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Empirical correction of systematic orthorectification error in Sentinel-2 velocity fields for Greenlandic outlet glaciers
By utilising imagery from overlapping orbits, the Sentinel-2 programme offers high-frequency observations of high-latitude environments well in excess of its 5 d repeat rate, which is valuable for obtaining large-scale records of rapid environmental change. However, the production of glacier velocit...
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Published in: | The cryosphere 2022-07, Vol.16 (6), p.2629-2642 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | By utilising imagery from overlapping orbits, the
Sentinel-2 programme offers high-frequency observations of high-latitude
environments well in excess of its 5 d repeat rate, which is valuable for
obtaining large-scale records of rapid environmental change. However, the
production of glacier velocity datasets from optical feature tracking of
Sentinel-2 imagery is limited by the orthorectification error in ESA
products, which introduces significant systematic errors (on the order of
tens of metres) into displacement fields produced from cross-track image
pairs. As a result, most standard processing chains ignore cross-track
pairs, which limits the opportunity to fully benefit from Sentinel-2's
high-frequency observations during periods of intermittent coverage or for
rapid dynamic events. Here, we use temporally complete glacier velocity
datasets to empirically reconstruct systematic error, allowing for the
corrected velocity datasets to be produced for four key fast-flowing
marine-terminating outlets across the Greenland Ice Sheet between 2017–2021. We show that corrected data agree well with comparison velocity
datasets derived from optical (Landsat 8) and synthetic aperture radar
(Sentinel-1) data. The density of available velocity pairs produces a
noisier dataset than for these comparative records, but a best-fit velocity
reconstructed by time-series modelling can identify periods of rapid change
(e.g. summer slowdowns), even where gaps exist in other datasets. We use
the empirical error maps to identify that the commercial DEM used to
orthorectify Sentinel-2 scenes over Greenland between 2017–2021 likely
shares data sources with freely available public DEMs, opening avenues for
the analytical correction of Sentinel-2 glacier velocity fields in the
future. |
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ISSN: | 1994-0424 1994-0416 1994-0424 1994-0416 |
DOI: | 10.5194/tc-16-2629-2022 |