MEaSUREs: Small-Scale Kinematics of Arctic Ocean Sea Ice

This data set of the Arctic Ocean sea ice cover is derived from radar imagery. The data products were produced by the RADARSAT Geophysical Processing System (RGPS), a project supported by the NASA MEaSUREs program. The 4 types of products are: ice motion, ice deformation, ice age and thickness, and radar backscatter. The primary data source for the analysis is the Synthetic Aperture Radar (SAR) on RADARSAT-1, a Canadian polar-orbiting satellite that provided data coverage from October 1996 through May 2008.

Each product contains monthly measurements of ice motion and derived parameters over the Arctic Ocean sea ice cover. The analysis involves laying a 10km by 10km grid over a set of RADARSAT orbits covering the sea ice cover during an initial 3-day period of a season. The grid points are then tracked over each ensuing 3-day time period throughout the season. The changes in the cells defined by the grid points are used to characterize the evolution of the ice within each cell. We produce these measurements for two seasons: 1) winter usually covers November through mid-May, and 2) summer covers mid-May into mid-August.

The 4 data products resulting from these measurements are:

1) Ice Motion ? a record of the time and location of each point within the initial grid as tracked on RADARSAT images at approximate 3-day intervals. Note that a very small fraction of the points may be lost during the season through advection out of the Arctic basin, loss of ice, or untrackability of the ice cover.

2) Deformation ? a record of the divergence, vorticity and shear occurring within each cell. As the verticies of each cell move within a time step, the kinematic properties can be calculated to characterize the response of the ice cover to stresses induced by wind and ocean currents.

3) Ice Age and Thickness ? a record of the area, age and thickness of new ice and ridged ice that result from cell area changes. A spatial and temporal distribution of these ice areas is kept for each cell. If the area of a cell increases within a time step, an area of new ice is created. The ice thickness within all the new ice areas created during the season is increased using air temperature information. When the cell area decreases, the thinnest ice areas are rafted or ridged, depending on their thickness. The thickness of areas of ridged ice are also grown in time.

4) Backscatter ? a record of the radiometric properties of the ice within each cell. A histogram of the radar brightness is kept within each cell at each time step, allowing the user to deduce multi-year ice fractions of the ice cover.