Abstract
Antarctic ice velocity maps describe the ice flow dynamics of the ice sheet and are one of the primary components used to estimate the Antarctic mass balance and contribution to global sea level changes. In comparison to velocity maps covering monthly to weekly time spans derived from the images of optical imaging satellites taken in recent decades, historical maps, from before the 1990s, generally cover longer time spans, e.g., over 10 years, due to the scarce spatial and temporal coverage of earlier satellite image data. We found velocity overestimations in such long-term maps that can reach from ~69 m a−1 (7-year span) in Totten Glacier, East Antarctica, up to ~930 m a−1 (10-year span) in Pine Island, West Antarctica. We propose an innovative Lagrangian velocity-based method for overestimation correction without the use of field observations or additional image data. The method is validated by using a set of “ground truth” velocity maps for Totten Glacier which are produced from high-quality Landsat 8 images from 2013 to 2020. Subsequently, the validated method is applied to a historical velocity map of the David Glacier region from images from 1972–1989 acquired during Landsat 1, 4 and 5 satellite missions. It is demonstrated that velocity overestimations of up to 39 m a−1 for David Glacier and 69 m a−1 for Totten Glacier can be effectively corrected. Furthermore, temporal acceleration information, e.g., on calving events, is preserved in the corrected velocity maps and can be used for long-term ice flow dynamics analysis. We recommend that overestimations of more than the velocity mapping uncertainty (1σ) be corrected. This velocity overestimation correction method can be applied to the production of regional and ice sheet-wide historical velocity maps from long-term satellite images.
Highlights
Ice flow velocity fields on the Antarctic ice sheet (AIS) have been mapped by using SAR and optical satellite images to study ice sheet-wide ice flow dynamics and AIS responses to global climate changes (Rignot et al, 2011a; Gardner et al, 2018; Shen et al, 2018; Greene et al, 2020a)
Velocity overestimation exists in Antarctic ice flow velocity maps produced from optical satellite images of long time spans
Such overestimations are inevitable for historical velocity maps due to the poor availability of earlier satellite images in Antarctica, especially before 1990
Summary
Ice flow velocity fields on the Antarctic ice sheet (AIS) have been mapped by using SAR and optical satellite images to study ice sheet-wide ice flow dynamics and AIS responses to global climate changes (Rignot et al, 2011a; Gardner et al, 2018; Shen et al, 2018; Greene et al, 2020a). It has not been brought to further attention in publications, given its nature and magnitude, this velocity overestimation issue should be fully understood and a comprehensive correction method should be developed so that corrected historical velocity maps can be analyzed alongside modern maps to create a long record of cohesive ice flow dynamics This 60 capability of building a long record of AIS ice flow dynamics is important for estimation of long-term AIS mass balance and prediction of the future GSL contribution (Rignot et al, 2019). The velocity change information is preserved after the correction and can be used for long-term ice flow dynamics analysis
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