Gftt: an open-source tool for evaluating remotely sensed glacier
velocity products
Abstract
Glacier velocity reflects the dynamics of ice flow, and its change over
time serves a key role in predicting the future sea-level rise. Glacier
feature tracking (also known as offset tracking or pixel tracking) is
one of the most widely-used approaches for mapping glacier velocity
using remote sensing data. However, running this workflow relies on
multiple empirical parameter choices such as correlation kernel
selection, image filter, and template size. As each target glacier area
has different data availability, surface feature density, and ice flow
width, there is no one-size-fits-all parameter set for glacier feature
tracking. Finding an ideal parameter set for a given glacier requires
quantitative and objective metrics to determine the quality of resulting
velocity maps. The objective of our Glacier feature tracking test (gftt)
project is both to devise a set of widely applicable metrics and to
build a Python-based tool for calculating them. These metrics can be
thus used for comparing the performance of different tracking
parameters. We use Kaskawulsh glacier, Canada, as a test case to compare
the velocity mapping results using Landsat 8 and Sentinel-2 images,
various software packages (including Auto-RIFT, CARST, GIV, and vmap),
and a range of input parameters. To begin with, we calculate random
error over stable terrain, a metric that has been used for evaluating
the uncertainty of the velocity products. We develop two other workflows
for exploring new metrics and validating existing metrics, including the
test with synthetic pixel offsets and the comparison with GNSS records.
These existing and new metrics, calculated through the gftt software,
will help determine optimal parameter sets for feature tracking of
Kaskawulsh glacier and any other glacier around the world. This work is
supported by the NSF Earth Cube Program under awards 1928406, 1928374.