A grid-based algorithm for the extraction of intermediate-scale sea-ice deformation descriptors from SAR ice motion products

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Abstract
The characteristics of, and preliminary results from, a grid based automatic computer algorithm for the extraction of quantitative measures of seaice deformation from Synthetic Aperture Radar (SAR) data sets, are described. The data sets utilized are the sequential fields of ice movement vectors that are produced by the Geophysical Processor System (Gp,S) of the Alaska SAR Facility (ASF). The algorithm utilizes the temporal changes in the size and the shape of each original 5 by 5km grid element to calculate the convergence, the divergence, and the shear of the ice. An attempt is made to minimize the effect of random positioning errors, which are intrinsic in the determination of motion fields by a feature matching system such as the GPS, by eliminating some isolated deformation cells and by the use of minimum deformation values that are set by the investigator. The overall deformation values of the remaining major deformation features are calculated by the integration of the deformation values of the individual grid elements within the features. The algorithm makes possible the rapid screening and extraction of significant ice deformation events without the necessity of looking at either the SAR images or at ice motion products on which no significant ice deformation occurred. As a demonstration, the temporal variations in ice deformation are obtained, for a 6 month period during the winter of 1991–1992, for a circular sampling area with a radius of 200km centred at 81°N and 170°W in the Chukchi Sea portion of the Arctic Ocean. 1. Introduction

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