Two-dimensional analysis of ice ridging in the Beaufort Sea using aerial photography

Abstract

Aerial photography was obtained for the Beaufort Sea north of Tuktoyaktuk. The flight path covered two distinct ice zones over a 15.5 km transect extending perpendicular to the coast, yielding fifty-nine photographs at a scale of 1 : 2000. The process of ridge extraction was automated using a series of computer algorithms for image filtering, edge detection and edge linking. Examples from two different sections along the transect are chosen for presentation: (a) a heavily ridged area, and (b) an area with one dominant linear ridge feature that separates ice cover of different age. Two parameters used in the automated process, a minimum edge gradient and minimum number of connected pixels said to form a continuous ridge segment, influence the number, length and spatial pattern of extracted ridges. Direct one-to-one correlations between manually interpreted ridges from photographs and the algorithm extracted ridges from digital data are not always possible. However, results indicate that the automated ridge extraction procedure reliably characterizes the overall direction and density of the ice ridges. The distribution of the ice-ridge directions is estimated from circular (angular) histograms constructed directly from the digital data. Analysis of the Beaufort Sea transect reveals that the ice ridging is strongly anisotropic, with a principal direction parallel to the local coastline.