A pattern-based strategy for InSAR phase unwrapping and application to
two 2 landslides in Colorado
Abstract
Interferometric synthetic aperture radar (InSAR) has been successfully
used to map ground displacements associate with landslides. One
challenge with InSAR is that the basic measurement of interferometric
phase takes values between 0 and 2π instead of values representing total
displacement relative to some stable reference frame. Phase unwrapping
is necessary to reconstruct measurements of total displacement for use
in quantitative analysis. Unwrapping approaches often assume that the
absolute phase difference between two neighboring pixels should be a
small fraction of a cycle (π or less). In the presence of noise or high
strain rates associated with fast-moving landslides, aliasing of the
phase (under-sampling of the wrapped signal) can result in unwrapping
errors and under- or overestimates of total displacement. Here we use a
pattern-based strategy for phase unwrapping of InSAR observations of
fast-moving landslides, where we determine the unwrapped deformation
field that is most similar to a scaled reference displacement map. We
also describe a range of metrics that we use to evaluate the most
appropriate scaling for each interferogram and demonstrate the range of
conditions where they perform well using synthetic data. For evaluation
of the results, we generated UAVSAR wrapped interferograms over the
Slumgullion landslide in Colorado where phase aliasing for
interferograms with temporal baselines larger than seven days is common.
We show the interferograms unwrapped with our approach and compare them
against results from range offsets (pixel tracking), demonstrating that
our approach can be used for time spans well beyond those where
traditional phase unwrapping performs well.