Global mapping of surface flow velocity and re-evaluation of the volume of the world's glaciers

The effects of climate change on water resources and sea level are largely determined by the size of the ice reservoirs around the world, which still remains largely uncertain. Ice flow defines the transfer of ice within a glacier and therefore largely governs the spatial distribution of the ice volume. Although some individual regions have been mapped, there is to date no global and complete view of glacier flow. In this study, we present a global mapping of surface ice flow velocity and use it to revise the ice thickness distribution and volume of glaciers around the world. Glacier surface flow velocities were calculated using Sentinel-2/ESA, Landsat-8/USGS, Venμs/CNES-ISA, Pléiades/AirbusD&S and radar data from Sentinel-1/ESA. We designed an automated workflow that (i) downloads the data from institutional or commercial servers, (ii) prepares the images, (iii) launches the feature tracking algorithm, (iv) calibrate the glacier surface velocities, and (v) mosaics the results to obtain filtered and averaged velocity maps. For years 2017 and 2018, glacier surface flow velocities are quantified for every possible repeat cycles from the nominal cycle of the sensor (2-16 days) up to more than one year. This new database of glacier surface flow velocity is used to construct an updated global ice volume based on the well known Shallow Ice Approximation approach. We discuss the quality of our global glacier surface flow velocity product and of our new ice volume reconstruction with respect to existing state of the art estimates and quantify the impact of our results in terms of sea level rise and water resources.