Evaluating Sea Ice Deformation in the Beaufort Sea Using a Kinematic Crack Algorithm with RGPS Data

Abstract

Sea ice in the Arctic plays an important role in the Earth’s climate and has been an early indicator of global warming. Remote sensing data, particularly synthetic aperture radar (SAR) imagery of Arctic regions, can help us understand the complex processes controlling sea ice dynamics and thermodynamics. The RADARSAT Geophysical Processor System (RGPS) was developed by the Polar Remote Sensing Group at the Jet Propulsion Laboratory (JPL) to extract sea ice motion data from SAR imagery. A set of points initially forming a regular grid is tracked providing displacements at each point over time. If the set of points in the original configuration is viewed as the vertices of square cells then the motion of the points determines the deformation of the cells. With this interpretation, grid quantities such as divergence, shear, and vorticity can be approximated using the nodal displacements. In this work an alternative approach for evaluating the deformation of sea ice from these data is proposed that uses the deformation gradient and a kinematic crack algorithm. With this approach, the deformation in a cell is assumed to be due solely to a displacement discontinuity caused by a crack. Then a minimization approach is used to find the crack dimension and orientation for each cell that best fits the nodal displacements. The kinematic crack algorithm is illustrated using RGPS data for a period of 16 days in February and March of 2004 for a region in the Beaufort Sea lying between Banks Island in the East and Point Barrow in the West.