In CD Proceedings: IEEE Workshop on Articulated and Nonrigid Motion, 27 June 2004
Discontinuous Non-Rigid Motion Analysis of Sea Ice using C-Band Synthetic
Aperture Radar Satellite Imagery
Cathleen Geiger
Mani Thomas
Video/Image Modeling and Synthesis Lab
Snow and Ice Branch
USACRREL
University of Delaware
Newark, Delaware
72 Lyme Rd, Hanover, NH 03755
manivt@cis.udel.edu
cathleen.a.geiger@erdc.usace.army.mil
Chandra Kambhamettu
Video/Image Modeling and Synthesis Lab
University of Delaware
Newark, Delaware
chandra@cis.udel.edu
Abstract
and Wilchinsky and Feltham [42] have made progress in
developing theoretical "anisotropic" sea-ice rheologies, but
Sea-ice motion consists of complex non-rigid motions in-
adequate data products to rigorously test their theories do
volving continuous, piece-wise continuous and discrete par-
not exist. Within the literature definitions of discontinuous
ticle motion. Techniques for estimating non-rigid motion
behavior such as "linear kinematic features" (LKFs) [27],
of sea ice from pairs of satellite images (generally spaced
[35], "piece-wise rigid motion" [35] and "aggregate scale"
three days apart) are still in the developmental stages. For
[23], [37] are beginning to emerge. The fundamental prob-
interior Arctic and Antarctic pack ice, the continuum as-
lem in defining these features is that their composition tran-
sumption begins to fail below the 5 km scale with evidence
scends any one scale, with several scales embedded upon
of discontinuities already revealed in models and remote
one another.
sensing products in the form of abrupt changes in magni-
Fundamentally, aggregate-scale sea ice is a piece-wise
tude and direction of the differential velocity. Using a hi-
continuous material made up of a collection of aggregated
erarchical multi-scale phase-correlation method and prof-
plates subject to the basic principles of continuum mechan-
iting from known limitations of cross correlation methods,
ics with limitations of those basic principles in close prox-
we incorporate the identification of discontinuities into our
imity to discontinuities. This definition places the motion
motion estimation algorithm, thereby descending below the
of sea ice under the larger category of non-rigid motion
continuum threshold to examine the phenomenon of discon-
analysis [26]. The interdisciplinary field of non-rigid mo-
tinuous non-rigid sea-ice motion.
tion involves the understanding of three basic types of ma-
terials, namely, continuous, piece-wise continuous, and dis-
crete particle motion. Depending on the scale, each of these
1. Introduction
descriptions applies to sea ice. At the large (basin) scale,
sea ice is traditionally regarded as a non-rigid continuum
Sea-ice consists of a collection of floes 1 with differential
and at the small scale it is regarded as a collection of dis-
crete particles/floes.
motion subject to non-local forcing at an aggregate-scale
with ranges from 10-300 km spatially and 1-20 days tem-
While progress has been made in understanding these
porally [37], [34]. This differential motion results in fea-
two outer scales of sea ice, the intermediate scale of piece-
tures such as leads, families of slip lines, cracks, and ridges.
wise continuous sea-ice motion is particularly difficult be-
Within the sea-ice community there is no formal definition
cause it goes beyond the limits of its scale with very narrow
of this scale. Coon, et al. [14], Aksenov and Hibler [1],
(i.e., small scale) crack-like features stretching thousands
of kilometers (i.e., basin scale). This scale is one which re-
1A single piece, large or small, of ice formed on the surface of an ocean
searchers have only recently been able to explore thanks to
or sea.
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