A processing system to monitor Greenland outlet glacier velocity variations at decadal and seasonal time scales utilizing the Landsat imagery

In this paper we present a monitoring system for area-wide flow-velocity fields of the outlet glaciers of the Greenland Ice Sheet (GrIS) utilizing the freely available Landsat archive. In order to process this large amount of satellite images an almost automatic monitoring system was developed. With the Global Digital Elevation Map V2 (GDEM-V2) of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) an improved orthorectification was applied which, in combination with a destriping correction of the Landsat 7 products with Scan Line Corrector (SLC) failure, leads to more precise flow-velocity information. In addition, outliers were removed using an adaptive, recursive filter approach. For the time span 1972-2012 more than 100,000 flow-velocity fields were derived from over 16,000 optical multi-sensoral Landsat scenes (Landsat 1 to Landsat 7) allowing the determination of the long-term flow-velocity trend. Moreover, the high temporal resolution facilitates the analysis of seasonal flow-velocity variations of numerous outlet glaciers. For many of the major outlet glaciers the results show an acceleration pattern that is consistent with most of the previously published analyses. However, the flow-velocity changes do not have a uniform pattern in their temporal and spatial distribution. This study provides both a high temporal densification and an extension of existing flow-velocity information of the GrIS margin. Finally, this processing chain in its generality allows for the determination of various types of surface displacements and can be applied to other glacier regions.