Preprints
https://doi.org/10.5194/tc-2022-33
https://doi.org/10.5194/tc-2022-33
 
03 Mar 2022
03 Mar 2022
Status: a revised version of this preprint is currently under review for the journal TC.

Empirical correction of systematic orthorectification error in Sentinel-2 velocity fields for Greenlandic outlet glaciers

Thomas R. Chudley1, Ian M. Howat1,2, Bidhyananda Yadav1, and Myoung-Jong Noh1 Thomas R. Chudley et al.
  • 1Byrd Polar and Climate Research Center, Columbus, OH, USA
  • 2School of Earth Sciences, Ohio State University, Columbus, OH, USA

Abstract. By utilising imagery from overlapping orbits, the Sentinel-2 programme offers high-frequency observations of high-latitude environments well in excess of its 5-day 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. 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 agrees 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.

Thomas R. Chudley et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-33', Jeremie Mouginot, 07 Apr 2022
    • AC1: 'Reply to RCs', Tom Chudley, 03 May 2022
  • RC2: 'Comment on tc-2022-33', Bas Altena, 28 Apr 2022
    • AC2: 'Reply to RCs', Tom Chudley, 03 May 2022

Thomas R. Chudley et al.

Thomas R. Chudley et al.

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Short summary
Sentinel-2 images are subject to distortion due to orthorectification error, which makes it difficult to extract reliable glacier velocity fields from images from different orbits. Here, we use a complete record of velocity fields at four Greenlandic outlet glaciers to empirically estimate the systematic error, allowing us to correct glacier velocity fields to a comparable accuracy to other medium-resolution satellite datasets.