjects: Arctic; Arctic Ocean; New Siberian Islands; Ostrova; Fram Strait; International Arctic Buoy Program; Sea ice
• Online Access: https://archimer.ifremer.fr/doc/00447/55848/58406.pdf; https://doi.org/10.1029/97JC03333; https://archimer.ifremer.fr/doc/00447/55848/

Although estimation of the total ice concentration from special sensor microwave imagers (SSM/I) has proven to be successful, none of the various algorithms developed to discriminate new and older ice provide satisfying results. While the strong contrast between the emissivity of sea ice and that of open water can be utilized to provide reliable estimators of the total ice concentration, passive microwave characteristics of second-year and multiyear ice may locally evolve in different ways, even during the cold season. Scatterometers, as the active microwave instrument in wind mode (AMI-wind) on board the European Remote Sensing Satellites (ERS), provide backscatter data which have a higher sensitivity to the surface topography of ice and a better stability in time, at a resolution compatible with the SSM/I measurements. Here we present the evolutions of the microwave properties of an ice feature appearing along the shores of Novosibirskiye Ostrova (New Siberian Islands) at the end of July 1992 as the ice ages during its 3-year drift toward the Fram Strait. The track of this well-defined ice surface is easily followed on the maps of the backscatter coefficient provided by the AMI-wind during the cold season. In summer, because of melting, the ice undergoes critical changes which alter its microwave signatures and hamper automatic tracking. Moreover, on approaching the Fram Strait the resolution of the scatterometer is not sufficient to capture the complex and rapid transformations of the ice cover. To compensate for this, buoy data obtained from the International Arctic Buoy Program are used, alone during summers or together with satellite data, to build basin-wide ice displacement fields. These displacement fields, successively applied to each pixel of the ice feature selected, provide a series of Lagrangian observations. During the drift, which ends in May 1995, the active and passive signatures evolve coherently, except for the cold season 1992-1993 when unrealistic multiyear ice concentrations are deduced from the brightness temperatures, which, at that time, are much less stable than the backscatter coefficient over the ice surface tracked, identified as second-year ice.