Long-term and seasonal scale changes in surface flow velocity and frontal position of Greenland's outlet glaciers using Landsat optical imagery

We present an innovative method that allows for a more precise mapping of glacier flow velocities in Greenland based onf Landsat standard products. An enhanced orthorectification scheme in combination with a destriping correction of the Landsat-7 SLC-off products was applied and leads to an improved accuracy of the derived flow vectors. In combination with a novel filter algorithm that significantly reduces spurious errors from the feature tracking results our automatic approach is particularly suitable for the determination of flow fields in high temporal resolution from large data sets. Moreover, we developed an automatic method to infer the terminus positions of outlet glaciers. The knowledge of glacier velocities and terminus position is a major requirement for mass flux and mass balance estimates. Most of the Greenland outlet glaciers were only observed with a low temporal resolution. However, a high temporal resolution especially during the melt season is neccessary to understand the processes acting in the dynamic areas of the Greenland Ice Sheet. In this study, we utilised Landsat ETM+, TM and MSS optical imagery to infer surface flow velocities and frontal positions of more than 300 outlet glaciers in Greenland. We utilised over 10,000 Landsat scenes between 1972 and 2012 to determine the flow regime along the coastal regions of Greenland south of 83°N. Depending on the scene coverage we determined between 200 and 2000 velocity fields of each outlet glacier with a spatial resolution of 300 m. The high temporal resolution of the velocities fields were used to infer seasonal and interannual changes in the flow regime. To study the long-term flow evolution we extended the time series back to 1972 by using Landsat MSS imagery. We mapped the retreat and advance of more than 150 glaciers. Additionally, calving rates of glaciers were determined by combining both the frontal position and the terminus velocity.